Air Pressure Tests
AIR PRESSURE CHECKSNOTE: A no drive condition can exist, even with correct transmission fluid pressure, because of inoperative clutches or bands. On automatic transmissions, an erratic shift can be caused by a stuck governor valve. The inoperative units can be located through a series check by substituting air pressure for fluid pressure to determine the location of the malfunction.
1. When the selector lever is at 2, a no drive condition may be caused by an inoperative forward clutch.
2. A no drive condition at D may be caused by an inoperative forward clutch or one-way clutch.
3. When there is no drive in 1, the problem may be improper functioning of the forward clutch or simultaneous malfunction of the low reverse band and the one-way clutch.
4. No drive in R may be the result of a malfunctioning reverse high clutch or lo reverse band.
Fluid Passage Identification.:
5. To perform air pressure checks, loosen the oil pan bolts and lower one edge to drain the transmission, then remove the oil pan and valve body assembly. Inoperative bands and clutches can be located by introducing air into the specified transmission case passages.
Forward Clutch
1. Apply air pressure to the transmission case forward clutch passages.
2. A dull thud should be heard when the clutch piston is applied.
3. If no noise is heard, place the finger tips on the input shell and again apply air pressure to the forward or front clutch passage.
NOTE: Movement of the piston should be felt as the clutch is applied.
Governor
1. Apply air pressure to the forward clutch feed to governor passage and listen for a sharp whistling or clicking noise.
2. The noise indicates governor valve movement.
Overdrive Servo
1. Hold the air nozzle in the overdrive servo apply passage.
2. Operation of the servo is indicated by a tightening of the overdrive band around the overdrive drum.
3. Continue to apply air pressure to the servo apply pressure and introduce air pressure into the overdrive servo release passage.
4. The overdrive servo should stroke off, releasing the overdrive band.
Overdrive Clutch
1. Apply air pressure to the overdrive clutch feed passage.
2. A dull thud indicates that the overdrive clutch piston has moved to the applied position.
Reverse High Clutch
1. Apply air pressure to the reverse high clutch.
2. A dull thud indicates that the reverse high clutch piston has moved to the applied position.
3. If no noise is heard, place finger tips on the clutch drum and again apply air pressure to detect movement of the piston.
Intermediate Servo
1. Hold the air nozzle to the intermediate servo apply passages.
2. Operation of the servo is indicated by a tightening of the intermediate band around the drum.
3. Continue to apply air pressure to the servo apply passage and introduce air pressure into the intermediate servo release passage.
4. The intermediate servo should release the band against the apply pressure.
Low Reverse Servo
1. Apply air pressure to the low reverse servo.
2. The low reverse band should tighten around the drum if the servo is operating properly.
Air Pressure Check Diagnosis
1. If the servos do not operate, disassemble, clean, and inspect them to locate the source of the trouble.
2. If air pressure applied to either of the clutch passages fails to operate a clutch, or operates both clutches at once, remove and, with air pressure, check the fluid passages in the case and front pump to detect obstructions.