A/T - Harsh Forward Engagement
DATE: 1996TECHNICAL BULLETIN # 339
TRANSMISSION: 3T40
SUBJECT: Harsh forward engagement
APPLICATION: GM
3T40
Harsh Forward Engagement
A harsh forward engagement condition is often caused by high line pressure or incorrect clutch stack up. Line pressure in drive (at an idle) should be 55-75 psi. If line pressure is normal, the transmission will need to be removed.
One of the most common errors in clutch drum assembly is incorrect clearance. It is important that the forward clutch have less clearance than the direct. This will ensure that when the transmission is not in gear, the geartrain will remain stationary. If the direct clutch is too tight and forward clutch too loose, the geartrain can rotate when the transmission is not in gear. This will cause an aggressive engagement as the forward clutch applies and the geartrain comes to a stop.
Proper clearance for the forward clutch is 025"-.035". Proper clearance for the direct clutch is .040"-.070". Also, on 1980-85 units, forward engagement can be further enhanced by adding a second wave plate as shown in the illustration. 1986 and later units already have this.
NOTE:
This information excludes external components such as worn drive-axles, and internal components such as loose end play or worn out geartrain components which may also cause this condition.