SERPENTINE BELT CHIRP/SQUEAK OR PREMATURE WEAR (REPL. BELT). GMC Truck GMC Suburban

SUBJECT: SERPENTINE BELT CHIRP/SQUEAKING OR PREMATURE WEAR (DIAGNOSE/ REPLACE BELT)

MODELS: 1992-93 G VANS 1990-93 M/L VANS AND S/T, C/K TRUCKS

THIS BULLETIN IS BEING REVISED TO ADD 1990-93 MODEL YEAR C/K AND S/T TRUCKS WITH 4.3L (LB4, L35), 5.0L (L03), OR 5.7L (L05) ENGINES.

CONDITION:

--------- Some 1992-93 G-Vans with 4.3L (LB4), 5.0L (L03), 5.7L (L05), 1990-93 M/L Vans with 4.3L (LB4, L35, LU2), and 1990-93 C/K or SfT Trucks with 4.3L (LB4, L35), 5.0L (L03), or 5.7L (L05) engines may experience a chirping sound, a squeaking noise, or premature wear on the outer skin of the serpentine belt accessory drive.

CAUSE/CORRECTION: ---------------- The cause of the above conditions can be attributed to the following:

"SQUEAKING NOISE"

This condition typically occurs on vehicles equipped with air conditioning. The condition may be caused by a belt misalignment between the A/C compressor and the belt tensioner pulley. The belt misalignment causes the belt to rub against the front, rear, or inner edges of the A/C pulley grooves, creating a "squeaking" sound. For a multiple ribbed belt it is important that the grooves of the belt match the grooves in the pulleys. A mirror placed close to the pulley and belt may be helpful when inspecting the belt to pulley groove match. To verify alignment, place a straight edge or position a cord across 2 pulleys so they touch at all points. Turn each pulley one half revolution and recheck with the straight edge or cord. If contact is not made at all points check for a warped or bent shaft or, refer to the service manual (Section 6B-Engine Cooling) for proper inspection and adjustments.

**NOTE: Squeaking noise and chirping sounds should not be confused while diagnosing the concern. "Squeaking" is more of a sound which is continuous in nature. "Chirping" is of short duration intermittent, and a high pitched sound.

"CHIRPING SOUND"

The cause of the chirping sound may be the result of contamination or paint in the pulley grooves. If contamination or paint is noticed, remove the serpentine belt using procedures in section 6B, (Engine Cooling) of the service manual. Remove all contamination or paint from all pulley grooves. A wire brush mounted on an electric drill can be used to perform this operation. Caution should be taken when using the wire brush. After completion of the cleaning operation, inspect all locations. The surfaces should be smooth and free from burrs and rough edges. Do not over buff, this may result in an out of round condition on the pulley If the power steering pulley is suspect of causing the chirp sound, verify that the power steering pump pulley is aligned and flush to the power steering pump assembly, reference section 3B1 (Power Steering) and section 6B (Engine Coding) of the service manual for proper inspection and adjustments.

**NOTE: Belt dressing is NOT to be used on the serpentine belt. This will only aggravate the chirping condition.

"PREMATURE WEAR"

This condition will occur on vehicles with air conditioning only. The condition can be identified by scuffing or marring of the outer belt skin or the belt ribs where a possible interference may take place.

This condition may be attributed to belt interference between the water pump pulley and belt tensioner pulley (Figure 1). The belt tensioner pivots both directions from the center pivot axis which can result in the serpentine belt coming in contact with itself at the water pump pulley. To correct this condition, loosen the generator bracket bolts (3) and move the top of the bracket to its most outward position (Figure 1). This will move the tensioner pulley away from the water pump pulley increasing clearance, to eliminate contact. Tighten the generator bracket bolts after the bracket has been repositioned.

**NOTE: Some cleaning agents or mineral oils can attack the belt compound and should not be used in this location. This may be another contributor to premature wear.

If a new serpentine belt is required for the chirping sound or premature wear, new accessory drive serpentine belts have been released to GMSPO. The new belts will supersede the existing part numbers.

SERVICE PARTS INFORMATION:

Part Number Description Qty. ----------- ----------- ---- 10210382 Belt-Fan w/o C60, C69 1 10210383 Belt-Fan w C60, C69 1

S/T and C/K

An improved belt is available for use on 1990 through 1993 S/T and C/K trucks with L35, LB4, L03, or L05 engines equipped with C60 (air conditioning) but without K19 (A.I.R.). The new belt is less prone to "chirping." If, after performing standard diagnostic procedures, a serpentine belt replacement is required, use P/N 10189265.

NOTE: P/N 10189265 replaces P/N 10069211.

Parts are currently available from GMSPO.

WARRANTY INFORMATION:

For vehicles repaired under warranty for Noise use:

Labor Operation Labor Time ---------- ---------- T7460 0.2 hours Clean A/C pulley and inspect for proper alignment

0.2 hours Loosen and align P/S pump pulley (include R and R lower shroud)

Note: T7460 is coded to base vehicle coverage in the warranty system.

For vehicles repaired under warranty for replacing serpentine belt use:

Labor Operation Description Labor Time --------- ----------- ---------- J0667 Belt-Drive, Replace See Applicable Labor Time Guide

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.