Upgrade Procedure For The 793D Off-Highway Truck Steering Accumulator {1408, 4331, 5077} Caterpillar

Off Highway Truck

793D (S/N: FDB1-UP)

Introduction

This Special Instruction provides directions to replace the bladder accumulators with the piston accumulators on the 793D trucks.

Note: Cleanliness is an important factor. Before the disassembly procedure, the exterior of the component should be cleaned. Clean components will help to prevent dirt from entering the internal mechanism.

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Personal injury can result from hydraulic oil pressure and hot oil. Hydraulic oil pressure can remain in the hydraulic system after the engine has been stopped. Serious injury can be caused if this pressure is not released before any service is done on the hydraulic system. Make sure all of the work tools have been lowered to the ground, and the oil is cool before removing any components or lines. Remove the oil filler cap only when the engine is stopped, and the filler cap is cool enough to touch with your bare hand.

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Hot oil and hot components can cause personal injury. Do not allow hot oil or hot components to contact skin. At operating temperature, the engine coolant is hot and under pressure. Steam can cause personal injury. Check the coolant level only after the engine has been stopped and the cooling system pressure cap is cool enough to touch with your bare hand. Remove the cooling system pressure cap slowly to relieve pressure. Cooling system conditioner contains alkali. Avoid contact with the skin and eyes to prevent personal injury.

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Personal injury can result from the sudden release of high pressure oil. Be sure the engine has been shut off for a minimum of five minutes to ensure that the accumulator pressure is zero. The accumulator is filled with dry nitrogen. Do not loosen or remove the valve or the cap from the top of the accumulator.

Required Tooling

Required Parts

Bladder Steering Accumulator Removal

Illustration 1	g01743373
View of Accumulator Group

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Personal injury can result from the sudden release of high pressure oil. Be sure the engine has been shut off for a minimum of five minutes to ensure that the accumulator pressure is zero. The accumulator is filled with dry nitrogen. Do not loosen or remove the valve or the cap from the top of the accumulator.

Note: Cleanliness is an important factor. Before the disassembly procedure, the exterior of the component should be cleaned. Clean components will help to prevent dirt from entering the internal mechanism.

Note: Put identification marks on all hose assemblies and on all tube assemblies for installation purposes. Plug all hose assemblies and all tube assemblies, to prevent fluid loss and contaminants from entering the system.

1. Turn the wheels to the right.

2. Apply the parking brakes.

3. Shut off the machine.

4. Release the oil pressure from the steering accumulators. Refer to Operation and Maintenance Manual, SEBU7792, "Steering Accumulator Pressure - Release".

5. Release the nitrogen charge from the steering accumulator. Refer to Steering Systems Operation/Testing and Adjusting, "Steering Accumulator - Test and Charge" for the proper procedure.

6. Drain the steering hydraulic oil into a suitable container for storage or disposal. Refer to Operation and Maintenance Manual, SEBU7792, "Steering System Oil - Change" to collect the fluids properly. For more information, check the Special Instruction, REHS1841, "General Welding Procedures".
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   Illustration 2	g01866675

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   Illustration 3	g02264599
   General view of the use of the lifting bracket and sleeve

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   Illustration 4	g03795248
   View of the lower steering accumulators

7. Remove two 205-0224 Steering Accumulator Gp (A). Use tooling (1) and tooling (2) to remove accumulators (A). Use a suitable lifting device when removing accumulators (A). Accumulators (A) weight approximately 110 kg (243lb). 9U-5980 Lifting Clamp (B), and two FT3050 Accumulator Sleeve (C) to lift accumulator group (A). Remove and retain sensor assembly (D).
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   Illustration 5	g03795261

8. Remove the tie down bracket (E).

Frame Modifications

Illustration 6	g02097614

1. Use a torch to remove bracket assembly (A). remove bracket assembly (B). For more information, check the Special Instruction, "General Welding Procedures".
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   Illustration 7	g01766394
   View of the removal of the brackets and boss

