jasenr

Would lockup work on a 700R4 with the factory computer or do I need to get an aftermarket lockup controller? Thanks!

7T1vette

Interesting question. Not sure. The 700'R4 had a T.V. cable. If the trans in the car now (350 w/lockup, I think) has a T.V. cable, too, it might work fine. You'd have to try it to find out. The '81 computer made determination of 'when' to drop or apply lockup. If everything feeding that computer information is still in the system, I'd guess that it would work.

ramair_bryan

I added a toggle switch on the console. Flipping it sounds like fifth gear. …..

derekderek

All well and good until you floor it and forget or don't have time to hit unlock switch. Maybe add a throttle lever switch to disconnect at 30% or so. That lock is for low load gas mileage. You could pop it with a Vega motor.

7T1vette

The design of the lockup clutches (and how they work) is essentially the same for the THM-350 and 700-R4 transmissions. Both have a 12vdc signal which activates a solenoid valve to work the clutch. If it were me, I would swap out the transmission and identify the 'hot' pin in the connector for both units and wire the 700-R4 as needed to try using the '81 ECM to do the work.

The ECM most likely (I don't have one or the manual for the '81) turns on a relay to feed 12vdc to the lockup clutch circuit. If that stays with the car when you swap transmissions, wiring the relay output to the proper pin in the elect connector should do the job. If that relay is part of the transmission, you would have to rig up another relay to recreate that part of the circuit. You DO NOT want to attempt to 'drive' the lockup clutch circuit with the ECM output directly. It won't have enough current carrying capability and that part (and possibly more) of the ECM would likely fry and render it useless.

If you hook it up and it doesn't work as expected, you could just stick a lockup controller on the 700-R4 and go merrily on your way. It is worth a try to use the ECM for that purpose....nothing to lose, really.

P.S. Powering the lockup controller (should you need it) is simply to get 12vdc power from the normally-open connection on your brake lamp switch and running it to the 12vdc power input on the controller. So the ECM would no longer be used for that purpose. And, IMO, you NEED to have the lockup clutch managed by something focused on just that purpose. If you leave that task up to human decision, that lockup clutch won't last very long.

fishslayer143

not really an issue..if it only locks in 4th gear ..

Eric P

It should be Vacuum switch on the early 350 , 200R4 and 700R4 , this B&M kit would work
https://www.summitracing.com/parts/bmm-70244

Haggisbash

Not sure about the 700R4 but the 200R4 for a computer controlled transmission came with solenoid switches (3rd and 4th gear) that are held closed by application of voltage, when the computer determines that the lock up clutch should engage power is removed from the solenoid allowing oil pressure to lock the clutch. The manual kits have solenoids that operate by application of power to open them. You can't simply change from one to the other without dropping the pan and changing the solenoid/s.
I opted for a manual engagement master switch for my 200R4 and wired this in series with the N/C contact on the brake light switch, a vacuum switch and an adjustable vacuum timer ( I can incorporate an adjustable time delay to the vac switch to stop the clutch locking/unlocking excessively with on/off throttle applications) . The vacuum switch will disengage the lock up if I forget and start to put too much load on the clutch.

Glenn Leidy

For my 1981 vette I just had a 700r4 installed and the installer used the existing ecm to control the lockup on the 700r4.

jasenr

Thanks for all the great responses! Im gonna give the factory ECM a try but won't work too hard. Im gonna have an aftermarket controller on hand when I do the swap. ;-)