MOMENTARY REAR TIRE 'CHIRP' (REPL. REAR WHEEL CYLINDERS)
SUBJECT: MOMENTARY REAR TIRE "CHIRP" (REPLACE REAR WHEEL CYLINDERS)
VEHICLES AFFECTED: 1988-93 C/K 25 PICKUPS JB7/JD7 AND 93 25 SUBURBANS W/L05 ENG
THIS BULLETIN SUPERSEDES AND REPLACES CORPORATE BULLETIN REFERENCE NUMBER 365005r.** THIS BULLETIN IS BEING REVISED TO CHANGE THE CANADIAN BULLETIN NUMBER FROM 93-5-120 TO 93-5-136.
CONDITION:
--------- Some owners of 1988-93 C/K 2500 pickups with JB7/JD7 brake systems or owners of some 1993 2500 4-wheel drive Suburbans with L05 engines may comment about a "No Load" condition which can cause their vehicle to exhibit a momentary rear tire chirp. This condition does not indicate improper functioning of the rear wheel antilock system and will not affect the vehicle's directional stability during a stop.
CAUSE:
----- C/K 2500 Series trucks are designed to carry loads and, therefore, they are equipped with brakes that are capable of good stopping performance under fully-loaded conditions. When these vehicles are braked to the point of wheel slide in a lightly-loaded condition, it is normal for the rear wheels to slide first. The design is consistent with industry practice and sound engineering principles that General Motors and other light-truck manufacturers have applied successfully for many years.
CORRECTION:
---------- NOTE: Some customers who operate their trucks under lightly loaded conditions most of the time may prefer less rear braking. If so, the following procedure is an acceptable method of reducing rear braking on the above models. However, the customer should be informed that there will be a reduction in brake performance when the truck is loaded, in that minimum stopping distances may be increased. This modification has been tested by General Motors and meets all the requirements of the Federal Standard for hydraulic service brakes FMVSS 105.
Check for abnormal vehicle loading conditions allowing for a large increase in weight distribution to the front end. Any abnormal condition should be resolved. Inspect the rear brake components for any contamination which may result in an "aggressive" condition.
If the vehicle is primarily operated under "no load" conditions and the driver comments on aggressive rear brakes, replace the 27mm ( 1-1/16 in.) rear wheel cylinders with 25.4mm ( 1 in.) cylinders as described in the procedure below.
SERVICE PROCEDURE:
1. Raise the vehicle and support with safety stands.
2. Remove the brake linings (refer to Section 5 in the appropriate Service Manual).
3. Remove the brake pipe.
4. Remove the bolts securing the wheel cylinder to the backing plate.
5. Remove the wheel cylinder.
6. Install the 1 in. wheel cylinder (P/N 18014081).
7. Install the bolts securing the wheel cylinder to the backing plate. Torque the bolts to 20 N.m (15 lbs. ft.).
8. Install the brake pipe.
9. Install the linings (refer to Section 5 in the appropriate service manual).
10. Repeat this procedure for the opposite rear wheel.
11. Bleed the brake system (refer to Section 5 in the appropriate service manual).
SERVICE PARTS INFORMATION
P/N Description Quantity --- ----------- -------- 18014081 25.4mm ( 1" Cylinder) 2
WARRANTY INFORMATION
For vehicles repaired under warranty use:
Labour Operation Description Labour Time ---------------- ----------- ----------- H0377 Remove and Replace 1.5 BOTH Wheel Cylinders
To allow additional time for cleaning parts on vehicles over 48,000 KM (30,000 miles,) 1.7
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.
