Air Pressure Tests

Air Pressure Tests

A NO DRIVE condition can exist, even with correct transaxle fluid pressure, because of inoperative clutches or bands. An erratic shift can be located through a series of checks by substituting air pressure for fluid pressure to determine the location of the malfunction.

When the shift control selector lever is in a forward gear range ( O/D, D, 2,1), a NO DRIVE condition may be caused by an inoperative forward clutch, overrunning or low/intermediate band. No manual low (1) coast could be caused by an inoperative direct clutch or direct overrunning clutch.

Failure to drive in R (REVERSE) could be caused by a malfunction of the reverse clutch, forward clutch or low/intermediate overrunning clutch.

Follow the procedure to determine the location of the inoperative clutch or band by introducing air pressure into the various test plate passages.
1. Drain transmission fluid and remove transmission oil pan.
2. Remove main control cover.
Then remove pump assembly and main control valve body.
3. Install air pressure test plate with chain cover gasket.






Note: Use only dry, regulated air 276 kPa (40 psi) maximum.

4. The inoperative clutches or bands can be located by introducing air pressure into the various test plate passages as follows:

Forward Clutch Cylinder
Apply air pressure to forward clutch test port. A dull thud can be heard, or movement of piston felt when clutch piston is applied. If clutch seal(s) is leaking, a hissing sound will be heard.

Intermediate Clutch Cylinder
Apply air pressure to intermediate clutch test port. A dull thud can be heard, or movement of intermediate clutch piston (7E005) can be felt on case, as intermediate clutch piston is applied. If clutch seal(s) is leaking, a hissing sound will be heard.

Direct Clutch Cylinder
Apply air pressure to direct clutch test port. A dull thud can be heard, or movement of clutch piston (7A262) felt on case as intermediate clutch piston is applied. If clutch seal(s) is leaking, a hissing sound will be heard.

Overdrive Servo
Apply air pressure to overdrive servo apply test port. Operation of servo is indicated by a tightening of overdrive band (7F 196) around overdrive drum. Because of the cushioning effect of the overdrive servo piston return spring (7F201), application of overdrive band may not be heard or felt. The servo should hold air pressure without leakage and a dull thud should be heard when air pressure is removed, allowing overdrive servo piston (7F200) to return to release position.

Low-Intermediate Servo
Apply air pressure at low-intermediate servo feed test port. The low-intermediate band should tighten around rear sun gear and drum (7A626). Because of the cushioning effect of the servo piston spring (7D028), application of low and intermediate band (7D034) may not be heard or felt.

The servo should hold air pressure without leakage and a dull thud should be heard when air pressure is removed, allowing servo band piston (7D022) to return to release position. Apply air pressure to low-intermediate servo release test port while continuing to pressurize the test port. Servo band piston should return to the release position. The servo band piston should loosen and a dull thud should be heard. Release the feed test port. The release test port should hold pressure without leakage. Any leakage or failure of servo band piston movement requires servo service.

1-2, 3-4 and "ND" Accumulators
Apply air pressure to each accumulator feed port. Accumulator should apply. Because of the cushioning effect of the accumulator release spring, application of accumulator may not be felt or heard. The accumulator should hold air pressure without leakage and a dull thud should be heard when air pressure is removed, allowing accumulator to return to release position.

Front Lube, Rear Lube and Differential Lube
Apply air pressure to front lube, rear lube and differential lube test ports. These passages can only be checked for blockage. If either passage holds air pressure, remove service tool plate and check for an obstruction or damage.

Test Results
If the servos do not operate, disassemble, clean and inspect them to locate the source of the trouble.

If air pressure applied to the clutch passages fails to operate a clutch, or operates clutches simultaneously, remove and with air pressure, check the fluid passages in the chain cover (7G188), driven sprocket support and clutches to detect obstructions.

If air pressure applied to the accumulator passages fails to operate an accumulator, remove, and with air pressure, check the fluid passages in the chain cover to detect obstructions.