MOAN/VIBRATION 45-55 MPH MATCH MOUNT PROPELLER SHAFT

SUBJECT: MOAN/VIBRATION 75-90 KPH (45-55 MPH) - (MATCH MOUNT PROPELLER SHAFT, ALIGN EXHAUST SYSTEM, INSTALL BRACE)

VEHICLES AFFECTED: 1992 BUICK ROADMASTER SEDAN WITH 5.7L ENGINE (VIN CODE 7)

Some 1992 Buick Roadmaster sedans with 2.56 ratio rear axles (RPO GM8), and assembled prior to VIN breakpoint NR464131, may exhibit a slight vibration/moan condition. This condition is most apparent during light acceleration from 75-90 kph (45-55 mph) on a grade, with transmission in 4th gear and torque converter clutch (TCC) applied.

CAUSE:

------ This vibration/moan condition may be attributable to one or more of the following causes that may excite vehicle underbody.

Cause 1: Incorrect match mounting of propeller shaft to rear axle assembly.

Cause 2: Misalignment of exhaust system.

Cause 3: Frame rail vibration at rear of vehicle.

CORRECTION:

----------- To insure correction of complaint vehicles, all of the following three corrective action steps must be performed:

Correction 1: Inspect and correct, as required, the match mounting of propeller shaft to rear axle assembly following procedure shown on Figure 1.

Correction 2: Align exhaust system following procedure shown on Figure 2.

Correction 3: Install new frame brace, P/N 10225142, to rear frame rails, at lower energy absorber attachments following procedure shown on Figure 3.

For vehicles repaired under warranty use:

Labor Time: 0.6 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.