INTRODUCE 797B OFF-HIGHWAY TRUCK

797B Off-highway Truck

INTRODUCTION

Shown is the left side of a 797B Off-highway Truck.  The 797B is the largest Caterpillar truck.

* Rear brake oil coolers (1)
* Fuel tank (2)

Shown is the right side of a 797B truck.

* The large hydraulic tank (1) shown in the center of the truck is actually three separate hydraulic           tanks
* Located in front of the hydraulic tanks are the steering and fan drive oil cooler and the two front         brake oil coolers (2).

Shown is the front of a 797B truck.

The 797B trucks use a folded-core style radiator. The folded-core style radiator provides the convenience of repairing or replacing smaller individual cores.

Shown is the rear of a 797B truck.

The truck bodies on 797B trucks are mandatory options.  Several body styles are available.  The weight of the available body styles range from 38000 kg (84,000 lbs) to 63000 kg (140,000 lbs), which will affect the load carrying capacity of the truck.

797B changes include:

General Machine:
* Serial number prefix changed from 5YW to JSM
* Increased load carrying capacity from 327 Metric tons (360 tons) to 345 Metric tons (380 tons)
* Increased Gross Machine Weight (GMW) from 559090 kg (1,230,000 lbs.) to 623690 kg                      (1,375,000 lbs)
* Empty weight (no body)--214820 kg (473,600 lbs.)
* Body weight--38000 kg (84,000 lbs) to 63000 kg (140,000 lbs)
* Increased tire size from 58/80R63 to 59/80R63
* Length--14.53 meters (47.8 ft)
* Width--9.76 meters (32 ft)
* Height--7.58 meters (24.9 ft)
* Body Up Height--15.29 meters (50.2 ft)
* Maximum ground speed at 1900 engine rpm--67.6 km/h (42 mph)

MAINTENANCE

Before working on or operating the truck, read the Operation and Maintenance Manual thoroughly for information on safety, maintenance, and operating techniques.

Safety Precautions and Warnings are provided in the manual and on the truck.  Be sure to identify and understand all symbols before starting the truck.

The first step to perform when approaching the truck is to make a thorough walk around inspection.  Look around and under the truck for loose or missing bolts, trash build-up, and for coolant, fuel, or oil leaks. Look for indications of cracks. Pay close attention to high stress areas as shown in the Operation and Maintenance Manual.

797B maintenance points

Shown are all of the 797B maintenance points.  Some of the items shown, such as all fluid levels, should be checked daily (see next visual).  Some of the items shown, such as engine air filters, should be checked when required.  Maintenance intervals for these items depend mostly on the local conditions.  Some locations have more dust and some locations have loaded uphill hauls while others have loaded downhill hauls.  All of these factors must be considered for some of the maintenance operations.

Most of the maintenance operations are performed at a specific time or engine hour interval.  The maintenance interval for each operation can be found in the Operation and Maintenance Manual.

Fuel consumption is the most accurate method for determining maintenance and overhaul intervals.  When a machine is sitting stationary with the engine running, the hour meter is also running, but there is little wear and tear on the machine unless there is overcooling or overheating of the engine. Fuel consumption is almost zero during idling conditions. Fuel consumption increases significantly during load conditions and therefore is a good indication of actual machine usage.

Maintenance 10 hours/daily

The following list identifies the items that must be serviced every 10 Hours or Daily.
* Walk-Around Inspection: Check for loose bolts, leaks, and cracks
* Suspension cylinders:  Measure/recharge
* Hoist and brake system oil:  Check level
* Steering system and fan drive oil:  Check level
* Rear axle oil:  Check level
* Fuel tank:  Drain moisture/Check level
* Transmission/Torque Converter oil:  Check level
* Engine Crankcase and Coupling oil:  Check level
* Air tanks:  Drain moisture
* Auto lube (grease) tank:  Check level
* Radiator:  Check level and radiator core plugging
* Air filters and precleaners: Check restriction with VIMS
* Indicators and gauges:  Test operation
* Seat belt:  Inspect
* Back-up alarm:  Test operation
* Brakes:  Check operation
* Secondary steering:  Test operation.

Front wheel bearing magnetic inspection plug

The front wheel bearing oil level is checked and filled by removing the plug (1) in the center of the wheel bearing cover. The oil should be level with the bottom of the plug hole.  The oil is drained by removing the drain plug (2).  The drain plug and the fill plug are both magnetic plugs.
Inspect the plugs periodically for metal particles.  If any metal particles are found, remove the wheel cover and inspect the bearings for wear.
The service interval for changing the front wheel bearing oil is 500 hours. Use only Final Drive and Axle Oil (FDAO) with a specification of (FD-1)
or Transmission Drive Train Oil (TDTO) with a specification of (TO-4) or
newer.  FDAO and TDTO TO-4 provides increased lubrication capability for bearings.
Check the tire inflation pressure. Operating the truck with the wrong tire inflation pressure can cause heat build-up in the tire and accelerate tire wear.


NOTE:  Care must be taken to ensure that fluids are contained while performing any inspection, maintenance, testing, adjusting, and repair of the machine.  Be prepared to collect the fluid in suitable containers before opening any compartment or disassembling any component containing fluids.  Refer to the "Tools and Shop Products Guide" (Form NENG2500) for tools and supplies suitable to collect and contain fluids in Caterpillar machines.  Dispose of fluids according to local regulations and mandates.

Front suspension cylinder charge inspection

Check the front suspension cylinders for leaks or structural damage. Check the charge condition of the front suspension cylinders when the truck is empty and on level ground.  Measure the charge height of the suspension cylinders and compare the dimension with the dimension that was recorded the last time the cylinders were charged.  Recharge the cylinders with oil and nitrogen if necessary.