2. Grind the welds smooth to the frame.
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   Illustration 8	g02097634
   View of the frame with the old bracket

3. Remove the upper bracket.
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   Illustration 9	g01766593
   View of the frame with the upper bracket that is removed

4. Grind the welds smooth to the frame.
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   Illustration 10	g01766614
   View of frame with new bracket that is installed

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   Illustration 11	g01766794
   View of the location of upper bracket (A) 198 mm (7.795 inch)

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   Illustration 12	g01776561
   View of the location of upper bracket (B) 625 mm (24.606 inch)

5. Install upper bracket (1). Install upper bracket (1) 198 mm (7.795 inch) from the outer edge of the upright to upper bracket (1). Install upper bracket (1) 625 mm (24.606 inch) from the bottom of upper bracket (1) to the weld joint.
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   Illustration 13	g01776673
   View of the location of blocks (2) ( C) 214 mm (8.425 inch) (D) 329.5 mm (12.972 inch)

   Note: Dimension (D) is a nominal dimension which may vary by the machine.

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   Illustration 14	g01794915
   (E) 178.2 mm (7.01573 inch) (F) 330.2 mm (12.99997 inch) (G) 101.6 mm (3.99999 inch)

6. Make the appropriate measurements to locate blocks (2). Refer to Illustration 13 and Illustration 14 to view the correct measurements for the placement of blocks (2).
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   Illustration 15	g01770973

7. Install blocks (2) to plate assembly (3) with bolts (4) and washers (5) to achieve the correct alignment.

8. Place plate assembly (3) and blocks (2) in the correct locations to install the accumulators.

9. Tack weld blocks (2) to the frame.
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   Illustration 16	g01770995

10. Remove plate assembly (3) to finish weld blocks (2) to the frame.

11. Attach plate assembly (3) to blocks (2) with bolts (4) and washers (5). Torque the bolts (4) to 100 ± 20 N·m (74 ± 15 lb ft).

Installation Procedure Of The Steering Accumulators

Note: Use an appropriate lifting device to install the steering accumulators. Each accumulator weighs 118 kg (260 lb).

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Illustration 17	g02265053

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Illustration 18	g02264974

1. Pick up one accumulator group (1). Use a suitable lifting device to lift accumulator group (1). Use three 138-7575 Link Bracket (A), three 0S-1629 Bolt (B) and three 8T-4223 Hard Washer (C). The 138-7575 Link Bracket will be installed to accumulator (1).
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   Illustration 19	g03794699
   View of the accumulator group

2. Put accumulators (1) into the correct location, so that the charging ports on the top of accumulator (1) face the centerline of the truck. Assemble the two corresponding bracket assemblies (2) around accumulator (1).

   Note: Be sure that accumulator group (1) remains seated on the bracket assembly when clamp (3) is assembled.

3. Attach bracket assembly (2) to lower bracket with six bolts (4) and six washers (6). Torque bolts (4) to 100 ± 20 N·m (74 ± 15 lb ft).

4. Attach bracket assembly (2) to upper bracket with six bolts (4) and six washers (6). Torque bolts (4) to 100 ± 20 N·m (74 ± 15 lb ft).

5. Attach clamps (3) to bracket assembly (2) on upper and lower plate assemblies using two bolts (5) and two washers (6) on each clamp. Torque clamps to 100 ± 20 N·m (74 ± 15 lb ft).

Installation Of The Steering Lines

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Illustration 20	g03794788
A view of the lower steering accumulator group

1. Install One O-ring tee (1) to the piston accumulator on the left, and two O-Ring seals (13) and one O-Ring seal (14).

2. Install one connector assembly (2) to the piston accumulator in the middle.

3. Install one elbow assembly (3) to the piston accumulator on the right.
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   Illustration 21	g01861340

4. Install hose assembly (4) to tee (1).

5. Install hose assembly (5) to connector assembly (2).

6. Install hose assembly (6) to elbow assembly (3) and O-ring tee (1).
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   Illustration 22	g03794889

7. Use two bolts (10), four washers (11) and two nuts (12) to install grommet (7) to hose assembly (4) and hose assembly (5) with clip (8) and clip (9).

