After a recent tranny rebuild with a new converter installed, I have lockup way too soon. Shop says the computer is doing the lockup, but the same computer worked ok on the three previous converters.
I see this,
**Pull away from a corner when normal 1-2 shift would be at 30 mph with 2/3 throttle. I get lockup about 20 mph and it chirps the tires.
**Driving at 2000 rpm in 3rd, apply throttle and it shifts down to 2. Tach moves to 3700 rpm, car lunges ahead and converter locks up almost immediately pulling rpm back to 3300 and causing engine to bog slightly.

Engine is 406, previous converters were stock (stock tranny), 2200 stahl (Pro Built tranny), and 1900 stahl (Jasper tranny). Current converter is a V6 unit (stahl unknown) (this type converter was recommended by the shop).

 

It's not the converter. It's an electrical or electronic problem. The computer can't control the lockup anymore if you're running a carb on that 406.

 

The convertor lock-up is controlled by the computer, the convertor is not the problem.

 

Still using TPI and same computer that has been on 3 previous tranny/converter setups. Guess I will check/clean connections underneath. If all is well, will start up top.

 

did you ever figure this out?

I am having the same problem now on my 84 t/A. Did a transmission rebuild, added higher stall converter and now I'm locking up at 15-20mph as soon as it shifts into second and the engine is lugging very badly and I'm getting crazy vibrations under the car when it does. The shop that did the rebuild is looking into it but I'm trying to do my on research on it.

 

If the ECM, wiring harness, solenoid, and pressure switches are the same as the last, it will lock up the same as the last. There are normally open and normally closed switches that may be interchanged in error.

 

Only the trans and Converter were changed. All else is the same.

 

If the behavior is corrected by unplugging the TCC plug, then you need to diagnose the TCC circuit, wiring, switching and ECM command routine.

If you find it's not being commanded until 4th gear and approprate ECM inputs (temp at normal operating, stable TPS signal, closed loop?) then you will need to figure out which switch or wiring change is causing it.

The TCC solenoid needs + and - to lock up the converter. With the rare occasion of a worn-out solenoid staying stuck, removing one or the other will unlock the converter.

When unmodified, there should be a pin in the ALDL on any automatic third gen that allows the TCC to be locked on command. I think it's grounded. Search or reference your Helms manual.

I'd recommend observing voltage at the wires at the wiring plug at the trans. with key off, key on, idling slow, and going 50mph on jackstands with a helper as the driver. You'll know what signals are going into the trans.

The pressure switches are 2 types, threaded into circuits, usually 4th gear hydraulic circuit and 3rd gear. But again, these and the wiring varied by years.
If the ground side of the 'noid goes to a normally open pressure switch, it will ground when that hydraulic circuit pressurizes to enact a shift. Using these, it's easy to make a fairly dumb auto-matic lock-up circuit for a non-ECM car.

With that said and done, you'd be about ready to drop the pan, confirm how things are wired up, and how they might be changed to prevent lock-up in 2nd, assuming that's exactly what's happening.

You may prefer deferring to the shop to troubleshoot, or go to the trouble of reviewing the above on your car and figuring it out yourself.

I haven't reviewed my 80s Helms manuals for B platform wiring diagrams for TCC, but if I run across some, I'll scan them in.

 

I'm going through the EXACT SAME problem as you, make any progress?

 

The shop went back I to my trans and disabled the ecm lockup and went with a manual valve body control for the tc lockup. The ecm was commanding lockup way early and the only really way to fix this is to reprogram the ecm lockup command or spend a lot of time fine tuning internals to deal with the computer's command of the lockup. Both of which cost $$$.