If the front suspension cylinders must be recharged, they must first be drained of all nitrogen and oil.  Then, charge the cylinders with 13 mm
(0.5 in) of 10W HYDO type oil.  After the oil charge, raise the cylinders with nitrogen and install a 265 mm (10.4 in) gauge block between the spindles and the suspension cylinder housings. Lower the nitrogen pressure until the weight of the truck is resting on the gauge blocks. Set the nitrogen pressure to 2790 kPa (405 psi) and let the pressure equalize in the cylinders for five minutes.  When finished, raise the body and remove the gauge blocks.  The normal charge height when sitting empty on level ground is approximately 224 mm (8.80 in).
Two grease outlet fittings (1) are located on the front of each suspension cylinder.  The grease supply line for the Auto Lubrication System is located at the rear of the suspension cylinder.  No grease outlet fittings should be located on the same side of the suspension cylinder as the grease fill location. Having an outlet fitting on the same side of the suspension cylinder as the grease fill location will prevent proper lubrication of the cylinde
Make sure that grease is flowing from the outlet fittings to verify that the suspension cylinders are being lubricated and that the pressure in the cylinders is not excessive.

Three steering accumulators (2) are located behind the right front tire. The steering accumulators provide the supply oil during normal operation and temporary secondary steering if a loss of pump oil flow occurs.  The accumulator nitrogen charge pressure is 7230 kPa (1050 psi) at 21°C (70°F).  Check the nitrogen charge pressure every 500 hours.

To charge the steering accumulators, use the 175-5507 Nitrogen Charging Group and the 152-2023 Accumulator Charging Group.  Follow the procedure in the Special Instruction, "Repair Procedure for Bladder-Type Accumulators for Off-highway Truck/Tractors" (Form SEHS8757).

Steering oil from the solenoid and back-up relief valve manifold returns to the steering tank through the steering and fan drive oil return filters (3). The hydraulic fan drive oil also returns to the tank through these filters

Steering solenoid and relief valve manifold.

The steering solenoid and relief valve manifold (1) is located on the frame near the right side of the front engine module. Return oil from the fan drive motor joins with the steering system return oil through hose (2). Steering and fan drive system oil samples can be taken at the Scheduled Oil Sampling (S•O•S) tap (3) located on the steering solenoid and relief valve manifold.

Steering and fan drive oil from the solenoid and back-up relief valve manifold returns to the steering tank through the steering and fan drive oil return filters (4). Steering and fan drive system oil samples can also be taken at the Scheduled Oil Sampling (S•O•S) tap (5) located on the steering and fan drive oil return filter base.

An oil filter bypass switch is located on the filter base. The bypass switch provides an input signal to the Brake/Cooling ECM if the filter restriction exceeds 138 kPa (20 psi).  The Brake/Cooling ECM sends the signal to the VIMS, which informs the operator if the filters are restricted.

An oil filter bypass valve is located in the steering and fan drive oil return filter base. The bypass valve will open to protect the systems if the filters are restricted more than 345 kPa (50 psi).

Front 3512B engine module.

Shown is the right side of the front 3512B engine module.

Engine oil samples can be taken at the Scheduled Oil Sampling (S•O•S) tap (arrow) located in the tube between the engine oil cooler and the engine oil filters.

Engine oil samples for the rear 3512B engine module can be taken from the (S•O•S) tap located in the tube between the engine oil cooler and the engine oil filters.

Inspect the condition of the engine crankcase breathers (1), the coupling breather (2), and the fuel priming filters (3).  The engine crankcase and coupling breathers prevent pressure from building up in the engine and coupling housings.

Fuel only flows through the fuel priming filters when the electrical fuel priming pump is running.  Generally, the fuel priming filters do not need to be changed through the life of the engine.  Service these filters only as needed.

The right front service brake pressure can be measured at the tap (1).  The right front parking brake pressure can be measured at the tap (2).

These taps are also used when purging the air (bleeding) from the brakes. Parking brake pressure should be 4720 ± 140 kPa (685 ± 20 psi).
Service brake pressure should be 5930 ± 140 kPa (860 ± 20 psi) during a full service brake application.

Automatic lubrication injector bank

Located behind the right front tire is one of the three injector banks (1) for the automatic lubrication (grease) system.  These injectors are adjustable and regulate the quantity of grease that is injected during each cycle.

A solenoid air valve provides a controlled air supply for the automatic lubrication system.  The solenoid air valve is controlled by the Vital Information Management System (VIMS), which energizes the solenoid ten minutes after the machine is started.  The VIMS energizes the  solenoid for 75 seconds before it is de-energized. Every 60 minutes thereafter, the VIMS energizes the solenoid for 75 seconds until the machine is stopped (shut down).  These settings are adjustable through the VIMS keypad in the cab (LUBSET and LUBMAN).

Located behind the grease injector bank is the front brake cooling oil filter (2).  An oil filter bypass switch is located on the filter housing.  The front brake cooling oil filter bypass switch provides an input signal to the Brake/Cooling ECM.  The ECM sends the signal to the VIMS, which informs the operator if the filter is restricted.  Hoist and brake hydraulic system oil samples can be taken at the Scheduled Oil Sampling (S•O•S) tap located in the top center of the front brake cooling oil filter housing.

Also shown is the steering and fan drive oil cooler (3) and the two front brake oil coolers (4).

Jacket water S•O•S coolant tap

An S•O•S coolant analysis tap (1) for the jacket water cooling system is located in the oil cooler bottom tank.  Mounted on front of the hoist and brake hydraulic tank is the brake cooling pump drive motor (2).  The drive motor is used to rotate three brake cooling pumps located inside the tank (see Visual No. 20).  Brake cooling oil flows from one pump through the screen (3) to the front brakes. Brake cooling oil flows from two pumps through the screen (4) to the rear brakes. Brake cooling oil pressure can be measured at the pressure taps located on the brake cooling screen housings.

If the oil is drained from the brake cooling oil lines, the brake cooling pump drive motor must be turned ON to fill the lines with oil.  Just filling the hydraulic tank will not fill the brake cooling oil lines. The pumps in the hydraulic tank will block the oil from filling the lines. To fill the brake cooling oil lines with oil, fill the hydraulic tank with oil to the full mark in the sight gauge.  Use the brake cooling pump override option in ET to turn on the brake cooling drive pump for 10 seconds. The oil level in the hydraulic tank will lower as the brake cooling lines are filled with oil.  Refill the hydraulic tank and turn ON the brake cooling drive pump for another 10 seconds using ET. Repeat as needed to fill the brake cooling oil lines
NOTICE
Failure to correctly fill the brake cooling oil lines after an oil change may cause component damage.
Case drain filters
Located on the front of the hydraulic tank are two case drain oil filters (5). There are several piston-type pumps and motors used on the 797B truck. All piston-type pumps and motors have a small amount of leakage into  the case for cooling and lubrication. The case drain oil then returns to the lower rear hydraulic tank through the case drain oil filters.

