I'm getting some abnormal TCC Lock-Up on my car and was hoping someone here could chime in with some answers.

I had my transmission rebuilt with the Transgo 2&3 stick only option to convert the valvebody to full manual. I love the setup, but It's shed some light on this TCC situation. The TCC behaved like this prior to the rebuild, but it wasn't until the full manual conversion that I realized just how bothersome it was.

When I picked my car up from the trans builder, he said that he had unplugged the lock-up harness due to some strange results. Tonight I plugged it back up while I was changing my oil and immediately realized why he had left it unplugged. Basically what's going on, is the TCC will ALWAYS lock in any gear but 1st (I'm aware that the design of the 700R4 prevents lockup in 1st gear) at any speed. If I shift from 1st to 2nd at low or mid-low RPM, the TCC locks as soon as 2nd engages and bogs the motor down plus it causes the car to buck like you were driving a manual and had let the clutch right out. In fact, I did a little test by starting with the trans in 2nd (Don't worry I know all about not starting in 3rd or 4th), and as soon as I touched the gas the TCC locked and stalled the engine. It will still unlock as normal if you hammer the throttle or press the brake.

Is this normal? I thought the ECM prevented lock-up until a certain MPH speed. Something else I've also noticed IIRC is that the TCC override via the ALDL port does NOT work. With the pins shorted it will still unlock when you get on it.

 

Really? Nobody knows?

 

I dont' have alot of information, its been a while since i looked at the TCC lockup tables. But its basically a load vs mph table in the ECM if I remember correction.

From what I remember TCC doesn't lock in 1st, or 2nd, but will lock in D above 37mph, and OD above 43mph or so. And will always lock up at about 75mph even at WOT. I think it can be bypassed by jumping to terminals on the ALDL connector, but can't remember the terminals to use. I think this was for locking them. Perhaps the circuit is getting grounded somehow?

 

I have these diagrams for TPI cars.

 

Good possibility that the ECM is bad. The '85 ECM uses a quad driver that will fry. If it failed shorted the TCC will do what it is doing.

To check it try this: key-on, engine-off, measure the voltage at the ALDL connector pin F. It should be at 12 volts (battery voltage). If it is closer to 0 volts either the wire is shorted to ground or the ECM is bad.

Pull the ECM down and pull the cover. Look for a damaged chip. The quad drivers will be a 16-pin chip located near the harness connectors. Can usually see right off if they are damaged.

If so be sure to measure the solenoid resistance of the various devices. One will be shorted which is what took out the quad driver.

RBob.

 

Went out and measured the F terminal on the ALDL. Couldn't get a reading. I then tried swapping in a spare 85 ECM and the problem continued. Weird part is I don't remember the car behaving like this when I first got it. I only recall it beginning after picking it up from a shop that just did a tranny install.

 

I'd drop the pan and check the TCC wiring. Most likely it is hot wired or shorted in the tranny (insulation rubbed through).

There are a bunch of different ways that GM wired the TCC solenoid. One includes an oil temperature switch that when too hot locks the TCC.

RBob.

 

Is there a way to test for voltage at the lockup harness where it plugs into the transmission? I was able to back my car up on a curb and gain full access to the TCC harness thanks to my 28" tires (Man I'm gonna miss those guys when I get a shorter sidewall), but wasn't sure which wire to probe so I left it alone for now.

I am a bit concerned the body wiring may be shorted somewhere since I can't get a 12V reading at the ALDL terminal. Even with the TCC harness disconnected from the trans, with the key on I cannot get a 12V reading off the F terminal. Correct me if I'm wrong but something doesn't sound right.

Also, if the lockup wiring was shorted inside the transmission, it is to my understanding that with the TCC in a force locked state IE the ALDL shorted the TCC will remain locked under all conditions (Except for the brake switch), however it still unlocks at WOT. BTW, when I say WOT I mean just that. Even under heavy acceleration the TCC will NOT unlock. You have to hold it to the floor for that to happen.

Right now I have the harness unplugged because low speed driving through parking lots in anything except 1st gear is pretty terrible, and if I downshift from 3rd to 2nd (I engine brake through the gears every time I slow down of come to a stop to avoid starting my trans in 3rd or 4th and damaging the clutches) without tapping the brake first it engages like a clutch dump and I don't think this is too good for the driveline.

It wouldn't be beneath me to wire up a switch to manually control the TCC, however like I said that is supposedly our problem right now that the wiring is shorted somewhere forcing 24/7 lockup, however something doesn't seem right because it still unlocks at WOT. Whether or not I wire a manual switch or find the cause of the 24/7 lockup and regain proper computer control I want to correct the problem first. Now I just want to narrow it down to the body wiring or the internal wiring. Which wire do I probe at the TCC harness to see if it is getting the 12V lockup current from a body wiring short?

EDIT: Looking at that diagram, it appears that the TCC control circuit originates from the brake switch via a purple/black wire and makes It's way down to the trans harness. It then looks like it makes It's way throughout the internal wiring then exits out of the trans and back to the body via the tan/black wire which grounds out at the ECM, with the ALDL circuit before the ECM as a shortcut ground for manual lockup. Should the ground wire still be tan/black down at the transmission harness? Maybe It's because it was 2AM and all I had was an LED flashlight, or maybe It's from 26 years of road grime, but I could have sworn the closest resemblence I saw while I was under there was an orang(ish) wire with no stripe. I also saw the purple wire, but there was a third wire as well which, IIRC was pink. What does this wire do?

Also, if it is worth anything I was reading Aperion's TCC article and it looks like depending on the type of wiring setup used, governor pressure was utilized on some setups to determine when an appropriate time was to lock the TCC. With the transgo 2&3 stick only kit I have installed, there is a spring that goes on the governor that puts it at full pressure 24/7 so when you hit the shifter It's always going to go straight into the next gear.

 

The third wire is for the 4th gear switch. This tells the ECM when the trans is in 4th, so it can switch to a different lockup table in the calibration.

Since you can't get a reading on pin F (ALDL) the TCC solenoid is grounded inside the tranny.

To verify, plug the trans connector back in and unplug the ECM. At key-on, engine-off measure pin F (do not depress the brake pedal).

If no 12 volts then need to drop the pan and see how they wired the TCC solenoid. Then re-wire it so that it is correct.

RBob.