ENGINE VIBRATION OR SHUDDER AT 800 RPM

MODELS AFFECTED: 1986-1989 BROUGHAMS

Some Cadillac Broughams equipped with a 5.0L engine and 200 4R transmission may exhibit an engine vibration or shudder condition at off idle engine speeds of approximately 800 rpm due to an improperly piloted transmission torque converter. This condition might also feel like an erratic engine miss.

Improper piloting of the torque converter to the engine crankshaft may occur due to improper assembly, metal burrs on either the torque converter hub or crankshaft pilot hole, or due to excess grease in the crankshaft pilot hole.

When diagnosing this condition:

1. Remove the bolts that retain the torque converter to the engine flexplate (flywheel).

2. Move the torque converter fully rearward away from the engine.

3. Run the engine to determine if the condition is eliminated.

If the condition is gone, torque converter imbalance or improper piloting may be indicated. Inspect the torque converter for damage or missing balance weights. If the torque converter is damaged or balance weights are missing, replace the torque converter.

If no damage or missing weights are noted, reposition the torque converter back into its proper installed position. Due to part tolerances, it may be necessary to use two small pry bars between the transmission case and the torque converter to lightly lift and "walk" the torque converter into place.

The engine flexplate should contact the torque converter evenly at all three bolt lug positions. If the flexplate does not make even contact with all three lugs, then the flexplate is bent as a result of improper piloting and should be replaced. If the torque converter cannot move forward enough to contact the flexplate, there may be metal burrs or excess grease present in the crankshaft pilot hole. It will be necessary to remove the transmission to perform the appropriate repair. If the torque converter installs properly and no evidence of a bent or damaged flexplate exists, an out of balance torque converter may be present. Diagnose as follows:

1. Change position of converter to flexplate 120 DEG at a time to cancel out engine and converter unbalance. Recheck in each position for vibration improvements.

2. If the vibration condition still exists, leave the torque converter/flexplate in the best balanced position. Install a longer torque converter to flexplate bolt with washers as needed in each position, one at a time, until the best balance is achieved.

IMPORTANT: Be sure the bolts are not bottoming in the holes. Always rotate the converter by hand after adding washers to ensure proper clearance.

3. If the vibration condition still exists, replace the torque converter.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those 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 a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.