700R4 torque converter won't lock up

[Dignan]

I have a 1991 Ford Explorer XLT 4x4. The A4LD was replaced with a 700R4 about 30k miles ago. I had it serviced a month or two ago and the guy said it looked great inside. It runs great and shifts fine, but recently the torque converter stopped locking up. I checked voltage at the tranny and I'm getting 11.9v. I get a constant voltage with key on. Should it be 0v then switch to 12v when its time to lockup or is it supposed to be constant? If that is correct then any other ideas?

Thanks

 

[Maniak]

When there is 12v to the trans it is being told to lockup. That is why you use a relay to break the 12v gong to the trans when you hit the brake.

You need to find where the were the 12v is coming from.

follow the wire with 12v back up and find the relay/switch that its connected to. My SWAG is that the relay that is used to turn off the relay is broken OR the relay isn't seeing the 12v from the brake switch so its not opening the connection to remove 12v from the trans.

~Mark

Edit:

It just occurred to me, I believe there are 2 wires that can go into the trans to lockup the converter. One gets constant 12v and is used to automatically lock the converter when you hit 4th gear. The 2nd wire is used to tell it that it can lockup in other gears. It will actually lock in any gear except first. If I can find my notes from when we installed the trans I'll post what I used for my wiring..

EDIT2:
I found bowties diagram. The top one just shows how to get it to lockup in 4th automatically. The bottom one show the extra connection so you can tell it to lockup in 2 and 3.

http://www.700r4.com/tech/tcc/relay_install/diagram.shtml

 

[Dignan]

Thanks for the diagram. That will be a big help. I'll trace it back to the relay and check that.

 

[Dignan]

Question about the diagram. Is there always the blue line inside the transmission? I have the setup like the first picture with just a red lead going to the transmission. I would like to add the switch to be able to lock it up in 3rd if I'm not in OD, but I don't want to go through the hassle of running that blue line on the outside unless it will have the blue line inside. Does that harness pop out to check?

 

[Maniak]

Every 700r4 Ive seen has the wires "in" the trans. Ive seen a few "kits" that did not have the conductor on the external wire/plug harness.

~Mark

 

[Dignan]

My kit does not have the external wires, but that can be added easily enough.

So based on the diagram, the brakes are connected to 85. So if I hit the brakes, that should send power to 85 which will interrupt the connection between 87a and 30 which will disengage the torque converter, right? I'm not sure I got this right, but it looks like the tranny will always get 12v unless you are pressing the brakes. Is that right?

I tested the voltage around the relay. I am getting a constant 12v from the wire hooked to 85 even without hitting the brakes. That would explain why I am not getting the lockup because the relay constantly thinks I am braking, but that still confuses me because I'm getting 12v at the tranny.

 

[Maniak]

With 12v at the transmission, it should be locking up in 4th gear Assuming you have the kit in there that will automatically lock it up once in 4th. As I understand it, it just controls the 4th gear oem solenoid.

So, if you have 12v going "to" the transmission then either the converter is broken and won't lockup, the lockup solenoid is bad or you have a issue with the lockup "kit" that is installed in the pan.

Next step will be to drop the pan and see if that 12v make it "into" the trans and all the way to the lockup solenoid. If it does, your down to the solenoid or the converter itself.

But... back to your last post....

If you getting 12v at pin 85 (and assuming 86 is ground) then it does indeed think your hitting the brakes. You have a short somewhere or there is more to your circuit than the single relay.

With power on pin 85, pin 87a should not have 12v since 87a is the normally closed switch which will open when power is put to pin 85). Pin 30 is the switched power that is interupted when pin 85 gets power...

So, What you said your seeing doesn't make sense. If power is on pin 85, there should not be power on pin 87a which means there should not be power at the trans. On top of that.. If you do have 12v going into the trans then the transmission should be locking up. We must be missing something here since those two things (power on pin 85 and power at the trans) are mutually exclusive.

~Mark

 

[Dignan]

Well at least the part that was confusing me is confusing you too, so that means I'm not stupid. I'll go test some more and see if I can figure something out that makes more sense.

 

[Dignan]

I may have found part of the problem... the line going down to the transmission was attached to 87 not 87a. That would explain why it still got voltage while the brake line was sending voltage to the relay. I guess with the constant 12v at 85 and the transmission being fed from 87, i had a constant 12v at the transmission 100% of the time. So now I don't have 12v at the transmission and if I can attach the 85 line to a source with 12v only when braking I'll be setup correctly and then we'll see if it works.

 

[Dignan]

I cut the voltage from the brakes. I didn't find a switched power source right off so I threw a switch in there so I can connect it when I need to stop. Kind of a bandaid until I get the brake source hooked up correctly, but I'm out of time for now.

 

[Dignan]

I drove around with it not getting 12v. Still no lock up. Any other ideas or is it just something internal?

 

[Maniak]

You drive with 12v not going where?

The trans needs 12v @ the trans to go into lockup..

You use the relay to take the 12v from the brake light and use it to stop the 12v at the trans while the brakes are applied. That turns off the lockup while the brakes are on.

If you just put 12v at the trans (temporary) and drive it, once you reach 4th gear the converter should lockup. If it doesn't you have an issue with the converter the 4th gear lockup solenoid or lockup kit issue (wire etc).

~Mark

 

[Dignan]

Sorry for the confusing post. I meant no 12v going to the relay so that it wouldn't switch off the 12v supply that the tranny had. I decided that it wasn't wiring, so I just made sure it was wired just like the diagram and put it all back together to deal with another day. I drove around for a couple of days with no lockup. Then, all of the sudden, it locked up. I don't know how or why. It was pretty picky about what RPMs or speeds it would lock up, I had to let it shift into 4th at 37mph and then let off the gas at 43mph and it would lock up. Then after about a week of that, it started being less picky and locking at more various speeds. Now, it locks like it supposed to. Any speed over 40 and it will lock if I let off the gas. If I don't let off by 55 or so, it locks without me letting off the gas.

I don't think I really did anything to it, it just decided to start working again.