CONVERTIBLE SHAKE/JITTER (PROCEDURE TO IMPROVE)

SUBJECT: CONVERTIBLE SHAKE AND/OR JITTER

MODELS AFFECTED: 1990-91 REATTA CONVERTIBLE

THIS BULLETIN IS BEING REVISED TO CHANGE SERVICE PROCEDURE. PLEASE DISCARD BUICK BULLETIN NO. 91-10-26.

Some shake/jitter is a normal condition under certain road and/or climate conditions. Efforts to completely eliminate shake/jitter are often futile. However; some shake/jitter may be improved.

There are two basic types of shake associated with the Reatta convertible. First, a shake on rough roads, or when driving over railroad tracks, which dampens out after initial impact and should be considered a normal characteristic. No attempt should be made to try to repair this condition. The second shake or jitter, a constant shake between 50-65 mph, (similar to tire imbalance), on smooth roads at ambient temperatures above 70- F, can be addressed on 1990-91 convertibles. Use the procedure outlined below to improve 50-65 mph constant shake.

SERVICE PROCEDURE

1. Road test vehicle (with owner, if possible), to determine if the shake/ jitter is as described in the second part of paragraph two (2) of this bulletin.

2. Check and rebalance all four wheel and tire assemblies as described in Section 3E of the 1991 Service Information Manual.

3. Road test the car on a smooth road at 50-65 mph. If the shake is still objectionable, continue to Step 4 (1990 vehicles) or Step 5 (1991 vehicles).

NOTE: If tire non-uniformity is suspected even after balancing, temporarily install OEM assemblies from another Reatta vehicle and reevaluate to confirm shake condition.

4. Adjust the rear standing height (1990 vehicles only) by adding a 10mm shim, P/N 1648853, under the rear spring trim height adjustable shim. The 10mm shim should be installed under the 5mm shim. If this is done, the tab does not have to be removed and the shim will nest properly. If the 10mm shim is installed on top of the 5mm shim, trim the location tab off the bottom of the 10mm shim before installation. Refer to Figure 1.

5. Check and realign the front and rear suspension as described in Section 3A.

6. Replace upper cradle mounts (1990 vehicles only) at all six locations with the following part number:

Upper Insulator Assembly 03533046 six per vehicle

NOTE: Reuse cradle spacer, P/N 1626368, and bolt, P/N 1626873, with the above parts as received on the vehicle.

Follow procedures as outlined in Section 10-3 of the 1990 Service Information Manual.

7. Road test to ensure repair procedure has not induced any squeaks or rattles.

NOTE: 1990 Reatta convertible service parts list is as follows:

Insulator Assembly 03533046 (6) Spacer-Rear Spring 01648853 (2)

Parts are currently available from GMSPO.

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.