621H, 623H and 627H Wheel Tractor-Scrapers Power Train Caterpillar

Synchronizing Valve Pressure - Test and Adjust - Rear Power Train

Usage:

627H DBW

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Table 1
Synchronizing Valve Pressure
Date	Equipment ID Code
	Pressure Specifications			Actual
	Test Port (2)	Test Port (3)	Test Port (4)
Low Idle	96 ± 7 kPa (14 ± 1 psi)	0± 0kPa (0 ± 0 psi)	690 ± 35 kPa (100 ± 5 psi)
High Idle			2070 ± 30 kPa (300 ± 4 psi)
High Idle⁽¹⁾			910 kPa (132 psi)

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⁽¹⁾	With solenoid (2) disconnected

This test will determine if the synchronizing solenoid and the priority valve are operating correctly.

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Illustration 1	g02571852
Tooling (A) 198-4240 Digital Pressure Indicator Gp

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Table 2
Tool	Item	Qty	Part No	Description
A			198-4240	Digital Pressure Indicator Gp
	A1	1	198-4234	Digital Indicator
	A2	3	198-4237	Pressure Sensor Gp (0 to 3,445 kPa (0 to 500 psi))
	A3	3	198-4236	Adapter Cable As

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Illustration 2	g03632456
Lockup Clutch and Synchronizing Valve (1) Synchronizing solenoid (2) Pressure tap for the torque converter inlet (3) Pressure tap for the lockup clutch (4) Pressure tap for the charging pump at the lockup clutch and synchronizing valve

Remove the plugs from pressure tap (2), pressure tap (3), and pressure tap (4). Install Tool (A2) into each of the pressure taps. Attach Tool (A3) to each of the adapters.
Connect Tooling (A) to pressure tap (2), pressure tap (3), and pressure tap (4).

Start the engines and run the engines at LOW IDLE rpm in the NEUTRAL position.
Move the rotary selector spool to the FIRST SPEED position. Keep the engines at LOW IDLE rpm.
Disconnect the wiring harness to the synchronizing solenoid.
The pressure on the digital indicator at pressure tap (4) must be 690 ± 35 kPa (100 ± 5 psi). The pressure on the digital indicator at pressure tap (2) must be 96 ± 7 kPa (14 ± 1 psi). The pressure on the digital indicator at pressure tap (3) must be 0 kPa (0 psi).
Connect the wiring harness to the synchronizing solenoid.
Slowly increase the scraper engine to the HIGH IDLE rpm.
Note: The machine will try to move during this step.
The pressure on the gauge at pressure tap (4) should increase to 2070 ± 30 kPa (300 ± 4 psi).
Disconnect the wiring harness to the synchronizing solenoid (1).
The pressure on the gauge at pressure tap (4) should be no more than 910 kPa (132 psi).
When the test is complete, place the rotary selector spool in the NEUTRAL position. Turn on the parking brakes. Shut down the engines. Remove the test equipment from the machine.

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Illustration 3	g03632404
Lockup Clutch and Synchronizing Valve (5) Synchronizing valve (6) Spacers

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Table 3
Spacer Chart for the Modulation Relief Valve
Part Number	Thickness	Change in Pressure
5M-7914	0.25 mm (0.001 inch)	10.0 kPa (1.45 psi)
5M-7915	0.91 mm (0.036 inch)	35.0 kPa (5.08 psi)

If the pressure at pressure tap (4) in Step 4 is too low, the following problems may have occurred:

The setting of synchronizing valve (5) is too low. Add spacers (6) to change the pressure setting of the synchronizing valve. Refer to Table 3.
The valve spring may be weak or broken.

If the pressure at pressure tap (4) in Step 4 is too high, the following problems may have occurred:

The setting of synchronizing valve (5) is too high. Remove spacers (6) to change the pressure setting of the synchronizing valve. Refer to Table 3.
The valve spring may be weak or broken.

If the pressure at pressure tap (3) in Step 4 is not 0 kPa (0 psi), the following problems may have occurred: