Hot starter issue
 

I have had this problem occur a few times with warmer weather: when my engine is hot, the starter won`t turn at all, although battery is fully charged. I turn the key and nothing happens. When it cools down, problem goes away. The starter was rebuilt ~3 yrs ago. Does this issue ring a bell? Car is 78SC.

Common problem; it's the starter again. Your best bet for a rebuilt unit is a Bosch SR-68X, and even then you might have a hot start problem due to a faulty rebuild/solenoid.

Your option is to buy a new high-torque unit from Performance Products or similar (Pelican???). FYI: I put one of those in my SC race car and had the hot start problem on pre-grid! The warranty replacement never let me down after that...

It's called heat soaking.
One theory:
A coil of wire (inside the solenoid) that pulls in the starter gear gets hot and the resistance goes down so that it pulls lots of current but gives almost no magnetic pull.
Another theory:
The connections inside the starter get hot and the resistance changes because of the expansion of metal (no or reduced current flow).
I have seen both examples....but the end result...get a new starter.
I would recommend a high output (torque) starter simply because you have more guts to start with and when it gets hot and goes downwards in torque...you still have enough left to start the car.
Bob

gets hot, resistance increases, drawing high current, increasing voltage loss so the solenoid doesn't trip

Had the same problem with a rebuilt Bosch starter. Did what Peter recommends and went with one of the aftermarket high-torque starters.

Sorry for the hijack, but my 72 was in storage for a few months and when I went to start it made that wonderful noise only a starter can make, kind of like your motor just seized. Anyways, for some reason the noise is getting less and less when I go to start, but it's still kind of obnoxious. The started has probably less then 15k on it as I replaced it about 10 years ago with a new one. It has no issues starting the car except the noise. It also has a hot start relay kit just in case. Could it be just the solenoid, or is this a one piece unit?
Is there anything I can do except replace which if I can remember was a real fun job do to a bolt being in a great spot?
Thanks

when resistance goes up, current goes down.

think of it this way. if you connect a wire from the pos to the neg of battery, you will have max current for as long as you can hold that wire there or it melts.
now, put a small resistance like a light bulb on one end and connect the same wire and bulb to battery. the results are a lot less interesting.

one thing you can try if you know how to solder is, this is the condensed version, remove the end of the solenoid, the one with the terminals. pull out the 2 studs, clean them and rotate them 180 deg. clean the contact on the solenoid itself and reinstall. the contacts get burned and pitted. i have revived quite a few this way.

also read this.

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/autbat.html#c1

clean ALL connections. including all grounds. ( that are related to hi current and/or starting)

I installed a high amp momentary switch solenoid jump in engine compartment for this rare heated starter occasion.

works every time for me

The only thing that cured my hot start problem was a Bosch rebuilt starter.

Thank you all for your input. It looks like the solenoid could be culprit here. I will see if I can rebuild or replace it first. Found this interesting thread on that topic.