This TSB from GM addresses the diagnosis of cracked or broken transmission cases in 2006 and prior cars and light trucks, Hummer H2 and H3 and 2005-2006 Saab 9-7X vehicles equipped with 4L60/4L60-E/4L65-E or 4L80-E/4L85-E or Allison Series 1000 automatic transmissions.
A cracked or broken transmission case is most often the result of abnormal external torsional forces acting on the transmission case.
The following items should be considered. It is important to inspect the vehicle for signs of an out-of-line condition, impact damage or foreign material to the following components:
- The transmission
- The engine mounts
- The transmission rear mount and crossmember
- Vehicle frame damage that alters the front to rear alignment of the driveshaft
- Front and rear driveshafts
- Wheels (caked with mud, concrete, etc., and excessive balance weights)
- Tires (roundness, cupping)
- Transfer case (if 4WD)
A worn or damaged driveshaft U-joint has shown to be a frequent cause of transmission case cracking, especially on vehicles that see extended periods of highway driving.
For driveshaft damage or imbalance, inspect the driveshafts for dents, straightness/runout or signs of missing balance weights. Also, inspect for foreign material such as excessive undercoat on the driveshafts.
The driveshaft working angles may be excessive on non-canceling, especially if the vehicle carrying height has been altered (lifted or lowered) of if the frame has been extended or modified.
Inspect for damaged or worn upper or lower rear control arms or bushings.
Inspect for a rear axle that is not seated in the rear spring properly (for leaf spring vehicles).
Inspect for broken rear springs and/or worn leaf spring bushings.
