Service Information Regarding Rear Brake Drum Wheel Cylinder Inspections

This bulletin is being revised add model years and include all GM vehicles. Please discard Corporate Bulletin Number 03-05-24-001 (Section 03 - Suspension).

This bulletin provides information on proper inspection of rear drum brake wheel cylinders.

Important: It is not recommended that dust boots be removed during inspection processes as dirt and debris could contaminate the wheel cylinder bore causing premature wear of the wheel cylinder. In addition, most bores should look damp and some lubricant may drip out from under the boot as a result of lubricant being present.

All rear drum brake wheel cylinders are assembled with a lubricant to aid in assembly, provide an anti-corrosion coating to the cylinder bore, and lubricate internal rubber components. As a result of this lubrication process, it is not uncommon for some amount of lubricant to accumulate at the ends of the cylinder under the dust boot.

Over time, the lubricant may work its way to the outside of the boot and cause an area of the boot to look damp. Evidence of a damp area on the boot does not indicate a leak in the cylinder. However, if there is excessive wetness (i.e. drips) coming from the boot area of the wheel cylinder, it could indicate a brake hydraulic fluid leak requiring wheel cylinder replacement. (Refer to the Wheel Cylinder Replacement procedures in the appropriate Service Manual.)