Oil returns to the hydraulic tank through the bottom case drain filter from the following pumps and motors:
* Brake cooling motor drive pump

* Brake cooling motor

* Steering pump

Oil returns to the hydraulic tank through the top case drain filter from the following pumps and motors:
* Fan drive motor

* Fan drive motor drive pump.

Front brake cooler screen plug (arrow).
A screen for the front brake oil coolers is located behind the plug (arrow). Check the screen for plugging when required/

Brake actuation tank drain port tap.

Oil can be drained from the brake actuation and the rear axle lubrication drive tank through the pressure tap (1) located in a manifold at the rear of the hydraulic tank.

The pressure tap (1) is also used when purging (bleeding) the air from the brakes.  During the brake bleed procedure, a hose is connected to the tap to allow the bleed oil to return to the hydraulic tank (see Visuals No. 100 to 104 STMG-2).

Pressure tap (2) is used to drain trapped oil from the hydraulic lines

Lower rear tank
Shown is the 797B hydraulic tank, which is actually three separate tanks.

Lower rear tank (1) - Separately located within the large hydraulic tank is the steering system, the brake cooling drive, and the fan motor drive hydraulic tank.  The steering pumps, the brake cooling drive pump, and the fan motor drive pump all get supply oil from the lower rear hydraulic tank.

The oil level for the lower rear tank is checked at the upper sight
gauge (2) when the oil is cold and the engine is stopped.  After the engine is started, the oil level will decrease as the oil fills the steering accumulators.

After the steering accumulators are filled, the oil level should be checked again at the lower sight gauge (3).  When the engine is running and the steering accumulators are fully charged, the oil level should not be below the ENGINE RUNNING marking of the lower sight gauge (3).

If the ENGINE RUNNING level is not correct, check the nitrogen charge in both steering accumulators.  A low nitrogen charge will allow excess oil to be stored in the accumulators and will reduce the secondary steering capacity
Before removing the cap to add oil to the lower rear tank, be sure that the engine was shut off with the key start switch, and the steering oil has returned to the tank from the accumulators.

Large lower front tank - The hoist pumps and the brake cooling pumps (located in the tank) get supply oil from the large section of the tank located at the lower front.

Small top tank - The brake actuation pump and the rear axle lubrication drive pump get supply oil from a small tank section located inside of the large lower front tank.  There is a hole in the side of the small top tank that connects it to the large lower front tank.  Oil is added to the small top tank at fill tube (4). When the small top tank is full, oil flows from the hole in the small top tank to fill the large lower front tank.  The large lower front tank and the small top tank oil level is checked at the upper sight gauges (5) when the hoist cylinders are in the LOWER position.

The lower sight gauge (6) on the hoist and brake cooling hydraulic tank can be used to fill the tank when the hoist cylinders are in the RAISED position.  When the hoist cylinders are lowered, the hydraulic oil level will increase.  After the hoist cylinders are lowered, check the hydraulic tank oil level with the upper sight gauges (5).
When filling the hydraulic tanks after an oil change, fill the tanks with oil to the FULL COLD mark on the sight gauges.  Turn on the engine manual shutdown switch (see Visual No. 41) so the engine will not start.  Crank the engine for approximately 15 seconds.  The oil level will decrease as oil fills the hydraulic systems.  Add more oil to the tanks to raise the oil level to the FULL COLD mark.  Crank the engine for an additional 15 seconds.  Repeat this step as required until the oil level stabilizes at the FULL COLD mark.

Turn off the engine manual shutdown switch and start the engine. Warm the hydraulic oil. Add more oil to the tank as required to raise the oil level to the FULL WARM mark
In all three tanks, use only Transmission Drive Train Oil (TDTO) with a specification of (TO-4) or newer.
* TDTO TO-4 provides maximum frictional capability required for clutch discs used in the brakes.
* Increases brake holding capability by reducing brake slippage.
* Controls brake chatter.
* Provides maximum lubrication required for gears

Inspect the hydraulic tank and the power train breathers (7) for plugging.

NOTICE
Failure to correctly fill the hydraulic tanks after an oil change may cause component damage.

Hydraulic tanks

Shown is a sectional view of the hydraulic tank.  The hydraulic tank is actually three separate hydraulic tanks.

Lower rear tank - The steering pump, the brake cooling drive pump and the fan motor drive pump all get supply oil from a small section of the tank located at the lower rear.

Large lower front tank - The hoist pumps and the brake cooling pumps (located in the tank) get supply oil from the large section of the tank located at the lower front.

Small top tank - The brake actuation pump and the rear axle lubrication drive pump get supply oil from a small tank section located inside of the large lower front tank.  There is a hole in the side of the small top tank that connects it to the large lower front tank.  Oil is added to the small top tank and oil flows from the hole in the small top tank to fill the large lower front tank.  The purpose of the separate small top tank is to prevent brake disc material or other debris from mixing with the brake actuation oil.

Pump drive lube return screen (arrow)

The pump drive is lubricated by transmission and torque converter oil. The pump drive lubrication oil returns to the transmission sump through a screen located behind the plug (arrow).  Check the screen for plugging when required

Rear axle suspension links.
Shown are the right side rear axle suspension links (1).  The suspension links are connected to the rear axle and the main frame with pins and collets (2) that are filled with 90 weight EP oil.

The rear axle lubrication pump drive motor (3) is also shown.  The drive motor rotates the rear axle lubrication pump (4), which consists of three pump sections.  The two front pump sections pull oil from the rear axle housing through the banjo suction screen (5).

Final drives

The rear axle is equipped with double reduction planetary final drives. Rotate the final drive until the cover and plug are positioned as shown. The final drive oil level is checked and filled by removing the plug (1) in the final drive cover. The oil should be level with the bottom of the plug hole.  Fill the rear axle housing with oil before filling the final drives with oil.  Allow enough time for the oil to settle in all of the compartments. This could take as long as 20 minutes during cold temperature conditions.

