my3rdgen

What are the differences in the PSI switches (in valve body) GM used in their 700R4 trannies?

I have seen on other sites that there are different PSI switches. Are they all "NO/PSI Close" switches with different PSI raitings? Or are some of them "NC/PSI Open"?

I want to wire my tranny so that the TC only locks up in OD (no ECM anymore). I plan on getting power from an ignition source, through the lock up switch on the brake pedal, then down to a TH400 style connector pin (GM PN #24205373) on the tranny wired to the PSI switch & solenoid.

I want to know if I can just use the factory PSI switch. I don't want to spend the extra $40.00+ bucks on something I can just wire myself. (I profess DIY)

It would seem like if my existing switch is "NO/PSI Close" I should be able to use it (I havent checked it yet). Am I correct?

Any input would be great.

This car is for weekend cruizing in nice weather. I will be manualy shifting (Megashifter). So a low vac switch is not required for my application.

Apeiron

You mean the 4th gear switch? In thirdgens they're all NC, but in other cars they're NO. My transmission is a 4L60 out of a 9C1 Caprice and it has a NO switch and a temperature switch. I have the part number around somewhere.

IROCZZ3

I did the same thing you wanna do. I referenced this site...http://www.highperformancecars.com/crosley/lockup1.htm

Also it's not really necessary to use a Turbo 400 single blade connector, unless you wanna clean up some wiring. I use the stock 4 pin connector and just cut off the the unused wires. You only need the one that runs through your brake switch. (sorry don't remember which one)

Do you have a rebuilt tranny? Mine is a ProBuilt and it just happened to have a NO 4th gear switch...cost to convert to 4th gear only lockup==> free!

Apeiron

If you keep the factory 4 pin connector you don't have to do as much butchering of the factory harness.

jfreeman74

Not all of those valves are the same. The one that I had in my 700R4 before it died was NO. When I bought a new transmission it had a NC in it. The first transmission was one from '85. I think they changed in 86 or 87.

my3rdgen

I rebuilt it myself with the help of my Dad. He is an old Allison tranny mechanic. I took it over to his place and tore it all apart and rebuilt it with his supervision. It was nice to have some one who has rebuilt transmissions before with me to help.

I used an Art Carr, stator suport, input shaft, and drum with one of their beast shells, 5 gear front and rear planets, corvette servo, "B-Car Fix" from GM which allows a WOT upshift into OD, TCI rebuild kit with a kevlar band, a custom machined TV sleeve (90% to kick down), .500 boost valve, the stock 10 vane pump, a 2500RPM converter, new bushings, and I topped it all off with a B&M SHIFT KIT! (That's like saying I put a rotten cherry on top of a tripple fudge sundae)

I got lucky and only had to change one "selective" part (I think it was the selective plate for the forward clutch). Got it from GM for $12.00 and had it in a week.

It was a lot of fun to rebuild it and know what is going on in there, there were some things that sucked about the rebuild like getting the dang seals in place, and fightin with Dad over the heater, but it was worth it.

my3rdgen

That is what I was wondering about. When/if I ever get time to get back to work on the car, I will see if mine is NO, if so I will try to use the one I have. If its NC, I have part #s for the GM NO piece.

Apeiron

Here's the factory wiring diagram for the 700R4 in V8-equipped thirdgens. The V6 was similar, but without the 4-3 pulse switch. Some later V8 transmissions also came with the 4-3 pulse switch omitted or disconnected to eliminate flaring when downshifting.


The GM P/N for the 4 prong plug is 1208553, and the NO pressure switch is 8627332 or 8642473. If you want to use a vacuum switch you can use a 14014519.

my3rdgen

The solenoids are all the same in all 700R4's correct? They all require power to engage the lock up and not the other way around? This is what is puzzling me. Because how would GM make a NC switch work in that situation if the solenoid has to be powered up to engage the clutch? Are the valve bodies differen't?

I have no clue how that would work

Maybe I am focusing too much on the NC switch and need to just forget about it. I just want to understand how the NC switch system worked in order to better understand what I can do with the Lock Up using a NO switch. I just have to get under the car later today and see wich switch I have first.

my3rdgen

I checked mine and it is Normaly Closed.

Apeiron

The 4th gear switch has nothing to do with locking up the TCC, it only tells the ECM that the transmission is in 4th. Based on that and other sensors, such as the VSS, MAP and CTS, the ECM makes the decision to lock or unlock the TCC, which it does by grounding pin D.

