789D and 789D XQ Off-Highway Truck Power Train Caterpillar

Transmission Hydraulic Control Primary Clutch Pressure - Test and Adjust

Usage:

789D SHH

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Table 1
Tools Needed
Part Number	Part Description	Qty
8T-5200	Generator and Counter Signal Group	1
6V-6064	Transmission Test Cover⁽¹⁾	1
FT-1775	Transmission Test Cover⁽¹⁾	1
8T-0854	Pressure Gauge 0 to 1000 kPa (0 to 150 psi)	1
177-7862	Hose Assembly	6
6V-4143	Coupler	12
9S-1721	Socket Extension	1
9U-6635	Ratchet	1

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⁽¹⁾	Only one type of transmission test cover is necessary.

Note: An 8T-5200 Signal Generator/Counter can be used to shift the transmission during the diagnostic tests instead of manual shifting.

Note: Make sure that the filters and the screens are clean before you test any pressures. Make sure that the oil is at operating temperature before you perform this test.

This test will determine if the clutch pressures are correctly adjusted.

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Personal injury or death can result from sudden machine movement.
Sudden movement of the machine or release of air pressure or oil pressure can cause injury to persons on or near the machine.

To help prevent possible injury before testing and adjusting any air system or hydraulic system, perform the procedure in the Testing and Adjusting, "General Information" section.

Procedure

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NOTICE

Make sure the drive axles are removed or disconnect the drive shaft from the machine for this test or the clutches of the transmission will be damaged.

Remove the drive axles from the machine or disconnect the drive shaft from the machine.
Note: Failure to perform Step 1 can result in damage to the transmission clutches.
If a 6V-6064 Transmission Test Cover is used, remove the large cover from the top of the transmission case. If an FT1775 Transmission Test Cover is used, remove the smaller cover from the transmission case.
Remove six load piston plugs (33).

Reinstall the test cover. Install four bolts to hold the test cover in place.

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Illustration 1	g00398738
Installation of the test gauge for pressure (A) Pressure tap for the No. 2 clutch (B) Pressure tap for the No. 1 clutch (C) Pressure tap for the No. 3 clutch (D) Pressure tap for the signal pressure for the dual stage relief valve (E) Pressure tap for the No. 4 clutch (F) Pressure tap for the No. 5 clutch (G) Pressure tap for the No. 6 clutch (H) This pressure tap is not used. (M) Pressure tap for the pilot oil of the transmission hydraulic control

Install two 6V-4143 Couplers, 177-7862 Hose Assembly and 8T-0854 Pressure Gauge to the nipples at pressure taps (A), (B), (C), (E), (F), and (G).
Start the engine. Run the engine at the low idle rpm with the transmission in NEUTRAL-1.
Record the pressures on the gauges. Use Table 3 to record the measurements.
Use a 9U-6635 Reversible Ratchet and a 9S-1721 Extension (1/4 inch square drive) to move the transmission rotary selector spool to the NEUTRAL-2 position. Refer to the procedure for manual shifts in the Testing and Adjusting, "Transmission Hydraulic Control Clutch Pressure - Test".
Note: An 8T-5200 Signal Generator/Counter can be used to shift the transmission during the diagnostic tests instead of manual shifting.
Record the pressures on the gauges. Use Table 3 to record the measurements.
Manually shift the transmission into REVERSE and into all the forward speeds. Record the pressures on the gauges during each shift.
Stop the engine with the transmission rotary selector spool in NEUTRAL-1.
Compare the actual primary clutch pressure that is recorded on Table 3 and the pressure for each clutch that is provided in Table 3.
After the pressures are correctly set, remove the pressure gauges and the test cover. Install load piston plugs (33).
Install the large cover, the small cover, and the solenoid guard. Use new gaskets when installing all covers. Connect the wiring harness to the solenoids.
Note: After the primary pressures are set, the maximum clutch pressures must be set. Perform the Testing and Adjusting, "Transmission Hydraulic Control Clutch Pressure - Test".
Install the drive axles on the machine or install the drive shaft from the machine.

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Table 2
Speed	N-1	N-2	R	1	2	3	4	5	6
Engaged Clutches	3	1	1, 6	1, 5	2, 5	1, 4	2, 4	1, 3	2, 3
Stations	"C"	"B"	"B", "G"	"B", "F"	"A", "F"	"B ", "E"	"A", "E"	"B", "C"	"A", "C"

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Table 3
Measurements of the Primary Clutch Pressure
Station⁽¹⁾	"A"	"B"	"C"	"D"⁽²⁾	"E"	"F"	"G"
Low Idle Pressure⁽³⁾	555 kPa (80 psi)	587 kPa (85 psi)	548 kPa (79 psi)	N/A	506 kPa (73 psi)	480 kPa (70 psi)	488 kPa (71 psi)
Actual				N/A

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⁽¹⁾	Station "H" is not used.
⁽²⁾	Station "D" does not control a clutch. Station "D" controls the dual stage relief valve for the system pressure.
⁽³⁾	The tolerance is ± 41 kPa (± 6 psi).

