The motor mounts are ancient and they rubber is as hard a rock, so I decided to change them out.
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I took the pressure off the mounts by using a bottle jack, undid the bolts (VERY hard to access), and removed the motor mounts.
This is what they looked like:
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Which is a problem because this is what NAPA said a 1980 C-10 motor (donor engine) mount should look like (upper half only):
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I need to go out and find the right motor mount now. Any ideas on what motor mount I should ask for? I'm pretty sure this truck originally came with a straight-6, not a V-8.
Also, FYI- a set of motor mounts should last most vehicles 100,000+ miles or at least a decade. These things are just ancient and it's one more thing contributing to the engine running rough.