The oil is drained by removing the drain plug (2).  The drain plug and the fill plug are both magnetic plugs.  The magnetic plugs should be removed from the final drives at regular intervals and checked for metal particles. If any metal particles are found, remove the axle cover and inspect the final drive for wear.

The rear axle is a common sump for the differential and both final drives. If a final drive or the differential fails, the other final drive components must also be checked for contamination and then flushed.  Failure to completely flush the rear axle after a failure can cause a repeat failure within a short time.

Use only Final Drive and Axle Oil (FDAO) with a specification of (FD-1) or Transmission Drive Train Oil (TDTO) with a specification of (TO-4) or newer.  FDAO and TDTO TO-4 oil provides:

* Maximum lubrication capability required for gears.

* Increased lubrication capability for bearings.


Check the tire inflation pressure. Operating the truck with the wrong tire inflation pressure can cause heat build-up in the tire and accelerate tire wear.

Be sure the difference between inner dual and outer dual tire pressure does not exceed 34 kPa (5 psi).  Uneven tire pressure will cause increased wheel bearing load.

NOTICE
Be sure the difference between inner dual and outer dual tire pressure does not exceed 34 kPa (5 psi).  Uneven tire pressure will cause increased wheel bearing load.

The rear axle is a common sump for the differential and both final drives.  If a final drive or the differential fails, the other final drive components must also be checked for contamination and then flushed. Failure to completely flush the rear axle after a failure can cause a repeat failure within a short time.

Failure to fill the final drives independent of the rear axle housing could result in inadequate oil fill of the final drives.  Severe component damage could result.

Rear suspension cylinders

Check the rear suspension cylinders for leaks or structural damage. Check the charge condition of the rear suspension cylinders when the truck is empty and on level ground.  Measure the charge height of the suspension cylinders and compare the dimension with the dimension that was recorded the last time the cylinders were charged.  Recharge the cylinders with oil and nitrogen if necessary.

If the rear suspension cylinders must be recharged, they must first be drained of all nitrogen and oil.  The collapsed suspension cylinder pin to pin dimension is 1120 mm (44.1 in). The normal suspension cylinder pin to pin charge height when sitting empty on level ground is approximately 1246 mm (49.1 in).

NOTE:  Refer to the June 2, 2000 Technical Information Bulletin "New Rear Strut Charging Procedure For The 797 Off-highway Truck" for the procedure to charge the rear suspension cylinders.

Automatic lubrication injector bank

The second of three injector banks (1) for the automatic lubrication (grease) system is mounted on the frame above the rear axle housing.

The rear axle housing breather (2) is located on top of the axle housing. Inspect the condition of the breather at regular intervals.  The breather prevents pressure from building up in the axle housing. Excessive pressure in the axle housing can cause brake cooling oil to leak through the Duo-Cone seals in the wheel brake assemblies.

The final drive oil filter (3) is located on the left side of the rear axle housing. An oil filter bypass switch and an oil pressure switch are located on the filter housing.  The switches provide input signals to the Brake/Cooling ECM.  The Brake/Cooling ECM sends the signals to the VIMS, which informs the operator if the final drive oil pressure is low or if the filter is restricted.

The differential oil filter (4) is located on the right side of the rear axle housing. An oil filter bypass switch and an oil pressure sensor are located on the filter housing.  The switch and sensor provide input signals to the Brake/Cooling ECM.  The Brake/Cooling ECM sends the signals to the VIMS, which informs the operator of the differential oil pressure and if the filter is restricted.

Rear axle oil level sight glass.

The rear axle oil level is checked by viewing the oil level sight glass. When the oil is cold with the engine stopped, the oil should be in the cold oil engine stopped range in the lower part of the sight glass. When the engine is started the oil level will drop below the bottom cold fill line. This is normal. Do not add oil.  When the oil temperature is above 60°C (140°F) with the engine running, the oil level should be between the top line of the cold oil engine stopped range and the top line of the warm oil engine running range.  The expected oil level is in the warm oil engine running range.

Four compartments must be filled with oil to fill the rear axle housing and final drives.

First, remove the carrier housing fill plug.  Fill the carrier housing with oil through the fill plug hole until oil shows in the carrier housing oil level sight glass.  Install the carrier fill plug.  The carrier housing is drained by removing the carrier housing magnetic drain plug

Second, remove one of the banjo housing fill covers.  Fill the banjo housing with oil through a cover hole until the oil reaches the cold oil engine stopped range in the lower part of the sight glass. The banjo housing is drained by removing the banjo housing magnetic drain plug.

After filling the banjo housing with oil, fill both final drives with oil. Rotate the final drive until the cover and oil level magnetic plug are positioned as shown.  The final drive oil levels are checked and filled by removing the magnetic plugs in the final drive covers.  The oil should be level with the bottom of the plug hole.  Allow enough time for the oil to settle in all of the compartments.  This could take as long as 20 minutes during cold temperature conditions.

The final drive oil is drained by removing the magnetic drain plug.  The drain plug and the fill plug are both magnetic plugs.  The magnetic plugs should be removed from the final drives at regular intervals and checked for metal particles.  If any metal particles are found, remove the axle cover and inspect the final drive for wear.

The rear axle is a common sump for the differential and both final drives. If a final drive or the differential fails, the other final drive components must also be checked for contamination and then flushed.  Failure to completely flush the rear axle after a failure can cause a repeat failure within a short time.

The service interval for changing the differential and final drive oil is 2000 hours.

The rear axle suction screen is located behind the cover at the bottom of the rear axle housing. Do not remove the suction screen cover unless the banjo housing oil is drained.

NOTICE
Failure to fill the final drives independent of the rear axle housing could result in inadequate oil fill of the final drives.  Severe component damage could result.

The rear axle is a common sump for the differential and both final drives.  If a final drive or the differential fails, the other final drive components must also be checked for contamination and then flushed. Failure to completely flush the rear axle after a failure can cause a repeat failure within a short time.

Cables hold body up.

The cables that hold the body up are stored below the rear of the body. Whenever work is to be performed while the body is raised, the cables must be connected between the body and the rear frame to hold the bodyin the raised position.
WARNING
The space between the body and the frame becomes a zero clearance area when the body is lowered.  Failure to install the cables can result in injury or death to personnel working in this area.

