1990 - 2003 Corvette: Service Bulletin: Info - Diagnosis of Cracked or Broken Transmission Case

Number: 02-07-30-024
Subject: Info - Diagnosis of Cracked or Broken Transmission Case
Model Year:
1990-1993 Buick Roadmaster, Estate Wagon
1990-1996 Cadillac Fleetwood
1990-1996 Chevrolet Caprice
1990-2002 Chevrolet Camaro
1990-2003 Chevrolet Corvette
1995-1996 Chevrolet Impala
2000-2003 Chevrolet Impala
1990-1992 Oldsmobile Custom Cruiser Wagon
1990-2002 Pontiac Firebird
1990-2003 Chevrolet and GMC C/K Models (Silverado, Sierra, Avalanche, Suburban, Tahoe, Yukon, Yukon XL)
1990-2003 Chevrolet and GMC G-Van Models (Express, Savana)
1990-2003 Chevrolet and GMC M/L-Van Models (Astro, Safari)
1990-2003 Chevrolet and GMC S/T Models (S-10, Sonoma, Jimmy, Blazer, TrailBlazer)
2000-2003 Cadillac Escalade
1991-1994 Oldsmobile Bravada
1996-2002 Oldsmobile Bravada
with 4L60/4L60E/4L65E or 4L80E/4L85E or Allison® Series 1000 Automatic Transmission

Diagnosing the cause of a cracked or broken transmission case requires additional diagnosis and repair or a repeat failure will occur.

A cracked or broken transmission case is most often the result of abnormal external torsional forces acting on the transmission case. If none of the conditions listed below are apparent, an internal transmission component inspection may be required. Repairs of this type may be the result of external damage or abuse for which General Motors is not responsible. They are not the result of defects in materials or workmanship. If in doubt, contact your General Motors Service Representative.

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
The driveshafts (both front and rear)
The wheels (caked with mud, concrete, etc.)
The tires (roundness, lack of cupping, excessive balance weights)
The transfer case (if the vehicle is 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. Always inspect the U-joint condition when diagnosing this condition.
For driveshaft damage or imbalance, Inspect the driveshafts (both front and rear) for dents, straightness/runout or signs of missing balance weights. Also, inspect for foreign material such as undercoat sprayed on the driveshaft.
The driveshaft working angles may be excessive or non-canceling, especially if the vehicle carrying height has been altered (lifted or lowered) or if the frame has been extended or modified.
Damaged or worn upper or lower rear control arms or bushings.
A rear axle that is not seated in the rear spring properly (leaf spring vehicles).
Broken rear springs and or worn leaf spring bushings.

In some cases, the customer may not comment about a vibration but it is important to test drive the vehicle while using the electronic vibration analysis tool in an attempt to locate the cause of the torsional vibration. Refer to the Vibration Diagnosis and Correction sub-section of the appropriate Service Manual for more details on diagnosing and correcting vibrations.

GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.