Most likely one or both front engine mounts are collapsed. Typically those are a rubber bushing with a metal sleeve running through the middle of it. That sleeve can break apart from rust or fatigue, especially after 35 years. The parts of those sleeves can stay in position even though they're in multiple pieces, until something is removed, repositioned, altered, etc. Simply lowering the rear of the engine as the transfer case was removed could easily allow the pieces of those sleeves to move around and let that side of the engine sit lower. The rubber part can deteriorate too and tear apart. GM had trouble with their engine mounts breaking in the mid '60s, and as a result, almost every manufacturer now uses a design that prevents the mount from completely coming apart. Even if the rubber tears, the mount will no longer support that side of the engine, but it's trapped inside the metal bracket and can't go very far. It can, however, let the engine drop perhaps an inch or so.
I suspect you just need new engine mounts at the front. That's nothing to grump about with a truck this age. The same thing happens pretty often today on vehicles less than five years old.
Also, it's possible all three mounts were collapsed for a long time and when the transfer case was reinstalled, the shop put a new one under the transmission. After all, a conscientious mechanic wouldn't put a broken part back in if he cares about his reputation and the quality of his repair. That new mount would raise the rear of the engine, and since the "front" mounts are actually close to the center of the engine, it would act like a teeter totter and the front would go down. The result would be the same. You need new front engine mounts.
Thursday, May 21st, 2015 AT 8:42 PM