The cables will not hold if the hoist control lever is used to power down the body.  Always disconnect the hoist lever sensor connector when working below the body.

Transmission

Shown is the left side of the transmission.  The transmission magnetic scavenge screens are located in the housing (1).

The transmission control filter (2) is located at the front left side of the transmission. Transmission oil samples can be taken at the Scheduled Oil Sampling (S•O•S) tap located in the top center of the filter housing.

Two oil pressure taps are also located on top of the filter housing.  These taps can be used to measure the transmission control pressure.  The tap on the left can be used to measure unfiltered oil pressure. The tap on the right can be used to measure filtered oil pressure.  Together, these two taps can be used to determine the oil filter restriction.

An oil filter bypass switch is also located on the filter housing. The bypass switch provides an input signal to the Transmission Electronic Control Module (ECM).  The Transmission ECM sends the signal to the Vital Information Management System (VIMS), which informs the operator if the filter is restricted.

The transmission lube relief valve (3) is also located on the left side of the transmission case.  The transmission temperature sensor and the transmission lube pressure sensor are located on this valve.  The two sensors provide input signals to the Transmission ECM.  The Transmission ECM sends the signal to the VIMS, which informs the operator of the transmission temperature and lube pressur.

Fuel tank

The fuel tank is located on the left side of the truck.  The fuel level sight gauge (1) is used to check the fuel level during the walk around inspection.

Two fuel tank sizes are available:
 6822 L (1800 gallon) - 24 hours.
3866 L (1020 gallon) - 12 hours

The fuel tank size attachment code must be programmed into the VIMS with the keypad.  If the attachment code is not programmed into the system a Fuel Level F02 event will be logged in the VIMS.  Using the ATTACH (288224) parameter code, input the code that corresponds to the size of the fuel tank installed on the truck. A laptop with the VIMSpc99 software must be attached to the truck during the programming.

Fuel Tank Attachment Codes:

* 6822 L (1800 gallon) - Code 1
* 3866 L (1020 gallon) - Code 2

Also shown are the rear brake oil coolers (2).  Engine aftercooler coolant is used to cool the rear brake oil. An S•O•S coolant analysis tap (3) for the aftercooler cooling system is located in the oil cooler bottom tank.

Primary fuel screen

The primary fuel screen (1) is located on the inner surface of the fuel  tank.  Open the drain valve (2) to remove condensation from the fuel tank.

A fuel level sensor (3) is also located on the fuel tank.  The fuel level sensor emits an ultrasonic signal that bounces off a metal disk on the bottom of a float. The time it takes for the ultrasonic signal to return is converted to a Pulse Width Modulated (PWM) signal.  The PWM signal changes as the fuel level changes.  The fuel level sensor provides the input signals to the VIMS, which informs the operator of the fuel level.  A category level 1 warning (FUEL LVL LO) is shown on the VIMS display if the fuel level is less than 15%.  A category level 2 warning (FUEL LVL LO ADD FUEL NOW) is shown on the VIMS display if the fuel level is less than 10%.

The fuel level sensor receives 24 Volts from the VIMS Main Module.  To check the supply voltage of the sensor, connect a multimeter between Pins 1 and 2 of the sensor connector.  Set the meter to read "DC Volts."

The fuel level sensor output signal is a Pulse Width Modulated (PWM) signal that varies with the fuel level.  To check the output signal of the fuel level sensor, connect a multimeter between Pins 2 and 4 of the fuel level sensor connector.  Set the meter to read "Duty Cycle."  The duty cycle output of the fuel level sensor should be approximately 6% at 0 mm (0 in.) of fuel depth and 84% at 2000 mm (78.8 in.) of fuel depth.

Rear brake cooler screen plug (arrow)

A screen for the rear brake oil coolers is located behind the plug (arrow). Check the screen for plugging when required.

Torque converter and transmission oil level sight gauges

Supply oil for the torque converter and the transmission is contained in the torque converter case.  Sight gauges (1) are used to check the oil level for the torque converter and the transmission.

NOTE:  The FULL COLD oil level mark should only be used with the engine OFF.  The FULL WARM oil level mark should only be used with the engine RUNNING.

Torque converter and transmission oil is added at the fill tube (2).  When filling the torque converter and transmission oil sump after an oil change, fill the sump with oil to the top of the upper sight gauge.  Turn off the engine manual shutdown switch (see Visual No. 41) so the engine will not start.  Crank the engine for approximately 15 seconds.  The oil level will decrease as oil fills the torque converter and transmission system.  Add more oil to the sump to raise the oil level to the FULL COLD mark. Crank the engine for an additional 15 seconds. Repeat this step as required until the oil level stabilizes.

Turn off the engine manual shutdown switch and start the engine. Warm the torque converter and transmission oil. Add more oil to the sump as required to raise the torque converter and transmission oil level to the FULL WARM mark.

NOTE: Adding oil to the transmission case through the magnetic suction screen (see Visual No. 28) can reduce the time required to fill the torque converter and transmission oil sump
A power train oil level switch (not shown) is mounted on the front of the torque converter case.  The switch provides an input signal to the transmission Electronic Control Module (ECM).  The Transmission ECM sends the signal to the Vital Information Management System (VIMS), which informs the operator if the power train oil level is low.

The torque converter outlet screen (top) and the magnetic suction screen (bottom) are located behind the cover (3). Located on the cover is the torque converter oil temperature sensor and the torque converter outlet screen bypass switch.  The temperature sensor and the bypass switch provide input signals to the Transmission ECM.  The Transmission ECM sends the signal to the Vital Information Management System (VIMS), which informs the operator if the torque converter oil temperature is high or the outlet screen is plugged.

Use only Transmission Drive Train Oil (TDTO) with a specification of TO-4 or newer.

TDTO TO-4 oil provides maximum lubrication capability required for clutch discs used in transmissions and torque converters.

Use only mono-viscosity (straight weight) oils.  Multi-viscosity oils use viscosity improvers which, when subjected to shearing conditions, are reduced to the lower weight rating.  For example, when a 10W-30 oil is used in a shear condition, after time the oil will only perform to 10W specifications.

