Air Pressure Tests

Air Pressure Tests

A no drive condition can exist, even with correct transmission 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 transmission range selector lever is in a forward gear range (D, 2, 1), a no drive condition may be caused by an inoperative forward clutch, or an overrunning one-way clutch.

Failure to drive in R (REVERSE) could be caused by a malfunctioning reverse clutch, reverse servo, or band. Follow the procedure to determine the location of the inoperative clutch or band by introducing air pressure into the various test plate passages.

Test Procedures

NOTE: Cover vent in test plate with a clean, lint-free shop towel to prevent spray when air is applied. Plugging vent hole during testing will result in inaccurate results.

NOTE: Use only dry regulated air pressure 276kPa (40 psi) max. A dull thud should be heard when the clutch or band applies. There should be no hissing sound when band or clutch applies.

Air Test Plate:

1. Drain transmission fluid and remove transmission oil pan.

2. Remove filter and seal assembly and main control valve body.

3. Install 4R44E/4R55E Transmission Test Plate T95L-7700-AH and Transmission Test Plate Gasket (T95L-7006-A).

CAUTION: Do not apply air to test the vent.

4. Apply air pressure to appropriate clutch port (refer to diagram). A dull thud may be heard or movement felt when clutch is applied or released. If clutch seals or check balls are leaking a hissing sound may be heard.

Test Results

If test results find that the servos do not operate, disassemble, clean and inspect them to locate the source of the concern.

If air pressure applied to the clutch passages fails to operate a clutch, or operates another clutch simultaneously, disassemble and use air pressure to check the fluid passages in the center support and clutches to detect obstructions.