A/T - Vibration/Drone Noise With TCC Applied

File In Section: 7 - Transmission

Bulletin No.: 67-71-44A

Date: June, 1996

Subject:
Vibration/Drone Noise between 1700-1900 RPM with TCC Locked
(Replace the EPROM)

Models:
1993-95 Chevrolet and GMC G Vans
with a 6.2L or 6.5L Diesel Engine (VINs J, Y - RPOs LL4, L57) and
HYDRA-MATIC 4L80-E Automatic Transmission (RPO MT1)

Transmission Models:
3KDP, 3KFP, 3PAP 3PBP, 4HAP, 4HCP, 4LAP, 4LBP, 5ALP, SLAP

This bulletin is being revised to update the new scan i.d. numbers in the parts information chart. Please discard Corporate Bulletin Number 67-71-44
(Section 7 - Transmission).

Condition

A driveline vibration or drone type noise is heard throughout the vehicle when the engine is between 1700-1900 RPM with the Torque Converter Clutch (TCC) applied.

Cause

Engine firing pulses are transmitted through the driveline creating a vibration/drone noise.

Correction

If normal diagnosis fails to determine the cause of the concern, replace the EPROM.

Service Procedure

Refer to the appropriate service manual for the EPROM replacement procedure.

The service EPROM will raise the TCC apply speed to 59 MPH (95 KPH) and the coast down TCC release speed to 57 MPH (92 KPH). This EPROM may effect fuel economy.

Important:
The vibration/drone noise is caused by normal engine vibrations being transmitted through the driveline to the body of the vehicle. When the [1][2]torque converter clutch is applied, the fluid coupling no longer absorbs the engine vibration. The transmission torque converter should not be replaced if a vibration/shudder condition exists AFTER the TCC is applied.





Parts Information

Parts are currently available from GMSPO.

Warranty Information

For vehicles repaired under warranty, use:

Labor Operation Labor Time

TO5OO 0.3 hr