VIBRATION ON ACCELERATION PROCEDURE TO PROVIDE CLEARANCE

MODELS: 1988 S/T WITH 4.3L (VIN CODE Z)

THIS BULLETIN IS BEING REVISED TO INDICATE REVISED TORQUE SPECIFICATION AND ADDITIONAL DIAGNOSTIC INFORMATION AND CANCELS GMC TRUCK BULLETIN 88-T-123 DATED JUNE, 1988, ALL COPIES OF WHICH SHOULD BE DESTROYED.

Some 1988 S/T trucks equipped with 4.3L engines may experience a vibration that can be felt in the floor pan area near the shifter, in the right hand passenger seat foot area, or on the steering column. These conditions may be caused by the following items:

1. The shifter rod that goes from the steering column to the transmission equalizer lever (#340 and #338 in Figure 36 page 7A-45 of the 1988 S/T Manual) hitting the exhaust crossover pipe and/or the equalizer lever making firm contact at the shift lever (T-truck only).

2. The exhaust pipe to catalytic converter clamp (Figure 7, page 6F-6 of the 1988 S/T Manual) hitting the catalytic converter heat shield.

3. The exhaust pipe to converter installation allows the exhaust pipe to contact the transmission crossmember.

To repair these conditions, use the following procedures:

To repair condition 1:

A. Raise vehide on hoist.

B. Check transmission linkage for correct adjustment.

C. Check exhaust pipe for shifter rod interference (shiny spot on pipe).

D. If linkage hits pipe, remove 15mm (5/8 in) from bottom of rod.

E. Put transmission into low gear and mark exhaust pipe area near linkage.

F. Put transmission in park. Using a hammer lightly dimple exhaust pipe for additional clearance. Dimple should be no larger than 3/4" in diameter and 1/8" deep.

G. (T-truck only) Check equalizer lever for firm contact at the shift lever inboard side of the guide slot. (See Figure No. 1)

H. If firm contact is evident, add an additional washer (#10 in Figure #1) P/N 14074908 to adjust equalizer lever outboard toward the center of tbe guide slot to eliminate contact.

To repair condition 2:

A. Raise vehicle on hoist.

B. Note location of clamp rotation on pipe. Some clamps are located with the lower lock ring (nuts) pointed towards the transmission. If the clamp is located in such a manner, loosen clamp and rotate it down so the nuts point toward the ground and retighten to 58Nm (43 ft/lbs.)

To repair condition 3:

A. Loosen converter clamp until it will rotate around the pipe. Using a suitable pry bar, move exhaust system rearward to correctly locate exhaust system 5/8" in back of the transmission crossmember and re-torque nuts to 58 Nm (43 ft/lbs. )

For repairs performed under warranty, use the following labor operations and times:

Labor Op Labor Time -------- ---------- Shift Linkage (shorten) K5244 .3 Hr Exhaust/muffler clamp L2020 .3 Hr Exhaust system align L2004 .3 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.