A/T - Shudder or Vibration During Coastdown 4-3 Shift
TSB 85-9SUBJECT: AOD
COMPLAINT:
During a coastdown a 4-3 shift, shudder or engine torsionals can be felt. May be severe enough to cause the vehicle to shake.
CAUSE:
The cause may be the too-low speed at which the 4-3 shift is occurring.
CORRECTION:
If the problem occurs after a rebuild and no other complaint is present, do the following:
1) Remove governor, clean and inspect. The valves have been wearing into the body, causing erratic shifting. Replace if needed.
2) File case face smooth and use double gaskets between case and separator plate. You may also wish to strip the valve body and block sand with fine emery paper.
3) If everything is OK to this point, then install a heavier spring for the 3-4 shift valve. This spring should be only slightly heavier to raise the shift point about 3 mph.
Note that the 3-4 shift will be slightly later, but this should be considered normal with this modification.