Hi there! i have a 87 iroc with the TPI and 700r4 trans. I have a probleme with my tcc lockup and the selenoid #14020691 must be the probleme but I can't find it on the car! I think it can be called also the vacuum delay valve, vacuum switch or low vacuum switch. Eather way its called I'm looking for the vacuum valve that engages or disengages the lockup sending or not voltage, depending on vacuum pressure. Can anyone tell me where it is located on the car!?

 

Unless your car was built with no ECM, it didn't have a vac. switch for TCC circuit control.

The TCC circuit is typically done using the ECM based on engine temp. throtle position and other variables, the wiring goes to the driver's side of the trans., the TCC solenoid is in the trans.

 

Ok thx now i know the selenoid is in the trans but i'm sure it as a cacuum switch since it was build with the ECM. I looked where it is usally, on the firewall or near the canistor, under the dash on both sides but can't find it.

 

There are vaccuum switches in an 87 with ECM, none of which have to do with the TCC unless added later.

 

I dont think any have been added later on my car so what does engage or disengage the lockup if its not a vacuum switch?

 

ECM controls the solenoid in the trans:
You might want to elaborate on this question:

 

The probleme i have is that shiffting from 2nd to 3rd the lockup engages to early it kind of chokes up the engine and from 3rd to OD it locks up correctly but as soon as it locks up it reopens and locks up again in a fraction of a second. My 700r4 as been custom built 9 years ago and i managed to break it 2 times since. It as been working great since the last time, that was 3 years ago, but since the end of last summer i started to have trouble with it again. I know its not because of hard driving cause i've been way more gentle with it since. My transmission mecanic changed a pressure switch in it that was leaking this summer and the probleme i have now, seems to have been showing since. BUT from what you are saying about maybe not having a vacuum switch that directly engages or disengages the lockup and that it directly is controled by the ECM, I think it might have something to do with the custom chip i had made at the beggining of this summer... I think it controls shift points and maybe lockup control. my trans is not electronic since its an 87 so is it possible its the chip that does that? Of course i could test with the original or the hypertech i still have if i know this could be the probleme.

 

It sounds like he may have used the wrong pressure switch. They come in both N.O. and N.C. versions. The switch tells the ECM which set of lockup tables and parameters to use. Either in 4th gear (OD), or not in 4th gear.

Note that the pressure switch I am referring to is under the pan. SO other then the TCC not working correctly I wouldn't know how they knew it was leaking. As it will leak into the pan, not out onto the ground.

RBob.

 

Yes the switch is in valvebody, they tested it and saw it was leaking. This guy is 50 years old and have been tearing and rebuiling 700r4 since they exist so i trust is knowledge but i will mention him the 2 versions you are refering to. A couple of weeks ago when they changed the pressure switch initialy they put in a 200. I dont know what the number is for, and this week they tried a 180 that is supposed to retard lockup engagement a bit more but i still have the probleme i described. That's why i think it maybe as to do with the custom chip if it is possible it can cause that kind of probleme. He figured it could be the vaccum switch that is leaking pressure and we were trying to find it on the car and couldn't find it. Since he was very busy I told him i would try and find it or find more infos and that's why i opened this threads to ask you gear heads! Now i've been told there might not be a vacuum switch and it is the ECM that controls lockup directly.

 

If you unplug the TCC wiring plug from the trans. and the issue stops, then hook it back up and put a test light in the cabin, connected to the wire going from the ECM to the trans., which commands TCC activation. If it's not commanding lockup
wired to the plug at the wrong time, go with the internal pressure switch like rBob said.

 

Typical GM car TCC wiring (IIRC some trucks have a vac switch )

 

Ok, did the test with swapping ECM chips, same probleme, shiffting in 3rd seems to lockup to early and choke the engine and in 4th reopens right after locking up for a fraction. I had the tcc wire at the trans unplugged since thursday when i went to my trans guy and it shifts perfectly so the probleme is obviously related to the lockup circuit. I want to have this probleme fixed to not drive all the time with no lockup for all the good reasons they put the lockup system in. Still not sure it does not have a vacuum switch cause if the diaphragm is broken it could cause that kind of probleme. Thx for the graph vetteoz and jmd i'll do the test with the test light.

 

They are 100% correct that it does not have a vacuum switch unless someone installed an aftermarket switch to control your lockup. There are two types of switches at stated before.. N.O. and N.C. (normally open and normally closed). Even though you trust your mechanic, he is capable of making that mistake.. Have him recheck it to ensure it is working right.

