Upper Shock Bracket, Front - Cracks or Separates
Group Ref.: 3 - Steering/SuspensionBulletin No.: 463301
Date: June, 1994
SUBJECT:
FRONT END UPPER SHOCK BRACKET FAILURE (REPLACE BRACKET)
MODELS:
1988-94 CHEVROLET AND GMC TRUCK K3500 MODELS AND K2500 MODELS WITH 8600 GVW RATING (C6P)
CONDITION:
The front-end upper shock bracket may crack and eventually separate from the frame rail on some vehicles. Owners may comment on a poor ride condition or on a noise emanating at the front of the vehicle.
CAUSE:
An investigation has revealed two causes of this condition.
First of all, it was found that some owners may adjust the vehicle's "Z"-height beyond the factory recommended specification in order to obtain additional ground clearance. If the front suspension trim height ("Z"-height) is beyond the factory recommended specification, the front shock absorber will be extended. Under normal driving conditions, the shock absorber will reach its "rebound position" more frequently and damage to the upper shock bracket may result.
The second cause of this condition deals with the after market snow plows. When a snow plow is installed on a vehicle, it is often necessary to adjust the vehicle's "Z"-height in order to obtain additional clearance of the snow plow blade to the ground. This is perfectly acceptable as long as the "Z"-height remains within factory recommended specifications. Many owners, however, fail to re-adjust the "Z"-height when the snow plow is removed from the vehicle. The result is that the "Z"-height may be beyond the factory recommended specification and damage to the upper shock bracket may result.
CORRECTION:
A replacement upper shock bracket should be installed and, if necessary, the "Z"-height should be set to factory recommended specifications following the procedure below.
SERVICE PROCEDURE:
1. Disconnect the negative battery cable.
2. Raise the front of the vehicle and support with suitable safety stands.
3. Remove the wheel and tire assembly.
4. Remove the splash shield.
5. Remove the shock absorber.
6. Cover the inner and outer CV boots, the steering components, and the brake lines with a flame retardant cover.
7. Using a 1/8 inch drill bit, drill a hole through the center of each of the two holes which remain on the portion of the bracket which is still connected to the frame rail (See Figure 2- "Identification Holes"). Drill all the way through the frame rail for each hole. These holes will be used to locate the replacement bracket later.
8. Using an air chisel, roughly chisel off the remaining portion of the bracket still attached to the frame rail.
Note:
The use of a torch to remove the bracket is not recommended. The use of a torch may damage the material properties of the frame resulting in reduced strength.
9. After removing the majority of the bracket from the frame rail, a grinder should be used to remove any excess which remains.
10. Position the new bracket by aligning the holes with the "identification holes drilled in the frame rail in Step 7. Note that the lower hole on the replacement bracket may have to be drilled out in order to see the hole in the frame.
11. Once the bracket is positioned correctly on the frame, install an appropriately sized temporary screw and washer combination through the top hole on the frame bracket and through the identification hole which was drilled in Step 7. Tighten until the bracket is flush against.the frame and no longer needs to be held in the correct position by hand.
12. Temporarily install the shock into position by installing the bolts at the lower control arm and at the shock bracket. Compare the position of the shock and shock bracket with the corresponding parts on the other side of the vehicle. Make adjustments if necessary.
13. In preparation for welding, cover the fuel vapor lines and brake lines behind the upper shock bracket with a metal shield. Also, ensure that other components are protected as suggested in step 6.
14. With the shock and shock bracket still in position, tack weld the fore and aft sides of the bracket.
Note:
Be sure and tack the bracket down on each side and not on the top or bottom of the bracket (Figure 1). High stresses are on the top and bottom of the bracket and any discontinuity in the top or bottom weld is not recommended.
15. Remove the shock from the shock bracket and the lower control arm. Also remove the temporary screw and washer installed in Step 11.
16. Weld the bracket in the positions shown in Figure 1. An arc welder is preferred because of the limited space between the shock bracket and the control arm brackets. Consult the service manual for proper welding instructions.
17. Install the shock absorber. Tighten the nuts to 90 N-m (66 lbs.ft.).
18. Reinstall the splash shield using 5 new fasteners.
19. Install the wheel and tire. Proper torque is shown below for both single and dual wheel models.
K 2500, 3500 (Single) - 60 N-m (120 lbs.ft.)
K 3500 (Dual) - 190 N-m (140 lbs.ft.)
20. Lower the vehicle and reconnect the negative battery cable.
21. Ensure that the vehicle "Z"-height (Figure 3) is set to the factory recommended specification. For snow plow equipped trucks, the "Z"-height should be set with the permanent structure installed and without the snow plow. Recommended specifications can be found on Figure 3. Consult Section 3A-5 of the Service Manual for "Z"-height adjustment instructions.
SERVICE PARTS INFORMATION:
Parts are expected to be available from GMSPO on 6/6/94.