Hydraulic Pressure Testing

Pressure testing can reveal the cause (not the symptom) of most transaxle problems. Hydraulic pressure testing verifies the proper functioning, or malfunctioning, of the following hydraulic components:
^ Oil pump
^ Regulator valve
^ Hydraulic circuits

Transaxle problems can be isolated to an electronic or hydraulic/mechanical component. The hydraulic pressure test is a helpful tool in determining whether the problem is electronic or hydraulic/ mechanical.

Though reference must be made to the appropriate procedure for testing purposes, sequence, pressure tap reading and test results, there are some general guidelines that apply to this procedure, as follows:
^ Verify proper fluid level and condition.
^ Verify and correct for proper gearshift linkage adjustment.
^ Verify that electrical connectors associated with the transaxle are properly connected and are clean and secure.
^ Allow the transaxle to reach operating temperature before testing. Any of the above conditions, if not checked and/or corrected, can result in false readings and inaccuracies.

AIR LEAK TESTING
There are two types of air pressure testing that can be performed on the transaxle:
^ Air pressure testing the clutches
^ Air pressure testing the transaxle sump

Both procedures can be performed with the transaxle in the vehicle. Clutch air pressure testing can aid in diagnosis and can verify clutch operation or non-operation when used in addition to hydraulic pressure testing. For example, a vehicle with a "no drive" condition, hydraulic pressure testing can indicate that the fluid pressure is correct but cannot detect if the clutch piston is able to move. Air pressure testing can be used to determine if the piston physically moves.

NOTE: AIR TESTING THE CLUTCHES CAN BE ACCOMPLISHED IN THE VEHICLE. HOWEVER, REMOVAL OF THE VALVE BODY IS NECESSARY. SPECIAL ADAPTER PLATES ARE ALSO REQUIRED AND ARE INSTALLED IN PLACE OF THE REMOVED VALVE BODY.

The following lists general guidelines to be followed for conducting an air pressure leak test:
1 Use clean, dry air regulated to no more than 30 psi.
2 Remove the valve body and install the special adapter plates.
3 Apply air pressure to the indicated ports, one at a time, while listening and watching for clutch operation.

If the clutch is physically operating, a dull thud will be heard and movement will be seen when viewing the designated area. If the clutch piston seals are leaking, a large amount of air will be heard and any residual fluid may be leaking.

Air testing the sump is only an aid and is not the end-all for locating difficult leaks. Some leaks may not show up until the transaxle is a operating temperature. Areas to check for leaks are as follows:
^ The entire transaxle case for porosity
^ Gasket areas where case components (covers) are bolted together
^ Seal or 0-ring areas where shafts protrude from the case
^ Bolt hole areas
^ Drain plugs
^ Fittings