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Hi, I just wanted to share with you my latest experience with my Corvette 1985 + TH700R4 TCC lockup issue. My transmission had been rebuilt about a year ago.
The clutches where worn out have been replaced. The TC was sent to a shop for a rebuild. Before that I haven’t got a lockup working as it should be. After the build, everything back to normal includes the lockup. This story began 3 months ago. One of the drives I felt and noticed the TCC isn't working anymore. I verified it against the ECM and I was right.
The ECM sends a TCC signal but it is not engaged. I went to the same shop that rebuilt my transmission.
He asked me to buy a new solenoid because it's too old and sometimes tends to fail. After a few weeks, I brought to the shop a new solenoid.
The shop replaced the solenoid but the lockup is still not working. The shop connected another external wire from the transmission towards the car battery. If you apply a ground to the wire, it is supposed to engage the solenoid (when the engine is ON or at least switch is ON). The wire did the trick and engaged the solenoid when it touched the ground. So why does it still not work with the ECM? The shop called me. I brought the car’s FSM. I read that ALDL port “F” should act the same way as the workaround wire.
We took a drive, we connected a wire to ALDL “F” and its other side to a ground when we wanted to engage the TCC. works… but why does the ECM not engage the TCC?
I check the continuity between “F” and wire A7 that connects to the ECM (A7 is TCC control from the ECM. it sends a ground when the TCC lock is met). There is a continuity so why is it still not working. I opened the FSM again and I read that a solenoid resistance should not be below 20 ohms; it can hurt the ECM.
Lucky me I have another ECM unit at home. I replaced the unit and went for a test drive. The TCC lockup starts to work. My theory: The old/faulty solenoid has destroyed the ECM’s drivers that control the TCC lock.
Corvette 1985, TH700R4 TCC issues - SOLVED