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Illustration 2	g00485627
Pressure control valve (28) Modulation reduction valves (seven) (29) Selector piston plugs (seven) (30) Load piston orifice (31) Decay orifice plugs (five) (32) Shims (seven places) (33) Load piston plugs (six) (34) Inner springs (six) (35) Outer springs (seven) (36) Load piston (37) Selector piston

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Table 4
Specifications and Identification of the Components of the Pressure Control Valve
Location of the Load Piston Body⁽¹⁾	A	B	C	D	E	F	G
Thickness of the Load Piston Orifice	4.58 mm (.180 inch)	2.54 mm (.100 inch)	2.54 mm (.100 inch)		2.54 inch (.100 inch)	6.60 mm (0.260 inch)	6.60 mm (.260 inch)
Color of the Outer Spring of the Load Piston	Light green color	Yellow color	Light green color		Light green color	Light green color	Light green color
Color of the Inner Spring of the Load Piston	Light blue color	Light blue color	Light blue color		Orange color	Yellow color	Light green color
Size of the Decay Orifice	1.40 mm (0.055 inch)	1.57 mm (0.062 inch)	1.98 mm (0.078 inch)		1.57 mm (0.062 inch)	1.40 mm (0.055 inch)
Color of the Decay Orifice	Yellow color	Green color	Red color		Green color	Yellow color

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⁽¹⁾	The location of the load piston body is identical to the location of the station for the valve. Station "H" is not used.

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Table 5
(1) Shims for the Pressure Control Valve Pressure Change per Shim
Station⁽¹⁾	A	B	C	D⁽²⁾	E	F	G
Engaged Clutch	2	1	3	-	4	5	6
Thickness of Shim	Pressure Change	Pressure Change	Pressure Change	Pressure Change	Pressure Change	Pressure Change	Pressure Change
5J-2721 Shim
0.13 mm (0.005 inch)	20 kPa (2.9 psi)	17 kPa (2.4 psi)	20 kPa (2.9 psi)	12 kPa (1.7 psi)	17 kPa (2.5 psi)	19 kPa (2.7 psi)	19 kPa (2.8 psi)
6J-3993 Shim
0.25 mm (0.010 inch)	41 kPa (5.9 psi)	33 kPa (4.8 psi)	41 kPa (5.9 psi)	25 kPa (3.6 psi)	35 kPa (5.1 psi)	37 kPa (5.4 psi)	39 kPa (5.6 psi)
4M-1751 Spacer
0.41 mm (0.016 inch)	65 kPa (9.4 psi)	53 kPa (7.7 psi)	65 kPa (9.4 psi)	39 kPa (5.7 psi)	56 kPa (8.1 psi)	59 kPa (8.6 psi)	62 kPa (9.0 psi)
5J-1036 Shim
0.80 mm (0.031 inch)	125 kPa (18.2 psi)	103 kPa (15.0 psi)	125 kPa (18.2 psi)	76 kPa (11.0 psi)	109 kPa (15.8 psi)	114 kPa (16.6 psi)	120 kPa (17.4 psi)

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⁽¹⁾	Station "H" is not used.
⁽²⁾	Station "D" does not control a clutch. Station "D" controls the dual stage relief valve for the system pressure.

Problem: The primary pressure is correct, but the maximum pressure is not correct.

Probable Cause

The load piston springs (34) and (35) are weak or incorrect. Replace the load piston springs.

Problem: The pressure at one clutch is 0 kPa (0 psi).

Probable Cause

Selector piston plug (29) is not installed.
The selector piston (37) is stuck.
The modulation reduction valve (28) is stuck.

Selector piston (37) is stuck.
Inner spring (34) is weak or broken, and/or outer spring (35) is weak or broken.
Incorrect inner spring (34) and/or outer spring (35).
The primary pressure is set incorrectly. Add shims (32). Refer to Table 5.

Problem: The primary pressure at one clutch is too high.

Probable Cause

Incorrect inner spring (34) and/or outer spring (35).
The primary pressure is set incorrectly. Remove shims (32). Refer to Table 5.

Problem: An additional clutch receives pressure oil in certain speeds.

Probable Cause

Decay orifice (31) is plugged.
The drain orifice in the return end of the rotary selector spool is plugged.
A selector piston (37) is stuck.
A load piston (36) is stuck.
A modulation reduction valve (28) is stuck.

Problem: The pressure in one clutch at the high idle rpm is not correct, but the primary pressure in the same clutch is correct.

Probable Cause

Wrong inner spring (34) and/or outer spring (35) is installed in the load piston.
Inner spring (34) and/or outer spring (35) in the load piston is weak or broken.
Load piston orifice (30) is plugged.