If you still have the factory wiring harness, replace the NC 4th gear switch with a 8642473 single terminal NO switch, and connect the wires to pins B and D together (outside the transmission or inside, your choice). This will make the TCC lock up only in 4th gear, and retains the function of the brake switch to unlock the TCC when the brakes are applied. If you want, instead of connecting pins B and C you could also use a 14014519 vacuum switch between them which will unlock the TCC when you open the throttle in 4th gear.

You can also control lockup without changing the NC switch inside the transmission by using a relay. Connect the relay coil to pin B and a switched 12v source, and the NC contacts on the relay to ground and pin D. Again if you want you could use a vacuum switch between ground and pin D.

my3rdgen

Thankyou! I now understand! I was under the impression that the 4th gear psi switch actually locked and unlocked the TC. It all makes sense now. The ECM is looking for the signal or lack of from the psi switch, and how it is programmed determines which switch is required. But for a non-ecm application I need to use a NO switch and wire it thru the switch directly.

Once again, thankyou.

Apeiron

In the interests of completeness, there is yet another way to add a 4th gear switch without modifying the internal wiring inside the transmission. There is a test port for 4th gear apply pressure on the right side of the transmission. Some years of 4wd gas and diesel pickups with California emissions had a NO switch here to bleed EGR in 4th gear. I don't have a part number, but such a switch could be wired in between ground and pin D.

nikileg

I did check out your site as you suggested. He doesn't say how 4th gear unlocks. I get how to rewire the 700r4 to lock up in 4th only but want to know how it unlocks. I've seen other posts that make it msound like you unlock when you hit the brake. Is this true? I have a ncc set up in my 84 camaro with a new 350 and no ecm. Am looking for a less expensive way of convertin the tranny so nit doesnt over heat in 4th. not a race machine but daily cruiser. Any help would be appreciated.

Apeiron

How it unlocks? Well, then the transmission downshifts out of 4th, there'd be no pressure in the 4th gear circuit and it would unlock. The +12v power is also supplied through a switch on the brake pedal which opens when the brakes are applied, which also unlocks the TCC.

my3rdgen

I second that.

DNSTA

O.K. I'm going to resurrect this thread. I'm attempting to wire my TCC per the instructions above and am having a little trouble. I have both the 4th gear switch and the 4/3 downshift switch. The 4th gear switch has one connector on it. As I read, I do not want to use the 4/3 switch so I need to wire it out of the system. Here it is as I understand it.

I need to run a switched 12v wire to the pedal switch which will interrupt the 12v signal when the pedal is pressed. That I know.

Then I need to run that wire through the 4 pin connector to the 12v wire of the solenoid.

Here is where I am confused. I checked the 4th gear switch by testing continuity to find that, as it sits on the bench, the circuit is not continuous. Therefore the switch must be NO right?

If that is the case, and when the switch closes it grounds, I should just hook the ground wire from the solenoid to the switch and when I hit 4th gear the switch closes, gives the solenoid a ground, and locks the TC up.

Seems to simple. Where am I going wrong?

Apeiron

That would work fine.

DNSTA

Sweet. I've seen other diagrams but never one like the one I described. Seems simple. I'll wire it up tonight. Thanx Aperion.

OS3Fleming

iTrader: (2)

I got this kit that has a PSI switch and harness with an @$$ load of wire. I know where the switch and harness go, but wiring it I have no clue. Can some one paint me a picture and brighten my day.

OS3Fleming

iTrader: (2)

bump

my3rdgen

All of the "extra" wire is (I believe) so that you can get a 12V signal to the tranny so that you can fire the solenoid. Just make sure it is wired through the switch on the brake pedal.

I can't remember all of the details but I did some questioning around 4 years ago so if you do a search for all of my posts back then you will find that I got a lot of help from the guys here, and you might get the answers to your questions.

03proxr

I have a 91 gmc truck that i am converting over to carb i am leavin the comp in an only usin waht i need i bought a vacumn kit but i have to tap into the servo to hook it up and i don't want to do that i was told i could just use a toggle switch for the torque converter lockup....can someone shed a little light on how i need to hook this up and how to use it? i was assumin all i have to do is take the wire in pin A and interupt the circuit with a toggle switch an switch closed would lock it up an open it wouldn't be locked up thanks