Never use engine oil in transmissions. Engine oils are formulated to minimize friction. Oils used in transmissions and torque converters must allow adequate friction to reduce slippage.

NOTE: Transmission Multi-Season (TMS) oil exceeds TDTO TO-4 specifications and is an acceptable oil to use in the transmission and torque converter sump.


NOTICE
Failure to correctly fill the torque converter and transmission oil sump or shifting out of NEUTRAL before the sump is full after an oil change may cause transmission clutch damage.

Torque converter charging filter.
Located on the right side of the torque converter housing is the torque converter charging filter.  Torque Converter oil samples can be taken at the Scheduled Oil Sampling (S•O•S) tap (1) located in the top center of the filter housing.

Two oil pressure taps (2) are also located on top of the filter housing. These taps can be used to measure the torque converter charging pressure. The tap on the left can be used to measure unfiltered oil pressure. The tap on the right can be used to measure filtered oil pressure. Together, these two taps can be used to determine the oil filter restriction.

An oil filter bypass switch (3) is located on the filter housing. The bypass switch provides an input signal to the transmission Electronic Control Module (ECM).  The Transmission ECM sends the signal to the Vital Information Management System (VIMS), which informs the operator if the filter is restricted.

Brake actuation filters.

Located inside the left frame near the torque converter are the brake actuation filters (1).  An oil filter bypass switch (2) is located on both of the oil filter bases. The bypass switches provide input signals to the Brake/Cooling ECM.  The Brake/Cooling ECM sends the signals to the VIMS, which informs the operator if the filters are restricted.

Brake actuation system oil samples can be taken at the Scheduled Oil Sampling (S•O•S) tap (3).

Rear brake cooling oil filter.

Located behind the left front suspension cylinder is the rear brake cooling oil filter (1) and the air dryers (2).

An oil filter bypass switch is located on the rear brake cooling filter housing.  The bypass switch provides an input signal to the Brake/Cooling ECM.  The Brake/Cooling ECM sends the signals to the VIMS, which informs the operator if the filter is restricted.

Hoist and brake hydraulic system oil samples can be taken at the Scheduled Oil Sampling (S•O•S) tap located in the top center of the rear brake cooling oil filter housing.

The air dryers remove contaminants and moisture from the air system. The condition of the desiccant in the air dryer should be checked every 250 hours and changed periodically (determined by the humidity of the local climate).

Air tank drain valve.

The air tank is located in front of the left front suspension cylinder.  A drain valve (1) is located in the bottom of the tank.  Drain the condensation from the air tank each morning.

The air system can be charged from a remote air supply through a ground level connector located below the air tank inside the left frame.

The grease tank (2) for the automatic lubrication system is located on the front bumper. Check the level of the grease in the tank with the grease level indicator located on top of the tank.

Engine oil filters.

Three engine oil filters are located on the left side of the front and rear engine modules.  Each engine module has a separate oil system.  Engine oil should be added at the fill tube (1) and checked with the dipstick (2) located on each engine.

The engine lubrication system is equipped with two oil pressure sensors (3).  A sensor is located on each end of the oil filter base.  One sensor measures engine oil pressure before the filters.  The other sensor
measures oil pressure after the filters.  The sensors provide input signals to the Engine Slave ECMs.  The ECMs provide input signals to the VIMS, which informs the operator of the engine oil pressure.  Together, these sensors inform the operator if the engine oil filters are restricted.

An engine oil level switch (4) provides input signals to the Engine Slave ECMs.  The Slave ECMs provide an input signal to the VIMS, which informs the operator of the engine oil level.

The oil level switch tells the operator when the engine oil level is low and it is unsafe to operate the truck without causing damage to the engine. The ENG OIL LEVEL LOW message is a Category 2 or 3 Warning.

Use only Diesel Engine Oil (DEO) with a specification of (CG-4) or newer.  DEO oil with a (CH-4) specification is available and should be used if possible.

* CH-4 engine oil requires more performance tests than previous oils, such as CE or CF, and has a narrower performance band.

* CH-4 engine oil can withstand higher temperatures before coking and has better dispersing capability for controlling soot.

* CH-4 engine oil has better fuel sulfur neutralization capability.


On both engine modules, the fitting (5) can be used to drain the engine oil that is trapped above the filters.  Do not add oil through the fitting because unfiltered oil will enter the engine.  Any contamination could cause damage to the engine.


NOTICE
When changing the engine oil filters, drain the engine oil that is trapped above the oil filters through the fitting (5) to prevent spilling the oil. Oil added to the engine through the fitting will go directly to the main oil galleries without going through the engine oil filters. Adding oil to the engine through the fitting may introduce contaminants into the system and cause damage to the engine.

Secondary fuel filters.

Two secondary fuel filters are located above the engine oil filters on the left side of the front and rear engine modules.  Each engine module has a separate fuel system.  The secondary fuel filters are 2 micron filters.  The clearances in the fuel injectors are 5 micron. Failure to use 2 micron secondary fuel filters may cause early injector failures.

Located above the fuel filters is the switch (1) that controls the electrical fuel priming pump.  A 10 amp circuit breaker (2) protects the fuel priming pump electrical circuit.  The fuel priming pump is used to fill the filters after they have been changed.

A fuel filter bypass switch (3) is located on the filter base.  The bypass switches provide input signals to the engine slave ECMs.  The engine slave ECMs send the signals to the VIMS, which informs the operator if the filters are restricted.

If fuel filter restriction exceeds 138 kPa (20 psi), a fuel filter restriction event is logged. No factory password is required to clear this event.

NOTE: If the fuel systems require priming, it may be necessary to block the fuel return line during priming to force the fuel into the injectors.

Rear engine oil S•O•S tap.

On the rear engine module, engine oil samples can be taken at the Scheduled Oil Sampling (S•O•S) tap (1).

Engine oil samples for the front 3512B engine module can be taken from the (S•O•S) tap located in the tube between the engine oil cooler and the engine oil filters (see Visual No. 12).

A spring coupling is used to connect the front and rear engine modules. The spring coupling is cooled and lubricated with oil from a separate oil compartment.  Spring coupling oil should be added at the fill tube (2) and checked with the dipstick (3). Use the same oil specification as used in the engine sumps.

