For 1990-2009 cars

# SERPENTINE DRIVE BELT SERVICE INFORMATION

HT4100 SERPENTINE DRIVE BELT SERVICE

#### VEHICLES AFFECTED: 1985-87 DE VILLE AND FLEETWOOD, ------------------ 1986-87 ELDORADO AND SEVILLE, AND 1987 ALLANTE

Introduction of the serpentine belt accessory drive system on transverse HT4100 engines has presented service technicians with a unique new technology to become familiar with. This bulletin will clarify and define current service issues. This bulletin supplements information previously published in bulletin 87-641-114.

#### BELT APPLICATIONS

There are currently two serpentine drive belts available from General Motors Service Parts.

1. Belt 1625691. This belt is 2200mm long and is used on 1985 FWD C-cars before VIN 321327 (108 amp generator - 52mm black generator pulley). This belt should not be used on later vehicles with the 120 amp generator.

2. Belt 1643049. This belt is 2210mm long and is used on 1985 FWD C-cars after VIN 321327 (120 amp generator - 57mm yellow generator pulley), as well as all 1986-1987 C, E, K, and V cars. Likewise, this belt should not be used on early 1985 cars with the 108 amp generator. This belt replaced 1625690 as described in bulletin 87-641-114.

#### BELT WEAR

Figures 1 through 4 illustrate various stages of belt wear to aid technicians in belt replacement decisions. Condition of the belt ribs is best judged as the belt is bent back over the water pump pulley as shown.

A serpentine belt will stretch over its service life much like a V belt will do. However, unlike V belts, the serpentine drive system incorporates an automatic tensioner/adjuster to absorb belt growth and provide constant belt tension throughout the belt's service life. The belt must be replaced when the tensioner reaches the limit of its travel. Replacement is required when the arrow cast into the tensioner reaches the end of the "operating range" indicator stamped into the tensioner bracket, Figure 5.

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.