Drivetrain - Launch Shudder, Install Additional Mount
Group Ref.: Drive AxleBulletin No.: 164101
Date: October, 1993
SUBJECT:
LAUNCH SHUDDER (INSTALL ADDITIONAL MOUNT)
MODELS:
1988-93 CHEVROLET AND GMC K1, 2 EXTENDED CAB WITH 8 FOOT BOX (MODELS K10953, K20953)
THIS BULLETIN IS BEING REVISED TO ADD THE 1993 MODEL YEAR, ADD K2 TRUCKS, AND CHANGE THE CORRECTION, SERVICE PROCEDURE AND WARRANTY INFORMATION SECTIONS.
PLEASE DISCARD PREVIOUS DIVISIONAL PUBLICATIONS:
CONDITION:
Some owners may comment that their vehicle experiences a launch shudder condition. This condition usually occurs from 0 through about 10 mph and is usually more noticeable during hard acceleration, when the vehicle is heavily loaded or when towing.
CAUSE:
This condition is caused by the propeller shaft U-joints working at high torque and angle under acceleration and results in a shudder or vibration.
CORRECTION:
This condition may be corrected by installing a mount between the transfer case extension and the torsion bar support crossmember.
SERVICE PROCEDURE: (Figure 1)
1. Raise vehicle on hoist.
2. Install the rubber insulator around the transfer case extension and slide the retainer over the rubber insulator.
3. Loosely bolt the retainer to the bracket. The retainer should be bolted to the forward bracket holes for a 4L60 or 4L60-E transmission and the rearward bracket holes for a 3L80 or 4L80-E transmission.
4. Mark the left-to-right hole locations by aligning the bracket flat against the rear side and parallel with the bottom edge of the torsion bar support crossmember.
5. Drill a 13 mm (1/2") hole through both locations and both faces of the torsion bar support crossmember.
Important:
The holes through the torsion bar support crossmember must be parallel and equally spaced through both faces. If they aren't, it may be difficult to install the spacer.
6. Place the spacer inside the torsion bar crossmember, align the fastener holes (two places) and insert two bolts through from the front of the torsion bar crossmember.
7. Install the bracket to the torsion bar support crossmember using the two installed bolts. Align the bracket parallel with the crossmember and install the washers and nuts. Torque the bracket-to-crossmember fasteners to 70 N-m (52 lbs.ft.).
8. Torque the retainer-to-bracket fasteners to 45 N-m (33 lbs.ft.).
Important:
Be sure the metal retainer and bracket do not touch the transfer case. Metal-to-metal contact will create a ground-out condition and may cause noise or vibration.
SERVICE PARTS INFORMATION
Parts are currently available from GMSPO.
WARRANTY INFORMATION
For vehicles repaired under warranty, use:
Labor Operation: T7356
Labor Time: 0.4 hrs.