8. Attach hose assembly (4) to the steering valve.

9. Attach hose assembly (5) to the steering valve with one O-Ring seal (15).
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   Illustration 23	g03795278
   A view of the lower accumulator

10. Reinstall 307-6719 Pressure Switch (A) using O-Ring seal (16).
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    Illustration 24	g03795854
    A view of the backside of the lower steering accumulator group

11. Route the harness for 307-6719 Pressure Switch (A) and secure in place using one clip (17), one clip (18), two hard washers (19), and two bolts (20).

Steering Accumulator Test and Charge

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Personal injury can result from hydraulic oil pressure and hot oil. Hydraulic oil pressure can remain in the hydraulic system after the engine has been stopped. Serious injury can be caused if this pressure is not released before any service is done on the hydraulic system. Make sure all of the work tools have been lowered to the ground, and the oil is cool before removing any components or lines. Remove the oil filler cap only when the engine is stopped, and the filler cap is cool enough to touch with your bare hand.

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Dry nitrogen is the only gas approved for use in the accumulators. The charging of oxygen gas in an accumulator will cause an explosion. An explosion can be eliminated by using nitrogen gas cylinders with standard CGA (Compressed Gas Association, Inc.) No. 580 connectors. When nitrogen gas is ordered, make sure to order the cylinders with CGA No. 580 connectors. Do not rely on color codes or other methods of identification to tell the difference between nitrogen and oxygen cylinders. In any application, never use an adapter to connect your nitrogen charging group to a valve outlet used on both nitrogen, oxygen, or other gas cylinders. BE SURE YOU USE DRY NITROGEN (99.8% purity).

Stop the engine. Release the oil pressure in the steering system.

Reference: Refer to Hydraulic System Operation, Testing and Adjusting, "Steering System Pressure - Test and Adjust" for the machine that is being serviced.

To ensure that the nitrogen charge is correct, the piston for the steering accumulator must be at the bottom of the accumulator cylinder. Nitrogen gas pressure varies with the temperature. To obtain the most accurate nitrogen charge, the temperature of the accumulator must be identical to the air temperature around the accumulator.

If an accumulator has less than half of the required amount of precharge pressure, the accumulator should be charged. Charge the accumulators again after operating the steering system. The second charge prevents trapping a quantity of oil in the accumulator which will give an inaccurate precharge reading.

However, the temperature of the accumulator could be higher than the air temperature around the accumulator. In this case, the temperature of the accumulator should be used instead of the surrounding air temperature.

Note: An accumulator precharge pressure of 6550 kPa (950 psi) is required for an accumulator with an ambient air temperature of 21°C (70°F). Use the following table to adjust the pressures for other ambient conditions, as required.

Do not use an adapter to connect the nitrogen charging equipment to a valve that can be used on oxygen cylinders or gas cylinders. Use dry nitrogen.

Check that the engine has not been running for at least 5 minutes to allow the oil level in the steering accumulators to decrease. This will ensure that the pressure of the nitrogen charge is correct.

The steering accumulator has a dry charge of 6550 ± 350 kPa (950 ± 50 psi).

Test Procedure

1. Cycle the steering system to release any oil pressure that may be in the steering accumulators.
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   Illustration 25	g01259556
   Steering accumulator (1) Cap (2) Cover

2. Remove cover (2) from the steering accumulator. Remove cap (1) from the valve assembly on the steering accumulator.
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   Illustration 26	g00907670
   Parts from the nitrogen charging group (3) Valve (4) Pressure gauge (5) Chuck (6) Valve handle

3. Use a 0 kPa to 13800 kPa (0 psi to 2000 psi) pressure gauge (4) to check the nitrogen charge in the steering accumulator.

4. Ensure that valve (3) is closed. Install chuck (5) onto the nitrogen charging valve for the steering accumulator.

5. Turn valve handle (6) on chuck (5) completely in the clockwise direction. Check the temperature of the air around the steering accumulator. The reading on the pressure gauge must be within the tolerances in Table 9.

