Lockup and tv 700r4 transmission

[K10-Kansas]

I may have unknowingly removed the some of the wiring for the lockup when removing the old harness. If i did, this lockup wire may have been on the brake pedal or running to something else.

1) Do 700r4 transmissions always have a lockup wire?
2) Also, the lockup wire connects to the brake pedal switch?
3) What does the brake pedal switch have to do with 4th gear?
4) What would a lockup wire connect to if not to a brake switch?



Back story and reason for post above if you want to read it:

(I bought a 71 c10 on a 77 K10 chassis a few states away with a blown engine and bad transmission. I had a local mechanic in that state put in a blueprint crate fully dressed 350 carbureted engine and a new 700r4 automatic transmission. Turned out, all the wiring in the truck was a disaster so I trailered it home and began putting in a complete AAW wiring harness. I pulled all wiring out but left some wires connected to the engine area and transmission because I didn't know what they were. I'm 90% done and am now trying to remember if the brake pedal switch had just brake lights attached or also had a lockup wire or if that blue wire running from the transmission was connected somewhere else.)

[AussieinNC]

To answer your questions...

1) Do 700r4 transmissions always have a lockup wire?
YES if you want it to lock up

2) Also, the lockup wire connects to the brake pedal switch?
YES

3) What does the brake pedal switch have to do with 4th gear?
Nothing...as 4th gear is not the same as convertor lockup
The brake pedal switch interrupts the lockup circuit when pedal is pushed to enable the convertor to disconnect...otherwise the convertor would stay locked up and burn up pretty quick. Think of a manual truck coming to s top without your foot on the clutch.

4) What would a lockup wire connect to if not to a brake switch?
There are many variants of the circuit...see below for a popular circuit layout created with a common relay....but they all should be routed thru the brake switch.....hope this helps

[Rick Bollinger]

In my 68 I used the B&M Lock up kit. You need to use a later model brake switch with cruise control. The second terminals on the switch are always hot until you push on the brakes then it kills the power to the kit and unlocks the converter. The B&M kit is adjustable to lock up at whatever speed you set it at. It is easy to set up. I plan on adding a vacuum switch in the circuit to unlock it during hard acceleration when I get my truck back together.
https://www.summitracing.com/search?...6m%20lock%20up

I see they have gone up in price since I got mine.

[K10-Kansas]

Thanks for the info. I think I've got half a handle on this now. I'll go pick up a different brake switch and look at the wiring and setup and see what's needed.

[K10-Kansas]

Is this the vacuum switch for the lockup?

[Bigdav160]

Could be. The switch should be open with the engine not running.

To add to Aussie's reply. They Superior/Fairbanks make a hydraulic lock up kit that can be used in pre computer controlled 700R4/4L60's. If someone installed one of those you don't need any wiring.

[K10-Kansas]

Ok, so I will do a relay and run it through the brake switch as opposed to going to get a different brake switch.

Do I also connect this to my vacuum switch?

So I should have a TV detent cable, plus lockup relay connected to brake switch plus vacuum switch?

Or is one of those redundant?

[Bigdav160]

The cable on the 700R-4/4L60 is critically important as it controls the pressure. It has to be working properly or the trans will burn out in short order. It's more than just hooking it up to the TH350 kickdown linkage.

[MySons68C20]

I agree with Bigdav....lots of good info here
https://www.bowtieoverdrives.com/

[K10-Kansas]

Originally Posted by Bigdav160

The cable on the 700R-4/4L60 is critically important as it controls the pressure. It has to be working properly or the trans will burn out in short order. It's more than just hooking it up to the TH350 kickdown linkage.

Ok, thanks. Do you know if the vacuum switch replaces the brake switch or do I hook both of those up?

[AussieinNC]

The vacuum switch from GM is non adjustable for delay time, there are aftermarket switches that work with a time delay relay to overcome a possible lugging condition under deceleration.

Most folk delete it or bypass it....

In your case, the wires for the vacuum relay appear to be missing so you should look at using the direct wire relay system or purchase one of the adjustable vacuum systems and go that route. You must use the brake switch, the vacuum switch is optional but if the wires are there they must be able to complete the lockup electrical circuit or it wont work.

Your choice...

On the TV cable subject...it is imperative that the cable be installed correctly, adjusted correctly including the correct angle on the cable attachment points.

[K10-Kansas]

Originally Posted by AussieinNC

The vacuum switch from GM is non adjustable for delay time, there are aftermarket switches that work with a time delay relay to overcome a possible lugging condition under deceleration.

Most folk delete it or bypass it....

In your case, the wires for the vacuum relay appear to be missing so you should look at using the direct wire relay system or purchase one of the adjustable vacuum systems and go that route. You must use the brake switch, the vacuum switch is optional but if the wires are there they must be able to complete the lockup electrical circuit or it wont work.

Your choice...

On the TV cable subject...it is imperative that the cable be installed correctly, adjusted correctly including the correct angle on the cable attachment points.

The TV cable was done by the mechanic that put in the engine and transmission and it all looks good. I'm just trying to finish the replacement of the wiring. I'm 99% done with the complete American Auto Wire classic update.

Ok, I'll definitely get the adjustable vacuum switch. I saw some videos about them and they look like the way to go. So where does the 12v cable from the transmission go? To the vacuum switch or the brake relay? This step isn't in the AAW directions.

I'll also call them Monday and get advice on this step.

[K10-Kansas]

I think this wiring diagram is the answer

[Accelo]

Per the 4th gear question;
Some retrofits have used a hydraulic operated switch, installed into the TC control circuit, to control the lock up circuit. I.E. it will only lock up in overdrive.

Here is a explanation of the process.
https://www.youtube.com/watch?v=DN40gxJeHlE

Lots of methods to skin this cat. Including doing nothing and leaving it disconnected.
Personally I like to see it connected as your cruise rpm will drop by about 200 rpm.
This only applies to the pre-1993 4L60's and/or 700r4's.
Cheers.