REAR BRAKE HOWL / MOAN NOISE (REPLACE BRAKE DRUMS)

Subject: Rear Brake Howl/Moan Noise (Replace Brake Drums) ------------------------------------------------

Models: 1995 Chevrolet and GMC C/K 2500 Models with JB7/JD7 Brake Systems and 9.5" Rear Axles ------------------------------------------------

This bulletin is being revised to include drawings of C/K model rear axle covers so that dealer personnel can more easily identify trucks equipped with 9.5" axles. Please discard Corporate Bulletin Number 56-50-10 (Section 5 - Brakes).

Condition

A howl or moan noise emanating at the rear of the vehicle may be noticed under a moderate brake pedal application. The noise is most noticeable at low speeds near the end of a stopping maneuver.

Cause

Normal vibrations produced during braking may approach the resonant frequency of the brake drums.

Correction

The current 13 x 2.5" brake drums should be replaced with 13 x 3.5" brake drums (P/N 15960224). The larger brake drums have a different resonant frequency which should eliminate the moan/howl noise. Refer to Figure 1 to determine which axle is used in your customer's truck.

Service Procedure

Replace the brake drum as described in Section 4Bl of the 1995 C/K Service Manual.

Parts Information

P/N Description Quantity --- ----------- --------

15960224 13x3.5" Brake Drum 2

Parts are currently available from GMSPO.

Warranty Information

For vehicles repaired under warranty, use:

Labor Operation Description Labor Time ---------- ----------- ----------- Drum, Brake- Use Published H0207 Remove and Labor Operation Replace Time

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.