The spring coupling oil system has an oil filter (4) located at the left rear of the rear engine module. Spring coupling oil system oil samples can be taken at the Scheduled Oil Sampling (S•O•S) tap (5).

Engine oil renewal system.

Engine Oil Renewal System (attachment): Located on the left side of the engine are the components of the engine oil renewal systems. There is a separate oil renewal system on the front and the rear engine modules. Shown is the front engine module.  On each engine module, engine oil flows from the engine block through an oil filter (1) to the engine oil renewal solenoid valve (2). When the solenoid is energized and
de-energized, a small amount of oil flows from the engine oil renewal solenoid valve into the fuel line that returns to the fuel tank.  The engine oil returns to the fuel tank with the return fuel.  The engine oil mixes with the fuel in the tank and flows with the fuel to the EUI injectors to be burned.

If the machine is equipped with the engine oil renewal system, the engine oil filters, the engine oil renewal system filter, the primary fuel screen, and the secondary fuel filters must all be changed at 500 hour intervals. The engine oil should be changed at least once per year or 4000 service meter hours.

Engine oil samples must be taken regularly to ensure that the soot level of the engine oil is in a safe operating range.

Manual engine shutdown switc.

Before climbing the truck ladder, make sure that the manual engine shutdown switch (1) is in the OFF position.  The engine will not start if the manual shutdown switch is in the ON position. The switch may also be used to shut down the engine from the ground level.  Do this periodically to check the secondary steering system (see Visual No. 52 STMG-2).

The toggle switches (2) control the lights in the engine compartment and above the access ladder.  The RS-232 service connector (3) is used to connect a laptop computer with VIMS-PC software to view real time data or download logged information from the VIMS.  The battery disconnect switch (4) and VIMS service connector key switch (5) must be in the ON position before the laptop computer with VIMS software will communicate with the VIMS.

The blue service lamp (6) is part of the VIMS.  When the key start switch is turned to the ON position, the VIMS runs through a self test.  During the self test, the service lamp will flash three times if there are logged events stored in the VIMS main module or once if there are no logged events.

During normal operation, the service lamp will turn ON to notify service personnel that the VIMS has an active data (machine) or maintenance (system) event.  The service lamp flashes to indicate when an event is considered abusive to the machine.

Inspect radiator

While climbing the ladder, make a thorough inspection of the radiator.  Be sure that no debris or dirt is trapped in the cores.

Located above the radiator is the cooling system shunt tank. Located on the rear platform are the five engine air filter housings.

Engine cooling systems:

The cooling system on the 797B truck is divided into two systems.  The two systems are the jacket water cooling system and the aftercooler cooling system.  These two systems are not connected. When servicing the cooling systems, be sure to drain and fill both systems separately.

The coolant levels are checked at the shunt tank.  The gauge (1) on the right is used to check the jacket water coolant level.  The gauge (2) on the left is used to check the aftercooler coolant level.  The cooling systems are protected by relief valves (3). If a cooling system overheats or if coolant is leaking from a relief valve, clean or replace the relief valve.

The water used in the cooling system is critical for good cooling system performance. Use distilled or deionized water whenever possible to prevent acids or scale deposits in the cooling system.  Acids and scale deposits result from contaminants that are found in most common water sources.

Never use water alone.  All water is corrosive at engine operating temperatures without coolant additives.  Also, water alone has none of the lubrication properties which are required for water pump seals.

The 797B is filled at the factory with Extended Life Coolant (ELC).  If ELC is maintained in the radiator, it is not necessary to use a supplemental coolant additive.  If more than 10% of conventional coolant is mixed with the ELC, a supplemental coolant additive is required.

Large primary element

Two filter elements are installed in the filter housings.  The large element is the primary element and the small element is the secondary element.

Air intake system tips:
* The primary element can be cleaned a maximum of six times.
* Never clean the secondary element for reuse.  Always replace the secondary element.
* Air filter restriction causes black exhaust smoke and low power.
* A .6°C (1°F) increase in intake temperature increases exhaust temperature 1.8°C (3°F).
* For every 250 mm (10 in.) of water restriction above 500 mm (20 in.) of water in an air filter, the inlet temperature increases 60°C (100°F).
* Exhaust temperature should not exceed 750°C (1382°F).

Located below the air filter housings are the air filter dust valves (arrow). Check the dust valves for plugging.  If necessary, disconnect the clamp and open the cover for further cleaning.

The dust valve is OPEN when the engine is OFF and closes when the engine is running.  The dust valve must be flexible and close when the engine is running or the precleaner will not function properly and the air filters will have a shortened life.  Replace the rubber dust valve if it becomes hard and not flexible.

Air induction system

An air induction system that is free of air leaks is essential to the health of the engine.  Air leaks in the air induction system can allow contaminants to enter the engine.

In order to pressurize the air induction system, the area around the filters must be blocked.  Shown is the fabricated tooling installed to test the air induction system. This procedure detects leaks by blocking the air intake ducts, pressurizing the system, and spraying a soap solution. Maintain the air pressure at 14 + 0 - 7 kPa (2 + 0 - 1 psi) during the test.

Use this procedure to inspect the air induction system if any of the following events occur:
* Assembly of a new machine
* Installation or removal of the engine
* Elevated levels of iron, chrome, or silicon in the S•O•S report
* Removal and Installation of components of the air induction system
* Damage to the air cleaner group or the air induction system

Ether cylinder solenoids (arrow)

The ether cylinder solenoids (arrow) are located in the engine compartment behind the radiator.  Make sure the ether cylinders are not empty.

The Engine ECM will automatically inject ether from the ether cylinders during cranking. The duration of automatic ether injection is dependent on jacket water coolant temperature.  The duration will vary from 10 to 130 seconds.

The operator can also inject ether manually with the ether switch in the cab on the center console (see Visual No. 61).  The manual ether injection duration is 5 seconds.

Ether will be injected only if the engine coolant temperature is below 10°C (50°F) and engine speed is below 1900 rpm.

Ether starting tips:
* Cold weather causes rough combustion and white exhaust smoke from unburned fuel. Ether injection will reduce the duration and severity of unburned fuel symptoms.

Hoist screens.

