A/T - ZF4HP22 Burning A (Foward) Clutch
DATE: Jan 1990TRANSMISSION: ZF4HP22
BULLETIN: # 9001004
SUBJECT: Burning "A" clutch
ZF4HP22 "A" CLUTCH FAILURE
Burning "A" Clutch
A common problem with the ZF4HP22 is the burning of the "A" or forward clutch. Figure 1. One possible cause is excessive clearance between the "A" clutch support bushing and the stator support shaft. Figure 2.
The bushing in the "A" clutch not only supports the drum but it also seals the feed oil to the clutch. The feed oil must be contained at three areas for proper clutch application. These areas are the metal sealing ring and the rubber O-ring on the input shaft (figure 3) and the bushing in the "A" clutch drum. If the bushing has excessive wear (which may not be visible to the eye) it will leak just like a broken or missing sealing ring.
Keep in mind, if the bushing to support clearance is .007" it will leak as much oil as a .134" hole. (a little more than 1/8") That is quite a leak, and will result in clutch failure.
The outside diameter of the support should not be less than 1.260". The bushing should not measure less than 1.263" inside diameter. This will give .003" bushing to support clearance which will work and should be considered maximum clearance for this application.
BULLETIN RECAP
^ Measure the support
^ Replace the support if it measures less then 1.260"
^ Measure the bushing to support clearance.
^ Replace the "A" clutch drum if the clearance exceeds .003"
FOR ADDITIONAL INFORMATION: ATRA Bulletin TSB 88-43