Hello, hoping someone with more knowledge than I have on the 700R4 lock up torque converter can answer a question. Trans works great as does the torque converter & will lock in 3rd & 4th. Have 12v going to the trans for lockup controlled with a push button switch on the shift knob, goes through the brake switch & has a led to indicate when locked. Questions is what controls the solenoid to unlock when under put under a load? Can accelerate in 3rd or 4th & the converter unlocks, back off & it locks again. Ive seen vacuum switches for sale that will do this to unlock the converter & I have no vacuum switch, so it is internal to the trans. Is there a pressure switch that can interrupt power the lock up solenoid? I don't have any history on the trans other than it had been rebuilt, but what was done is unknown. Only changes I have made is the throttle valve sleeve/piston & spring to raise the 4th to 3rd downshift & governor weights/springs to raise the shift points. Any ideas on what controls the converter unlock is appreciated.

Firstly a query - how how come your car has a 700 R4 fitted? The standard transmission for 85 - 88 MCSS is a 200 4R. The 700 was never fitted as standard to 4th gen MCSS's.

A 700 R4 does not use any form of vacuum switches (neither does the 200 4R). The earlier TH350 fitted to 83 and 84 models did use a vacuum modulator valve IIRC.

As for what causes the converter to unlock (in a 200 4R), I think it is all done via the ECM. The converter locks in a standard CCC equipped car when the transmission is in 4th and the ECM sees a very stable TPS reading (also when other parameters are met i.e. engine is up to temperature). A sudden change in TPS reading, i.e. accelerator.is kicked down and / or the transmission shifts down to third, will cause the ECM to send a signal to unlock the converter. I am not certain, though the TV cable may also play a part.

If the computer has been removed from your car, which is possibly why you have the lock up switch on your shift lever, then I don't know what is causing the converter to unlock. Does your car still run with the ECM and CCC Quadrajet?

ChasUno, he's talking about an aftermarket vacuum switch that opens the circuit when vacuum goes low ,like on acceleration, it opens the electrical circuit and the trans unlocks when there is no voltage.

No Computer, No 305, No vacuum switch, No carb, No cats. The car has a 700R4 because that is what I put in it. I know that no 700R4 or 2004R's came with any kind of vacuum switch for tq unlock, but there are some out there just for that purpose. As far as the TV cable, it may play a part in unlocking the converter, I don't know. If it does then it would only be in relation to a change in/or a re direction of pressure. I'm trying to find out what causes the converter to unlock that is internal to the transmission.

I fairly sure that for a standard (200 4R) transmission running with the ECM and CCC Quadrajet, the torque converter is locked and unlocked electronically via the ECM. The 700 R4 is of the same era as the 200 4R, and was fitted to other GM cars also fitted with ECM's (i.e. 3rd gen Camaros). I assume it operates in a similar fashion.

As your car has no computer and a manual TCC switch, then logic seems to suggest that the only things that can trigger a TCC unlock (other than the manual switch or the brake pedal switch,) is the TV cable or the transmission shifting down gears. You mention that your car locks up in 3rd as well as 4th, which is different to the 200 4R that only allows lock up when in 4th. Maybe there is some kind of internal valve in the 700 R4 that also triggers the solenoid?

Not a auto trans guy but getting the converter to lock/unlock is simply as putting 12+ to the solenoid in the trans. Getting it to do that seamlessly without driver input is another thing. Lots of wiring diagrams and kits available to do that. Here's one way to do it using a vac switch and brake pedal switch, couple relays.
https://personligcoach.info/img/200...00r4-converter-lockup-wiring-diagram.jpg

Bob

I dug out my GM service manuals (1988 Caprice and Monte Carlo) and did some reading. These manuals also include details on the 700 R4 trans as well as the 200 4R.

Looking at the electrical manual, there doesn't appear to be anything electrical for TCC operation other than 3rd and 4th gear switches (outside of any ECM operation). I couldn't find anything that indicates that the TV cable triggers any switches in the trans.



Looking in the big GM service manual, that seems to be confirmed when looking at the 700 R4 TCC transmission section (n.b., there appears to be numerous variations of electrical wiring types for this system, but they all seem to center on 3rd and 4th gear switches inside the transmission itself).





As you aren't running the ECM and have a manual TCC switch, it seems that only 3rd and 4th gear switches can affect TCC operation. My understanding of looking at the wiring diagram is that the 4th gear switch needs to be closed for TCC to operate. I can't tell if it will lock in both 3rd and 4th, but there's a lot of mentioning of a 4th to 3rd downshift, which I think operates a switch that causes the electrical supply to the TCC solenoid to be cut, thus disengaging the TCC. Once the transmission moves back up into 4th, then the circuit is once more completed and the TCC is engaged.