6. If the reading on the pressure gauge is too high, slowly open valve (3) to lower the pressure. If the reading on the pressure gauge is too low, use the following procedure to charge the steering accumulator.

Charge Procedure

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Illustration 27	g00907671
Nitrogen charging group (3) Valve (4) Pressure gauge (5) Chuck (6) Valve handle (7) Pressure gauge (8) Chuck for the nitrogen cylinder valve (9) Regulator assembly (10) Pressure regulating screw

1. Connect a hose from the nitrogen cylinder to valve (3).

2. Close valve (3) and open the valve on the nitrogen cylinder. Adjust screw (10) on regulator assembly (9) until pressure gauge (7) is at the correct charging pressure. Refer to Table 9 for the correct charging pressure.

3. Open valve (3) and charge the steering accumulator. Then, close valve (3). If pressure gauge (4) and pressure gauge (7) show that the same reading and the readings do not change, the accumulator charge is correct.

   If the pressure reading on gauge (4) decreases, open valve (3) and allow more nitrogen to fill the steering accumulator.

   Perform this procedure until pressure gauge (4) and pressure gauge (7) show the same reading. Make sure that neither reading changes when valve (3) is closed.

4. Close valve (3). Close the valve on the nitrogen cylinder.

5. Turn valve (6) on chuck (5) outward in the counterclockwise direction. Remove the test equipment.

Charge Procedure for a New Accumulator or Rebuilt Accumulator

Remove all the air from the nitrogen chamber of the steering accumulator. When the steering accumulator is new or rebuilt, put approximately 1.9 L (2 qt) of SAE 10W oil in the nitrogen end of the accumulator. This oil will help purge air from the nitrogen chamber of the steering accumulator. The oil will also lubricate the top seal of the accumulator piston. After the accumulator is installed on the machine, charge the accumulator with the procedure that follows:

1. Use the same equipment that is used to check the nitrogen charge in the steering accumulator.

2. Install chuck (5) onto the nitrogen charge valve for the steering accumulator.

3. Turn valve handle (6) on chuck (5) completely in the clockwise direction. Open valve (3).

4. Start the engine and run the engine until the engine reaches normal operating temperature. As hydraulic oil goes into the bottom of the steering accumulator, the air and the oil will be pushed out through the test equipment. When the oil flow stops, the top of the steering accumulator will be free of air.

5. Close valve (3) completely.

6. Stop the engine. Release the braking system oil pressure. When there is no nitrogen charge in the steering accumulator, the piston in the steering accumulator will be at the top of the accumulator cylinder.

   Reference: Refer to Hydraulic System Operation, Testing and Adjusting, "Steering System Pressure - Test and Adjust" for the machine that is being serviced.

   Note: Refer to Testing and Adjusting, RENR8336, "Accumulator (Steering) Test and Charge" for accumulator charging information.

7. Put a charge of nitrogen into the steering accumulator. Follow the procedure in Steps 1 through 5 in "Charge Procedure". The time to complete charging of the accumulator will be extended to move the accumulator piston to the bottom of the accumulator cylinder. Charging time will also be extended to allow time to purge the oil from the steering accumulator.

Installation of Eye

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Illustration 28	g02097900
View of the location of eye (tie down) (1) ( 1) eye (tie down) (W1) 8 mm (0.315 inch) fillet weld with 1.5 mm (0.06 inch) (A) 375 ± 5 mm (14.76 ± 0.197 inch) (B) 156.6 ± 5 mm (6.17 ± 0.197 inch)

1. Prepare the area that is shown in Illustration 28 to install eye (tie down) (1).
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   NOTICE
   Do Not Lift the Machine Using Eye (tie down) (1).

2. Install eye (tie down) (1). Refer to Illustration 28 to view the location of eye (1).

   Note: Eye (1) is a tie down location.

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   Illustration 29	g06017922
   View of film

3. Install film (2) onto frame next to eye (tie down) (1).