Located inside the right frame near the transmission are the two hoist screens (1).  An oil filter bypass switch (2) is located on the screen base. The hoist screen bypass switches provide an input signal to the Chassis ECM.  The Chassis ECM sends the signals to the VIMS, which informs the operator if the screens are restricted.

Parking brake accumulator and Service brake accumulator.

Located inside the left frame near the transmission is the parking brake accumulator (1) and the service brake accumulator (2). The nitrogen charge pressure for both charge accumulators is 10335 ± 345 kPa (1500 ± 50 psi) at a temperature of 21°C (70°F).  The accumulators are charged through a fitting located behind the cap on top of the accumulators.

To charge the brake accumulators, use the 175-5507 Nitrogen Charging Group and the 152-2023 Accumulator Charging Group.

The nitrogen charge in all three accumulators should be checked every 3 months or 500 hours.

Windshield washer reservoir.

The windshield washer reservoir (1) is located in the compartment in front of the cab.  Keep the reservoir full of windshield washer fluid.

The air conditioner filter (2) is also located in the compartment in front of the cab. Clean or replace the filter element when a reduction of circulation in the cab is noticed.

10 hours/daily checks performed in the operator's cab.

The remaining 10 Hours or Daily checks are performed in the operator's compartment.  They are as follows:

* Brakes:  Check operation
* Indicators and gauges:  Test operation
* Seat belt:  Inspect
* Back-up alarm:  Test operation
* Secondary steering:  Test operation


The brakes are checked by engaging one of the brake systems and placing the shift lever in FIRST FORWARD. Accelerate the engine until the truck moves. The truck must not move below 1200 rpm.  This procedure should be repeated for each brake lever or pedal.

See the Operation and Maintenance Manual for more information on the remaining tests performed in the cab.

The cab fresh air filter is located behind the cover (arrow). Clean or replace the cab fresh air filter when necessary.

Ambient temperature sensor (arrow).

Located in the center of the front radiator grill is the ambient temperature

sensor (arrow). The ambient temperature sensor provides input signals to
the VIMS Main Module.
The service technician can use the ambient temperature sensor input as an
indication of the ambient temperature when investigating temperature
related problems on the machine.

Ambient temperature sensor supply voltage.
The ambient temperature sensor receives a regulated 8.0 ± 0.5 Volts from
the VIMS Main Module. To check the supply voltage of the sensor,
connect a multimeter between Pins A and B of the sensor connector. Set
the meter to read "DC Volts."

Ambient temperature sensor signal is PWM.
The ambient temperature sensor output signal is a Pulse Width Modulated
(PWM) signal that varies with temperature. To check the output signal of
the ambient temperature sensor, connect a multimeter between Pins B and
C of the ambient temperature sensor connector. Set the meter to read
"Duty Cycle." The duty cycle output of the ambient temperature sensor
should be between 10 and 93% with an operating temperature range
between -40°C (-40°F) and 135°C (275°F).

Grease autolube pressure sensor (arrow).

Located above the rear axle is the (grease) autolube pressure sensor (arrow). The autolube pressure sensor provides input signals to the VIMS Main Module. The autolube pressure sensor is installed in the high pressure grease line that flows to the three autolube injector banks.

During a grease cycle (grease autolube solenoid is energized), if the autolube pressure is below 13700 kPa (1990 psi), the VIMS will inform the operator of an AUTO LUBE PRES LO condition. Normally, low grease pressure is an indication that the grease tank on the front bumper is empty.

Lube pressure HIGH warning.
When VIMS is not initiating a grease cycle (grease autolube solenoid is NOT energized), if the autolube pressure is above 3448 kPa (500 psi), the VIMS will inform the operator of an AUTO LUBE PRES HI condition.

The autolube pressure sensor receives 24 Volts from the VIMS Main Module. To check the supply voltage of the sensor, connect a multimeter between Pins A and B of the sensor connector. Set the meter to read "DC Volts." The autolube pressure sensor output signal is a Pulse Width Modulated (PWM) signal that varies with pressure. To check the output signal of the autolube pressure sensor, connect a multimeter between Pins B and C of the autolube pressure sensor connector. Set the meter to read "Duty Cycle." The duty cycle output of the autolube pressure sensor
should be between 5 to 15% with an operating pressure of 0 kPa (0 psi) and between 55 to 65% with an operating pressure of 20670 kPa (3000 psi).

PMS suspension cylinder pressure  sensor (arrows).

Located on all four suspension cylinders is a Truck Production Management System (TPMS) pressure sensor (arrows). The suspension cylinder pressure sensor is commonly referred to as a "strut sensor."
When the truck is being loaded, the strut sensors convert the change in pressure to a change in frequency signal. The frequency signals are then sent to the VIMS Main Module. VIMS converts the frequency signals to tons. During LOADING, the payload weight is shown on the VIMS message center display in metric or US tons.

The strut sensors receive 24 Volts from the VIMS Main Module. To check the supply voltage of the sensors, connect a multimeter between Pins A and B of the sensor connector. Set the meter to read "DC Volts.“

The strut sensors send frequency output signals to the VIMS Main Module. To check the output signal of the strut sensors, connect a multimeter between Pins B and C of the strut sensor connector. Set the meter to read "Frequency.“

797B alternators (arrows)

The 797B has two 75 amp alternators (arrows) installed on the front engine module. The "R" terminal on one of the alternators provides a voltage and a frequency input to the VIMS Main Module. The other alternator provides an input to the Chassis ECM.

The 797B has two 75 amp alternators (arrows) installed on the front engine module. The "R" terminal on one of the alternators provides a voltage and a frequency input to the VIMS Main Module he other alternator provides an input to the Chassis ECM.

Normal voltage from the alternator "R" terminal should be between 12.4 and 14.75 DC Volts. The corresponding output from the alternator + battery terminal should be approximately 2X the "R" terminal value (24.8 to 29.5 DC Volts).


The frequency from the alternator "R" terminal should be greater than 94 Hz ± 10%. A frequency less than 94 Hz is an indication that the speed of the alternator is low. The probable cause is a slipping belt, loose pulley, or an internal alternator problem.

Approximately 10 different system voltage events can be shown on the VIMS message center display. The events can be a category level 1 or 3 depending on the severity of the problem.

THANK YOU FOR YOUR VISITED