 

i know this is a little off this guys topic. but im doin a th350 conversion on a 87 tpi, and i was told to not go with the the lock up convertor style trans? is this a true statement?

 

You're right, it is off-topic.
Search the transmission forum for th350c.
And/or start your own thread.
And then stab me in the eyeballs for yet another castrated no-overdrive car on the road.

 

lol wow. yes sir! hahaha

 

Thx again! if a normaly closed pressure switch was on it, it wouldn't be able to roll no? it would choke up the engine like stoping with a manual trans without pressing on the clutch? Still seeking infos for my probleme, The lockup circuit is rather simple and it sucks that i can't find what the probleme is... The ECM applies voltage to engage lockup on the third and fourth gears, why the hell would it suddenly apply it to quickly on third and resend a second signal on fourth right after it applied perfectly. The selenoid and pressure switch were replaced.

 

In 1st gear, it is hydraulically prevented from locking up. So it will still roll.

So, in a car that slows down to a stop in 2nd and has a *stuck closed* TCC solenoid, it makes it feel like a manual car w/ the clutch engaged until it <bump> goes into 1st, then it's fine.

But if the trans. has a 3rd gear pressure switch, maybe it's wired wrong. When you feel like using a test light to see when the ECM is commanding lockup and checking the pressure switch style (NO, NC) then you'll have more answers.

 

pop the trans pan and check the wiring. you're gonna have to do it eventually, anyways, so you might as well just get it done instead of worrying about a vacuum switch that isn't in your car...

 

Thx guys! i'll check what you told me and answer back!

 

Install a 4th gear pressure switch and loose the ECM control.
TCC will engage anytime ( and only ) when in 4th gear

https://www.thirdgen.org/forums/carb...c-control.html

 

Thx alot vetteoz! please tell me, will doing this taken from the link you posted, will actually cancel ECM control and apply lockup only in fourth gear? or am i missing something. My trans do have a fourth gear pressure switch.

(With an N.O. 4th gear switch, now you have a few options.

The minimal way to get things working now is to just put a jumper between the wires going to pins B and D (light blue and tan/black in the diagram here, your colors may vary) on the factory harness. The solenoid will still get +12v through the factory brake switch as before. When when the transmission shifts into O/D, and the solenoid will be grounded through pin D, pin B, and the switch, completing the circuit to lock the TCC. It's easy at any time to unmolest the factory harness by removing the jumper wire. The TCC will work the same as in the first article posted by whiley, except that the brake switch will unlock the TCC during braking.)

 

More about what the problem seems to be is that, the minimal speed alowed from the ECM to allow lockup is around 65-70 Kmh ( not sure what it is precisely ) and the car reaches that speed in second gear. At that point the ECM sends the voltage signal to apply lockup but it can only engages in third. So that's why when it shifts in third it chokes up the engine cause the lockup is already applied, instead of applying it when in third. Same thing for fourth. We saw it apply voltage in second with the scanner plugged on the ALCL and see the TCC operation all the way to fourth. Dont know if this is happening since the car now as a 3.73 gear instead of 3.27 and since it as rather more power than stock and it reaches 70 Kmh way quicker.

 

Post #8, first sentence.

 

Thx jmd, I know right, seems to always come back to the pressure switch. But since it as been replaced with another kind and since the lockup seems to be engaging relative to speed instead of a gear, i thought it might be something else. It engages in second gear, wouln't the pressure switch allow lockup only in third or fourth from what i read?

 

Lockup is hydraulically impossible in 1st gear in the 700-R4.
You've stated it engages in 2nd gear. Then you ask if lockup is only allowed in 3rd or 4th. To answer that, there are several different wiring schemes used even across ECM-controlled lock-up setups in the 700-R4. Some could prevent lockup outside 3rd or 4th. But it's pretty bloody apparent it has a high potential to be wired incorrectly so referring to a "correct" setup as the status quo in helping troubleshoot doesn't help in this instance.

Sometimes, it helps to look up the lockup schematics for reference and shampoo with the happy red ATF. Not only can you see what's going on, but you can test the switch and quit questioning whether it's NO or NC.

And no offense, but your neck must be really strong.

 

lol I have big head yes :P not that i think i know it all, more in a stubborn way. I respect what you seniors are saying of course. Unfortunetly the car is parked in a tempo at home for the winter and can't really work on it so i'll follow up this spring... Thx