Lock-up problem

[Peer81]

My original TH350C also had a lockup now my 700R4 also has one. I check the wiring harness from the 81 and it should fit right away into the 700R4. I don’t remember the exact cablenumber but I think cable A has a constant 12V supply from the ECM. Cable B is the ground cable but also has a 12V supply form the ECM except when the lock-up is active then there is no 12v and the wire is a ground wire (by the ECM). Wire C is for the 4th gear and controlled by the ECM also.
But what is the problem? When putting the lockup connector in the transmission and drive it the 700 want to go as fast as possible into the highest gear with the lockup on. When slowly accelerating on no time I’m in 3rd driving at 800rpm and that isn’t funny! When braking to a stop the trans is getting back into 1st gear and the lockup isn’t active (because the engine isn’t stalling). By accelerating again, same story. When I accelerate harder the problem isn’t that big but in 3rd gear the trans is switching the lockup on and off (or even changing to second gear?). When I manually change to second gear it’s a harder downshift and without the lockup connector attached. When I disconnect the lockup the 700 is shifting very smooth and right as it should be. Feels to my like the lockup is ON about all the time but it shouldn’t. Anybody knows this problem? :confused

Greetings Peter

 

[TimAT]

there were a bunch of different ways GM got the lockup thing working. It sounds like your ECM is telling the TCC to lockup way too soon-

Some of the 700's had a 3rd pressure switch, a 3-4 pulse switch AND a 4th gear switch. Made a wiring nightmare in the trans. IIRC, the 350C just had a 3rd gear switch.

I'd look at how the trans is wired internally- my preference is a single pressure switch for 4th gear. A switch that closes at 45 psi will close the circuit to the solenoid at about 45 MPH. For some reason, GM designed that so road speed and 4th gear pressure at the valve body is real close to 1:1

Some cars/trucks also had a vacuum switch in that TCC circuit too. Not sure about the Vettes

 

[damoroso]

Yep, the 81 has a manifold pressure switch in the TCC circuit. It's on the fire wall on the drivers side, under a small bracket and has a small vacuum line going to it.

 

[Peer81]

I don't think the manifold pressure switch is for the TCC but it's for the ECM that again uses it to control the A/F solenoid (says my service manual).

As I see it, the ECM controls when to put 12v on the lockup system. But when I read Tim's reply the transmission uses different switches that not always react to the ECM's 12v? btw. It's a 90's Corvette 700R4.

Greetings Peter

 

[damoroso]

Your right Peter, the 700 is wired differently than the 350, I wired 12v to a switch I mounted on the console so I could lock mine up when I wanted to. It's another option. I thought the Manifold pressure switch was part of the TCC, I'll have to go back and re-read that section in the manual!

 

[TimAT]

Couple of ways to get there. One, assuming the ECM does control when it locks, all you need to do is add a 2 pin 4th pressure switch to the valve body, then wire the solenoid with that in line. I'm taking a guess that the ECM just supplies the ground and there's 12v at the trans all the time. (That could be backward? Like I said> guessing) Wire that so the ground, (or power) feeds thru the switch on it's way to the solenoid. The ECM will send the signal as normal, but the 4th switch will not close until it hits XX pressure.
The other way is easier, but it also has the potential to cook the trans if you forget- Just feed 12v to the solenoid with a toggle.

 

[Peer81]

If I remember correctly it's 12v at all times to the trans yes. There is also 12v on the ground wire from the ECM to the trans, only when the speed comes above 25mph the ECM cuts the 12v on the groundwire so it becomes the groundwire so the lockup is activated, when you brake the 12v is back on it and the lockup off. That's why a aftermarket lockup set will not work with the ECM because it is working the other way around.

One question for the 4th gear pressure switch, how does that switch know I'm in 4th?

Greetings Peter

 

[TimAT]

The 4th pressure switch is on the valve body- front right corner. 1/8" pipe thread. Some have a plug, some have a switch. Passage is there.

easy quick wiring- 12v to the brake light switch, to a vacuum switch, down to the trans, to the 4th pressure switch, to the solenoid. Ground the other side of the solenoid.
the brake light switch terminals you want to use are closed when the pedal is not being pressed- just opposite of the stop lights.

Found a picture of a valve body-- the plug marked "A" is the 4th pressure point...

http://www.purplesagetradingpost.com/sumner/techinfo/700R4p4.html

 

[Peer81]

That would be easy but I want it difficult.

I did some quick lockup learning last night so I think I know the basics, simply said when the 12v loop is at the right moment closes the converter locks up. Other wise or when driving to slow, braking etc etc the loop is open so no lockup.