Thanks for the input. It does lock in 3rd & then will unlock when a load is applied and does the same in 4th. Have to assume that at some point a switch controlled by pressure or something was changed in order for it to unlock. It works good & have no complaints. Just was thinking maybe someone on the sight had seen or heard how it can be done without a computer or a vacuum switch. Ill use the diagrams you posted & see if I can find anything obvious.

It can be done with a toggle switch, but requires driver turning the switch on and off.

Found some more details about the700 R4 TCC and lock up operation in my GM Service Manual. Some of the information is scattered around a bit, so it took a good bit of reading to locate some of the specifics.

Introduction to the TCC:






Diagnostics:






What I understand, is that these circuit diagrams show that for a standard ECM equipped car to engage TCC lock up, the following conditions must be met:

1. VSS (speed) - must be greater that a specified amount
2. Engine Coolant - must be at normal operating temperature
3. TPS (throttle position sensor) must be showing a steady reading
4. 4th gear switch in transmission must be engaged
5. Brake pedal must be off

If these five conditions are met, then the ECM sends the signal to activate the TCC lock up solenoid and allow lock up to occur. If anyone of these conditions deviates from its specific parameters, then TCC lock up will disengage.

However, in the case of a car with the ECM removed, then the first four parameters do not come into play. The manual switch you have effectively bypasses these four requirement and activates the lock up solenoid regardless of these conditions. The last parameter does still apply though, so if you have the the TCC engaged and then you press the brake pedal, that interrupts the solenoid by breaking the circuit. As soon as the brake pedal is released, then the circuit is completed and the solenoid will re-lock the TCC. Unlike the 200 4R, the 700 R4 uses the 4th gear switch in the transmission to tell the ECM it is in 4th gear, and then then ECM reads the other 3 parameters to decide if conditions are met for it to engage the solenoid. However, there is no ECM input in your car so this does not apply.

Therefore the only way the transmission will come out of a manually activated lock up is if it changes down a gear from 4th. Then the internal 4th gear selected (or 4 - 3 downshift) switch in the transmission will trip, and interrupt the power supply to the lock up solenoid. The only bit in the manual that I don't quite understand is this:

"A 4th gear switch (mounted in the transmission) opens when the trans shifts into 4th gear and this switch is used by the ECM to modify TCC lock up and unlock points, when in a 4 - 3 downshift maneuver."

I get that the ECM wants the trans to be in 4th before it allows lock-up, but I'm not sure what it means by adding "when in a 4 - 3 downshift maneuver"? If it downshifts from 4 -3, then the 4th gear switch will be deactivated? Or maybe it does something specific during the 4 - 3 downshift? Again though, with no ECM in place, this wouldn't occur with a manually activated TCC lock up.The only way a manual TCC lock up can be disengaged is if the brake pedal is pressed, the transmission drops out of 4th gear or the driver deactivates the manual TCC switch.

Alot of good info, thanks. I still have no idea what tells the TCC to unlock under a load with no computer or vacuum switch installed. It will lock up in 2nd, 3rd & 4th when the the switch is activated & supply's 12V to TCC soleniod. In 3rd or 4th with TC locked, give it a bit of throttle & it unlocks, maintain the same throttle setting & when the speed catches up & not adding torque, it locks again. Don't know about in 2nd, no reason to use it. If in 3rd with the TC locked & with a manual shift to 4th, it does not unlock. An auto 3-4 shift & TC locked is the same, no unlock. A forced 4 -3 shift it will unlock. A manual 4 - 3 shift it will stay locked if off the gas or if power is maintained. I don't know how or where it takes place, but the unlock has to be controlled by pressure since there is nothing other than a on/off switch & brake to interrupt power to unlock. There is a single wire under the pan from where power comes in to what I assume is the 4th gear switch & from there to the TCC solenoid. It's a mystery to me & didn't give it a thought until I did the manual lock up & was curious as to why I didn't a vacuum switch.

I Just thought about some info that may help someone down the road. While trying to figure out this unlock mystery & wanting to take a closer look under the pan, I decided to toss the oil weeping steel pan & use a cast aluminum one. Done, no leaks. Was a couple days later & all was fine until after a few miles I noticed that when I slowed enough for the trans to shift to 3rd & then would not shift to 4th again. Decided that changing the pan, filter & oil & no 4th was a coincidence only, one had nothing to do the other. Wrong again. If you scroll up, ChasUno was kind enough to post some pages from a 700R4 manual. Fig 44 is a drawing of the pan. On the bottom of the drawing & to the left is a half circle indentation on the pan rail. The new cast aluminum ebay pan I installed does not have this relief. I didn't realize this until I removed the pan and found that nice new chinese rubber gasket had squeezed out just enough to cover a bleed hole & since there was no indentation in the pan, the bleed hole was blocked off causing the no shift to 4th.