CLUTCH DRIVEN PLATES CRACK (NEW PART NUMBERS RELEASED)
SUBJECT: CLUTCH DRIVEN PLATE CRACKS
MODELS: 1987-88 C6, C7, B6, 57L WITH 5.7L (VIN CODE A) OR 6.0L (VIN CODE B) GAS ENGINE WITH MANUAL TRANSMISSION
Some 1987-88 medium duty trucks equipped with 5.7L or 6.0L engines and manual transmission may experience repeated clutch disc cracks. This condition may be the result of improperly manufactured engine clutch housing. In the event a clutch disc cracks, the transmission to engine alignment must be checked prior to replacing clutch.
This condition should not be confused with normal clutch wear out or clutch abuse. Listed below is the inspection procedure to determine if the clutch housing is in proper alignment with the transmission.
SERVICE PROCEDURES
Refer to Service Manual, Section 7B, for removal and installation of manual transmission.
Runout Measuring Procedure:
The runout measurements are taken with a dial indicator equipped with a flat or sharp point which defines total runout in thousandths of an inch.
IMPORTANT: The dial indicator is a delicate, precision instrument and should be handled accordingly. It should be used with a magnetic base to eliminate movement of the gauge when measuring runout.
Measurement Procedure:
A. Clutch housing bore (pilot) runout (Figure 1).
1. Mount holding fixture on the rear of the crankshaft.
IMPORTANT: May be necessary to remove clutch fork.
2. Position dial indicator so it contacts the inside of the clutch housing where it fits onto the transmission.
3. Turn the engine over by hand. DO NOT USE ENGINE STARTER.
4. Measure total indicated runout. Maximum total indicated runout is .020 for SAE No. 1 and 2 housings.
B. Engine clutch housing face runout (Figure 2).
1. Mount holding fixture on the rear of the crankshaft.
IMPORTANT: May be necessary to remove clutch fork.
2. Position dial indicator so it contacts the face of the clutch housing.
3. Turn engine over by hand. DO NOT USE THE ENGINE STARTER.
4. Measure total indicated runout. Maximum total indicated runout is .010 for SAE No. 1 and 2 housings.
IMPORTANT: The total runout is the sum of the highest plus and minus reading. See Figure 1.
Repair Procedure
Replace the clutch housing if total runout exceeds maximum runout on either of the above measurements.
IMPORTANT: Service parts can be identified by purple dot painted on clutch housing. If purple dot is not found on clutch housing, follow procedures A and B after installation.
Manufacturing processing changes were made on June 15, 1988 to eliminate the potential for these conditions. Vehicle manufacturing breakpoints are listed below:
Chevrolet: 1GBG7D1B1JV119038 GMC: 1GDG6D1B0JV535835
Use applicable Labor Time and Operation numbers for removing and replacing clutch assembly. For measuring clutch housing, use:
Labor Operation - T7675 Labor Time -.4 Hr.
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.
