So i bought a 1980 rx7 back in december, original everything. got it for super cheap because of rust and someone attempted to hotwire it so dash was torn apart and missing pieces. Long story short, original engine was shot, bought a used 12a off marketplace. guy didn’t know what year it was out of, but definitely 80s. also found a used trans from an FC, also don’t know what year. Got the engine and trans swap done, everything wired back up (everything that wasn’t already broken), installed the starter from the 1980 engine onto the trans because i new it was good and new engine or trans didn’t come with one, go to turn the key and all i hear is a clunk. short the terminals together with a screwdriver and you can hear it spin, took it off and gave it power and ground, the bendex came out and it spun. but when it’s installed on vehicle it just goes “clunk”. i know i got a massive bag of worms in my hands. any one got any ideas?

 

Need a new starter, probably. Assuming that the engine can rotate.

If the engine can't rotate, did you use the correct slave cylinder bolts? For one of the positions, a too-long bolt will hit the ring gear and keep the engine from turning.

 

I figured i’d need a new starter. just gotta figure out the engine year. and the slave cylinder bolts is a good question. i kept on the slave cylinder that came with the transmission, but since its not really supposed to match up with that engine that might be an issue. i’ll have to check it out

 

or at least the solenoid, bridging the terminals with a screwdriver is basically bypassing the solenoid contacts. it's apparent the key works because the solenoid is kicking out, just not passing power to the starter motor.

 

where is the solenoid located on these things? on my old ford you follow the battery wires straight to it, but the battery wires for the rx7 just go straight to the starter. also i tried looking up where the ground goes to as i wasn’t the one who took everything apart. i found a thread that says it just gets bolted to the bell housing. is that correct?

 

The solenoid is part of the starter, Fords are kind of an outlier in how they have an external solenoid.

IIRC the Mazdas are kind of weird in that they need the motor to drive to kick the solenoid to full contact.

Every RX-7 starter that I've had fail, failed because the brushes rusted in place in the holders. If you aren't afraid of disassembling things, it's easy to fix (and give the commutator a nice polishing with emery cloth held in one fist while cranking the commutator with the other hand) BUT the brushes are somewhat fragile carbon material and they will crumble and break if you just try to pry on them *****-nilly so it requires a lot of patience and a long soak in penetrating oil or a kerosene bath.