While bench testing a couple of starters that I have, they act perfectly. Connecting to power and ground engages the gear and the starters crank at a pretty high RPM. When I install them in the car, I can connect the wiring and all is good until I cross a screwdriver across the studs, or use the push button that I hooked up in line to test. As soon as I engage the starter in either way, the starter cranks the motor over just fine but will not disengage. The only way to get the starter to stop cranking is to disconnect the battery. Once it's disconnected for a second, I can hook it up again and the same thing repeats.

It certainly sounds like a solenoid problem to me, but one of these starters is brand new (rebuilt). The other one was doing this and I took the solenoid off of yet a third starter that worked correctly electically, but didn't engage the flywheel correctly and still have the problem.

Any ideas?

thanks