As my ECM already controls lockup (in a sort of way) I don't want to put a new 12v lead wire with a brake switch to the A terminal.

At this moment the A terminal has constant 12v.
B should be the high gear switch to the ECM (not D) but my ECM doesn't have this option (altho I have the wire from the B terminal in my wiring harness.
Terminal D is controlled by the ECM with contant 12v under 25mph and when braking. At other times (I have to recheck this) it's a ground wire closing the loop to the tcc solenoid.

As I drive alot in 3rd I would like to lockup that one to, as the 4th gear.

I already have the two wired tcc solenoid original with the 700R4, a 4th (or high) gear switch, a 4th gear pressure switch (don't know which one) and a temperature switch (not a 4-3 downshift switch if I remember correctly).

I think for the 4th gear to lockup correctly I already have all the right parts (except for the right pressure switch). I hope somebody knows where the downshift switch is for as I think the pressure switch does the same or not.
And If I also want to lockup 3rd, I think I'll need a 3rd gear pressure switch and maybe a 3-2 downshift switch?

More theoretical. As terminal A is constant 12v and I only can use terminal D to the ECM (depending if the switches are on the 12v or ground side) put the 3rd and 4th gear pressure switches and (downshift switches?) parallell to each other?
Example. Driving in 3rd, at the right pressure lockup is activated, deactivates when downshifting, 4th gear switch is open.
Driving in 4th gear, 3rd gear switch is open, when again at the right pressure 4th gear switch closes and lockup is activated. Is this realistic?

Greetings Peter

 

[Peer81]

Tim if you could help me by explaining one thing.
I can put a vacuum switch between the positive or ground side of the lockup. When vacuum drops in the intake the lockup will disengage.
I can set the vacuumsignal to a point where it will only lockup when I'm driving at a constant speed so no problem there.

But when I place a 3rd or 4th gear pressure switch, the lockup will engage when the pressure in the valvebody gets higher then set by the pressure switch so it will lockup. I don't know how pressure moves inside the valvebody so will it also disengage when accelerating? I looked in the net but couldn't find pressure switches that have differend pressure points?

For example what I have in mind. I have the 12v side, put a vacuumswitch in there. The 12v becomes terminal A inside the transmission and goes to the lockup, after that on the ground side it splits in two sides one for the 3th gear switch and one for the 4th gear switch, after that they "become" one ground wire again that goes to the 4-3 pulse switch. After that the groundwire exits as terminal D and connects groundwire that also has the brake switch and the "disconnect at <25mph switch" after that it goes to the ECM.

I don't know if I need or if its possible to have a 3rd and 4th gear switch or is there an other way to do this? Well that's maybe more then just one thing...

Greetings Peter

 

[TimAT]

A little "creative" wiring and you'll be on your way.

Add a little wiring and a 3rd pressure switch. Hook the 3rd and 4th in parallel so either one will make the circuit.

You may have to hunt for a pressure switch the closes at the right time- I know that the port for 4th "sees" pressure at nearly 1:1 with road speed. 45MPH is really close to 45PSI (+or-). I dont' recall what the 3rd port sees.

As long as the TCC solenoid gets 12v on one side and a ground on the other, life is good.
Some of the solenoids had a single wire and the ground was inside it, others had 2 wires.

 

[Peer81]

You're right Time,

The wiring isn't the problem, I also happen to have a 88 service manual for a monte carlo/caprice that happens to have 12! different lockup wiring schematics in it.

But still a few questions arise, I see some have a TCC signal switch. What does it do?

Second question, as living in the Netherlands I need to order everything online. I already found a place where to order all the switches but I still need the connectors that connect to the switches (of course I can also ask that online shop if they have them) but does anybody have a link to a shop that has them. And I need special oil and temp resistant wiring?

Greetings Peter

 

[TimAT]

If memory serves, the TCC signal switch is just that- a single wire switch that runs back to the ECM to tell it the TCC has locked. No idea why but that's it. Maybe it tells the ECM to alter the A/F a little?

The connectors - a simple 1/4" female blade will work fine- it'll slip onto the terminal on the switch just fine. Any oil resistant wire will work- 20 gauge (US reference, sorry I don't know what they use in the EU), will be fine. The terminals won't have that plastic insulator on them, but that's kind of a dressing anyway.

If you run into real problems finding the wire and terminals, let me know. I can get them into the EU and then into the mail.

 

[Peer81]

Thank you!

I'll first look around over here and let you know what I've found

Greetings Peter