Must have been more prevalent than people remember. TSB issued in December of 1989:
Frame - Cracking Under Severe Useage
GMC NUMBER: 87-2-121
GROUP: 2 Frame-Bumper Sheet Metal
DATE: December, 1989
CORPORATE NUMBER: 962002
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SUBJECT: FRAME REPAIR PROCEDURE
MODELS: 1985-86 K1 AND 1987 V1 TRUCKS
Under severe vehicle usage operations, some 1985-86 K1 and 1987 V1 trucks may exhibit a frame crack at the unused holes between the front shock
and engine mount (See Figure 1). The crack may start in the top flange.
If this condition is encountered, the crack should be cleaned and welded and both frame rails repaired using the fohowing parts and procedures.
Parts Information
Part Number Description
15646904 Kit - Containing right & left frame
brace and attaching parts and graphics.
I have the welding procedure for the repair if you want it.
Here it is, there are no images so it's an easy post:
Welding Procedure
(See Step 4 in Left Hand and Step 6 in Right Hand Bracket Installation Procedures) When gas metal arc welding (GMAW), use Electrode E705-3. When shielded metal arc welding (SMAW), use Electrode E7018.
* Clean as necessary with a stiff wire brush and a clean rag.
* Determine the inner end(s) of the crack by cleaning and grinding the surface.
* Drill a 1/8" hole at the end(s) of crack as an aid to stop crack progress.
* Grind a V-groove along entire length of crack.
* Weld the V-groove completely, filling the entire length past the hole(s) by 1/4".
* Grind smooth to allow tight reinforcement fit.
Note: After the crack was arrested and welded, the repair was not complete. The procedure called for a doubler (reinforcing bracket ) to be bolted to the top flange of the frame rail.
If the crack was in the RH rail, you know those bolts and nuts that clamp the gas line (and that last battery cable clip before the cable crosses over to the engine block)? That is where the bracket was added:
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