I heard it could be done, but wanted to know what's involved...i/e wire from the 4th gear pressure switch to the TCC solenoid so when tranny shifts to OD the TC will lock.

Is this doable? Any issues with doing this like decellerating with the TCC engaged?

 

Chances are your 4th gear switch is N.C., not N.O., so you couldn't use it directly, but you could use a relay. If you don't mind changing things, you could replace the 4th gear switch with a N.O. one and rewire.

 

Thanks for the reply. I'm looking for a way to get around buying a lockup kit.

What's the 4th gear pressure switch used for? Nothing internal to the tranny is it?

 

Nope, just to signal the ECM.

 

Thanks again

Very cool.

Do you think there would be any potential issues decellerating with the TC locked?...Say cruising at 60-70, then coasting with the TC locked up until the downshift occured?

 

No major ones that I can think of, but that doesn't mean there wouldn't be any.

 

I've left the TCC locked in 4th during decel and I could hardly tell. This is because the over-run clutches are not engaged in 4th. So I don't see a problem with that.

Leaving the TCC locked in 3rd felt like I was driving a stick car. Whole different scenario.

RBob.

 

Lol, I'll ask around a bit more. I know the TC stays locked for a bit when I let of the gas in my IROC, but only for a few seconds...don't know if there's a longevity reason for it, or just because that's how they designed it.

Thanks again, now go out and enjoy the 3-day weekend!

 

Yeah, see I'm only concerned with locking in OD, only time it'll be kept in 3rd is in traffic and stop and go driving.

Thanks.

 

About 90% of all 4th gear switches are normally open, & that is what you need for a 4th gear lockup. You will need the GM lockup vacuum solenoid & plugin, to make this work. At medium to slightly light throttle openings, the TC clutch will stay locked up. At very light or WOT throttle openings, the clutch will unlock.

 

Thanks Dana,

The tranny is out of a '91 or 92 RS, should be the same as my '89, huh? I have the Helms for my 89 with the fluid diagram/schematic.

 

Yes.

 

I'm using a switch like this to lock up my 200-4r. It work great. No lock-unlock-lock-unlock cycles at all. The pigtail
was hard to find, however. I have a hot wire to a N.C.
brake switch to a two terminal N.O. 4th gear pressure
switch then to a 700-r4 style grounded TCC lockup
solenoid. The vacuum line for the vacuum switch is connected to full vacuum port at the intake manifold. Pushing the brake pedal or accelerator opens the lockup circuit.

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