NEW EXHAUST KIT RELEASED (CONVERTER AND HEAT SHIELDS)

SUBJECT: KNOCK NOISE CAUSED BY EXHAUST PIPE CONTACT WITH UNDERBODY SHIELD AFTER WATER SLUSH

MODELS AFFECTED: 1985-1992 DE VILLES AND FLEETWOODS

This bulletin cancels and replaces Service bulletin T-90-88 which should be discarded.

Some 1985-1992 DeVilles and Fleetwoods may experience a knocking or banging noise from the underside of the vehicle when it is driven through water or slush. This condition may be caused by exhaust system ground out. This condition occurs when water from the road surface rapidly cools the lower half of the exhaust pipe. This causes the pipe to bend upward touching the heat shields just behind the catalytic converter outlet tube to intermediate pipe weld joint.

1991-1992 Models:

A new service kit, P/N 12353337 (Coupe) or 12353338 (Sedan), has been released for service. This kit contains a catalytic converter heat shield and intermediate pipe heat shield. A package of rivets is also included.

NOTE: When installing the shields, it is important that the shield be held securely against the underbody when the rivets are installed. Failure to do so may result in a rattle condition.

1985-1990 Models:

When using these shields on pre-1991 vehicles, it may be necessary to modify the shields to provide clearance for the underbody bracket. Modify the catalytic converter heat shield as follows:

1. Cut the shield a minimum of 10mm from the top edge of the attachment slot forward at a right angle to a line formed by four small dimples in the shield (approximately 30mm) on both the right-and-left-hand sides. Make a smooth curve at the corners and out along the line formed by the dimples removing a U-shaped piece of metal.

2. Bend the new edge to form a flange (5mm) all the way around.

Modify the exhaust muffler front heat shield assembly as follows:

1. Cut the shield a minimum of 10mm from the top edge of the attachment slot rearward at a right angle to a line formed by four small dimples in the shield (approximately 70mm) on both the right-and-left-hand sides. Make a smooth curve at the corners and cut along the line formed by the dimples removing a U-shaped piece of metal. Then bend the new edge to form a flange (5mm) all the way around.

NOTE: When using the shields on vehicles that have shorter attaching tabs that are screwed to standoffs, it may be necessary to drill off the standoffs. Position, locate, and drill a 13/64 inch diameter hole through the floor pan. The shields can then be attached using the rivets in the kit.

Parts are currently available from GMSPO.

For warranty purposes use Labor Operation L2400 at .3 hour.

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.