Hot Rods 700R4 w/o lockup when warmed up.

Pressure switches for the 700R4 are not inside the trans. They thread into a hole on the passenger side to connect power to the 4th gear solenoid inside so once you let off the throttle the pressure drops and unlocks the converter. These are part of the kit when installing a 700R4 into a older car.

 

I believe that 1990 and later, the pressure switch is mounted on the bottom of the valve body with all wiring internal. At least that's where mine is...

No offense but you are in error about letting off the gas to drop out lock up. The fourth gear pressure switch which controls the hydraulic solenoid closes when you are in fourth gear , and opens when you are not.

 

I'll post this link here, just in case it is needed by OP or another rodder in the future.
https://www.jalopyjournal.com/forum/threads/700r4-torque-converter-control-tcc.1321352/

 

Another way is to wire through the 4th gear pressure switch. @Lloyd's paint & glass can tell you how it worked for him.

 

Weren't there some odd power train and/or vehicle applications where the 700R4 trans had a shift sequence (in drive) of 1st gear, to 2nd gear, to 3rd gear, to converter lock-up and then into overdrive?

 

Probably the "sending unit" that grounds when pressure hits the 4th gear port. If that makes any sense. The guy here pulls the temp sensor and moves it to the 4th gear port, and puts the plug out of the 4th gear port in the temp sensor location. Moved some wires around and in effect, when pressure hits that 4th gear port, it grounds the lock up converter. If that sensor is bad, it won't ground. It looks just like an 3/16"brake line pressure switch. Don't quote me. I'm a half ass body man lmao!

 

1/4-ass

 

Still better than being a total-ass.

 

The only external "connections" on a 700r4 are the 12v electrical circuit to trigger converter clutch lockup, the TV cable to control shift points, and the gear selector. There is also a line pressure port to connect to when checking fluid line pressure Everything else is internal, including the gear pressure switches and the temperature switch (See the pic below of the valve body. Different applications used different switch combinations). I think you are maybe talking about the vacuum switch which is used to control the 12v lockup signal.

Pic from another thread with thanks to @gimpyshotrods

 

You have more patience than me.

 

Here are the 2 switches that I was talking about. They're inside the pan. My transmission guy is Daryl Thompson, about 80 years old, been building transmissions his whole life. He doesn't use a "kit"

 

Just finished the diagnostic cruise. Hooked up a vacuum gauge where I could see it while driving and hooked up a switch to operate (ground) the lockup circuit as some have suggested.

Without activating the ‘override’ switch all symptoms were as before: works fine until several miles into pulling a grade, etc., then it comes out of lockup at high vacuum (as when I let off the gas pedal) and returns to lockup with moderate vacuum (getting back into the throttle); that’s abnormal behavior. Still came out of lockup at 8-10 inches of vacuum as it is designed to.

A few miles later it would never lockup……until I flipped the override switch. I conclude it’s a faulty vacuum module as @pprather and @1971BB427 were first to mention.

I’ll get another one from TCI and report back to close this ticket.

Thanks for all the feedback.

John

 

I think they are pressure switches much like an oil pressure switch. They complete a circuit to the solenoid when the transmission goes into third or fourth gear. There is only one solenoid, and that is the one that applies the torque converter. In the OP’s case he has some kind of vacuum switch. I was suggesting he bypass that and anything else to rule them out.

 

He doesn’t need a kit. He knows how it works and he uses his brain to work around it. That’s how your pose to do it. My T350c is lock up and I just wired it to a toggle switch on my dash. When it goes in the third gear, if I want to, I throw the switch on.

 

Curious. But say you’re doing 40 on a highway. And want to pass, I’d assume you’d have to flip the switch off before the transmission dropped to 2nd?​

 

Nope. The hydraulic circuit for the converter only works in third.

 

If the converter is locked and the trans goes back to 2nd under acceleration does it make the downshift harsh?

 

Yes

 

Nope, because the converter unlocks at the same time as there is no ground circuit for the solenoid. Also, there is no hydraulic flow to the converter control valve unless it’s in third gear

 

The fluid pressure switches for 3rd and 4th gear are in the valve body. The wiring harness for the lockup solenoid runs through them.

Not sure what you’re referring to that screws in from the outside.

 

I believe it can be wired this way. I don’t know if there are any OEM applications that do so.

You’d bypass or eliminate the 4th gear switch, and wire the lockup solenoid to a 3rd gear switch. It’s been a while, but I think I remember mine being set up this way when I got it, along with a weird ass “shift kit” that raised the shift points to stupid levels (2-3 upshift at 75MPH). All of that has been removed, and mine is now wired to work off of the 4th gear switch and a vacuum switch.

 

The best option (subject to individual's temperament) is a dash switch which allows either stock/standard shifting (fourth only), no lockup in any gear, or lockup in 2, 3, and 4. I live in a "hilly" area and it comes in very handy for me. It requires a two pole (N.O.) 4th gear pressure switch, a three position dash switch and some wire and connectors. No "kit" required. I have a wiring diagram if anybody is interested.

 

I'll go with @justpassinthru .
Having the converter locked when you are into it and the trans is kicking down will cause a more severe downshift (4th to 3rd in t700 or 3rd to 2nd in t350). This is the exact reason the manufacturers made the tcc unlock before a downshift. It will contribute to clutch wear and it's ultimate failure. The clutches in these transmissions will not take kindly to much rough treatment.

 

When the diaphragm or spring in the PRESSURE switch, which is located in the valve body, goes bad the torque converter can stay in lock up and yes, the downshifts will be harsh. Drop the pan and replace the pressure switch. It's not hard. Even if you just use a toggle switch, it will still lock up in every gear. The pressure switch tells the logic circuit which gear it's in. When it fails closed, it thinks it's in OD.

 

Yeah, I don’t know man. Works for me.

 

A 90 ish GM Shop manual will easily explain the wiring & fluid circuits operation of the 700 R

 

I have found those are a little difficult to find online. An actual manual will have it for sure. Some of those old manuals were super detailed. Almost like engineering manuals.

 

Yes in last 1O or so yrs, hard to get,
Alot of them where thrown away ,
Some where 1 volume books
Some 4-5 volume sets , per model & year, @ that time I was paying on flea bay , $5- 50 or so ,
I worked @ a G shop , that had a room
Like 30x30 full of just shop manuals,
Just automotive not including equipment Caterpillar Commons
All was cleared out one day around 2005 dumpsters full ,close to where you R @
There is about 7 main shops where you are located

 

Here you go guys. My treat. Straight from my digital storage vault to you. Enjoy.............

 

Yes, I worked for Ford for about 40 years. We had all the manuals pretty well organized in a room. I got some of the old ones when they pushed them out to make room for newer stuff. The new ones are not as detailed. Old ones had color hydraulic schematics that were awesome. Good old days!