Torque Converter lock-up Disconnect

[RocketScience]

The torque converter lock-up feature (E40D) in my '90 FS Bronco is starting to go, causing "shudder" at certain speeds.

Word has it that you can disconnect this lock-up feature at the tranny wiring harness. Anybody know how to do this?

Note:
This rig is not a 'daily driver', so I'm not concerned about the fuel mileage loss by this "bandaid" fix.

 

[Skandocious]

You need to tap the purple with yellow tracer wire from the transmission harness on your driverside wheel well. Here's a good tutorial:

http://www.forgotton.net/mods/tclock/index.htm


The best way to do it is to use a 3-position switch, so that you can have:
-TCC Forced Lock
-TCC Forced Unlock
-TCC Automatic (stock)

 

[Skandocious]

Here's some more info:

http://www.dieselinnovations.com/techfiles/tclockup.pdf

It just locks the TCC when you apply a ground to that purple/yellow wire on the transmission harness. If you want to use just a simple 2-position switch to lock it, all you have to do is use a wire tap on the purple/yellow wire, then apply a ground to one end of the switch and run the other end to that purple/yellow wire.

I know a bit about this cuz it's a mod I plan on doing soon

 

[RocketScience]

Wow, thanks for all the great info, Chris.

Actually, all I want to do is a "forced unlock", and leave it that way. What would be the simplest way to achieve this?


Rob

 

[Skandocious]

Oh... Well at which speeds are you getting this shudder? Because generally the TCC doesn't lock up until you get into overdrive (although it can lock in lower gears depending on speed/RPMs/engine temp). I would bet that your shudder is something else but if you'd like to test it you could just snip the purple/yellow-tracer wire that I mentioned before.

Basically all thats happened is this...

```````````````````````````````````````````
| Computer |------------------------|Transmission|
```````````^^Purple/yellow wire^^`````````````


The TCC is UNLOCKED most of the time when you're driving below about 40mph. Once you hit the point for the TCC to lock, the computer just sends GROUND to that purple/yellow wire, and that ground tells the solenoid in the transmission to lock the TCC. As long as the wire doesn't get ground, the solenoid won't get the signal and the TCC will never lock.

The easiest solution would be to just snip and cap the purple/yellow wire if you just wanna test it and see if the TCC is your problem. If it isn't splice the wire back together. If it IS, then you could wire a switch between the two wire ends which would break the circuit and keep the TCC unlocked as soon as you flip the switch in the cab.

Lemme know if that does or doesn't make sense. Good luck

 

[RocketScience]

It all makes sense, and I'm positive it's the TC as I did the 'tap the brakes while shuddering' test per a friend of a friend who is a tranny guy.

I'll try this and see what happens:

....The easiest solution would be to just snip and cap the purple/yellow wire if you just wanna test it and see if the TCC is your problem. If it isn't splice the wire back together....

 

[Skandocious]

Oh well then great! It's always nice to have a positive diagnosis on a truck problem Good luck and keep us posted.

I should also warn you that this might adversely affect your mileage at speeds above about 40mph, as well as probably causing your transmission run a bit hotter.

 

[RocketScience]

Oh well then great! It's always nice to have a positive diagnosis on a truck problem ...

Hahaha.....

I guess I should have mentioned that many of the other things that may have caused the shuddering were trouble shot prior to the 'tap the brake...' test (u-joints, mounts, suspension, etc.). So again, I'm pretty sure (well, 97.6%), that it's the TC.

 

[Late Model Man]

I know this thread is pretty old but there are dangers associated with this.

You need to be very careful when eliminating the TC lock on the E4OD because the TC slipping generates heat, LOTS of it. As I'm sure you have heard, our old faithful E4's are not quite known for running cool. You need to watch trans temp intently when crusing, towing etc, anywhere really. Otherwise you risk fluid breakdown and toasting your expensive tranny. I'd fix the TC clutch or just live with it.