75 GMC 3500 Won't crank when hot

75 GMC 3500 dump body 4bbl 350 won't start when hot. Starts fine when cold. After it is run for a bit and it is shut off, it won't crank over. Starter won't engage. Let it cool down, or get the truck rolling (hard to do with a full load) and pop the clutch, it will start.

I'm stumped. I was thinking the starter, but it still operates when the engine cools, or if you pop the clutch. Internal starter components going bad? Thanks for any help!

This is a common problem for older small-block Chevys. The heat from the exhaust heats up the starter motor, which increases the reistance in the copper windings of the soleniod on the starter itself.

You can use a heat shield for the starter. Many SBC's have these stock from the factory, or you can buy them separately. Or you can use header wrap to wrap up the exhaust pipe near the starter.