Hydraulic Pressure Tests
OVERVIEWPressure testing is a very important step in the diagnostic procedure. These tests usually reveal the cause of most transaxle problems.
Before performing pressure tests, check fluid level and condition, as well as control cable adjustments. Fluid must be at operating temperature (150 to 200 degrees F).
Install an engine tachometer. Raise vehicle on a hoist that allows front wheels to turn, and position tachometer so it can be read.
Disconnect throttle cable and shift cable from transaxle levers so they can be controlled from outside the vehicle.
Attach 150 psi gauges to ports required for test being conducted. A 300 psi gauge (C-3293) is required for reverse pressure test at rear servo.
Fig. 3:
Test port locations are shown in (Fig. 3).
TEST ONE (SELECTOR IN 1)
1. Attach gauges to line and low-reverse ports.
2. Operate engine at 1000 rpm for test.
3. Move selector lever on transaxle all the way rearward (1 position).
4. Read pressures on both gauges as throttle lever on transaxle is moved from full clockwise position to full counterclockwise position.
Elements In Use At Each Position Of The Selector Lever:
Fig. 4:
5. Line pressure should read 52 to 58 psi with throttle lever clockwise. Pressure should gradually increase to 80 to 88 psi as lever is moved counterclockwise.
6. Low/reverse pressure should read the same as line pressure, within 3 psi.
7. This tests pump output, pressure regulation, and condition of rear clutch and rear servo hydraulic circuits.
TEST TWO (SELECTOR IN 2)
1. Attach one gauge to line pressure port, and tee another gauge into lower cooler line fitting. This will allow lubrication pressure readings to be taken..
2. Operate engine at 1000 rpm for test.
3. Move selector lever on transaxle one detent forward from full rearward position. This is selector 2 position.
4. Read pressures on both gauges as throttle lever on transaxle is moved from full clockwise position to full counterclockwise position.
5. Line pressure should read 52 to 58 psi with throttle lever clockwise. Pressure should gradually increase to 80 to 88 psi. as lever is moved counterclockwise.
6. Lubrication pressure should be 10 to 25 psi with lever clockwise and 10 to 35 psi with lever at full counterclockwise.
7. This tests pump output, pressure regulation, and condition of rear clutch and lubrication hydraulic circuits.
TEST THREE (SELECTOR IN D)
1. Attach gauges to line and kickdown release ports.
2. Operate engine at 1600 rpm for test.
3. Move selector lever on transaxle two detents forward from full rearward position. This is selector D position.
4. Read pressures on both gauges as throttle lever on transaxle is moved from full clockwise to the full counterclockwise position.
5. Line pressure should read 52 to 58 psi with throttle lever clockwise. Pressure should gradually increase to 80 to 88 psi. as lever is moved counterclockwise.
6. Kickdown release is pressurized only in direct drive and should be same as line pressure within 3 psi, up to kickdown point.
7. This tests pump output, pressure regulation, and condition of rear clutch, front clutch, and hydraulic circuits.
TEST FOUR (SELECTOR IN REVERSE)
1. Attach 300 psi gauge to low-reverse port.
2. Operate engine at 1600 rpm for test.
3. Move selector lever on transaxle four detents forward from full rearward position. This is selector R position.
4. Low/reverse pressure should read 180 to 220 psi with throttle lever clockwise. Pressure should gradually increase to 260 to 300 psi. as lever is moved counterclockwise.
5. This tests pump output, pressure regulation, and condition of front clutch and rear servo hydraulic circuits.
6. Move selector lever on transaxle to D position to check that low/reverse pressure drops to zero.
7. This tests for leakage into rear servo, due to case porosity, which can cause reverse band burn out.
TEST RESULT INDICATIONS
1. If proper line pressure, minimum to maximum, is found in any one test, the pump and pressure regulator are working properly.
2. Low pressure in D, 1, and 2 but correct pressure in R, indicates rear clutch circuit leakage.
3. Low pressure in D and R, but correct pressure in 1 indicates front clutch circuit leakage.
4. Low pressure in R and 1, but correct pressure in 2 indicates rear servo circuit leakage.
5. Low line pressure in all positions indicates a defective pump, a clogged filter, or a stuck pressure regulator valve.
GOVERNOR PRESSURE
Test only if transaxle shifts at wrong vehicle speeds when throttle cable is correctly adjusted.
1. Connect a 0 - 150 psi pressure gauge to governor pressure take-off point. It is located at lower right side of case, below differential cover.
2. Operate transaxle in third gear to read pressures. The governor pressure should respond smoothly to changes in mph and should return to 0 to 3 psi when vehicle is stopped. High pressure (above 3 psi) at standstill will prevent the transaxle &from downshifting.
THROTTLE PRESSURE
No gauge port is provided for throttle pressure. Incorrect throttle pressure should be suspected if part throttle upshift speeds are either delayed or occur too early in relation to vehicle speed. Engine runaway on shifts can also be an indicator of low throttle pressure setting, or misadjusted throttle cable.
In no case should throttle pressure be adjusted until the transaxle throttle cable adjustment has been verified to be correct.