700R4 TCC Wiring
 

EDIT: I ended up developing an Arduino-based controller after struggling with the limitations of a vacuum-switch-based setup. Arduino development starts on post #47.

I rebuilt a 700R4 and installed it in my truck recently. I spent a decent amount of time researching how to wire the torque converter clutch (TCC). The methods I found range from installing a manual toggle switch to buying a full blown kit from various companies. I decided to take the middle of the road and use a vacuum switch and a time delay relay. Here are the characteristics I wanted in my system:

1) The TCC locks automatically in 4th gear only

2) A vacuum switch unlocks the TCC when vacuum drops due to acceleration

3) The TCC unlocks when the brake pedal is pushed

4) When all conditions are met for locking the TCC (4th gear, high vacuum, brake not pressed), the TCC will be locked after a delay of 8 seconds

The delay relay is required to prevent hunting, where the TCC is locked and unlocked repeatedly when the vacuum level is on the edge of what is required to lock the TCC. I did experience this issue on my first attempt at wiring the system without a time delay relay. I also tried installing a vacuum delay valve, but the vacuum switch is designed with a small leak which prevents the vacuum delay valve from working properly.

There is a subtle difference between how I wired the relay and how it's usually done. Most examples I found had the relay trigger negative terminal connected directly to ground, and they had a jumper between pins B and D of the transmission connector to hard-wire the 3-4 switch to the TCC. The problem I see with this approach is that it allows the TCC to lock up simultaneously with the shift from 3rd to 4th during mellow acceleration. I wanted the relay to delay TCC lock up until eight seconds after shifting into 4th during mellow acceleration. I achieved this by using the 3-4 switch to provide ground to the relay trigger negative terminal. This approach has two benefits:

1) The shift from 3rd to 4th+TCC during mellow acceleration is too radical of an up-shift, and causes the engine to strain. Delaying TCC in this scenario allows engine RPM to increase a little bit more before locking the TCC

2) Engine strain resulting from 3rd to 4th+TCC is usually responded to by pressing down on the accelerator a bit. Depending on the acceleration rate, this can deactivate the vacuum switch, causing the TCC to unlock immediately after it had just locked. This doesn't feel smooth

Here are the parts I used:

GM 25524845 Brake Switch
TCI CMP3766B Vacuum Switch
HELLA 996152151 Delay On Relay
MUYI 5xSKU20909-MY Relay Socket (ordered on Amazon)
American Autowire 500323 Plug for 700R4
Dorman 18g wire in orange, pink, red, white and black
Packard 56 male & female crimp sockets for bulkhead connector (eBay)

My transmission is a model year 1993, so it already had a normally open 3-4 switch. Some older versions of the 700R4 have a normally closed 3-4 switch. If this is the case, then the switch has to be replaced.

I wanted the wiring to look reasonably stock. Here are some things I did to achieve that goal:

1) I tapped into fused 12V on the orange wire that is on the stock brake switch. I found a stock connector in an early '80s van for the second set of contacts on the brake switch, and connected one of its terminals to the stock orange wire

2) I was able to slip the pink wire from the new brake switch connector through the existing plastic wrap on the harness that contains the stock brake switch wires

3) I used an empty slot in the bulkhead connector to route the pink wire through the firewall

4) I wrapped the pink wire inside the harness that runs over to the distributor

5) I used original style plastic wrap on the wires that run to the transmission

6) I secured the transmission wires in the same firewall clips that hold the brake light wires

Re: 700R4 TCC Wiring
 

Here are some photos of the brake switch wiring

Re: 700R4 TCC Wiring
 

Here are some photos of the transmission and relay wiring

Re: 700R4 TCC Wiring
 

Here are the relay and vacuum switch mounted to the intake manifold

Re: 700R4 TCC Wiring
 

I think you chose the best way!

Re: 700R4 TCC Wiring
 

Nice job

Re: 700R4 TCC Wiring
 

The relay should be pointed down. In the unlikely even that it should see water the relay and the connector could get wet. With it turned over any water would run away from the relay.

Re: 700R4 TCC Wiring
 

I set mine up exactly the same way. Only difference is the time delay of 10 seconds instead of 8. Works fairly well

Re: 700R4 TCC Wiring
 

Yeah, you're right, and that occurred to me, but things are pretty cramped back there. I'm going to have to revisit this. I'm thinking sideways would be better than pointing down because the end that is currently pointing down has dip switches and a potentiometer on it, and it looks like water might be able to get in that way.

Re: 700R4 TCC Wiring
 

Your system install looks exactly like something GM would have done.
Very nice job on the install. I have seen many an 700R4 retrofit without and of the lock up wiring connected. Nice job utilizing all the tech built into the transmission.
Rick

Re: 700R4 TCC Wiring
 

Thank you! I would have preferred to go with the vacuum switch and vacuum delay valve installed originally with these transmissions, but they aren't available anymore. I did manage to find a switch and valve in a wrecking yard, but they were no longer functional.

Re: 700R4 TCC Wiring
 

The nice thing is that it is very easy to adjust.

Re: 700R4 TCC Wiring
 

There are two limitations I'm seeing with my current setup:

1) If I'm driving down the highway in 4th gear and with the TCC locked, and I lift my foot off the accelerator to coast, the TCC unlocks since the vacuum switch is connected to the timed vacuum port on the carb. This is good because coasting is more fuel efficient than engine braking. The issue is when I reapply the accelerator, I have to wait unnecessarily for eight seconds for the TCC to lock up again. During this period of eight seconds, I have to press down farther on the gas pedal than I was before coasting because the engine has to spin up to a higher RPM. Then, when the TCC re-locks after eight seconds, I have to let back off the accelerator. One possible solution would be to connect the current vacuum switch to manifold vacuum, and then add a second vacuum switch connected to timed vacuum that cuts off 12V to the TCC upstream of the delay relay. This would allow the TCC to re-lock immediately after resuming from coasting.

2) If I am driving at a moderately slow speed (~40MPH) up a hill, the TCC will lock, putting too much strain on the engine at a low RPM, causing the need to press down on the accelerator. This causes the TCC to unlock, resulting in undesired acceleration. These two scenarios come and go every 8 seconds, or until the hill ends. A possible solution for this might be to add an RPM-controlled switch to the circuit that requires the RPM to be over something like 3000 before the TCC is allowed to be engaged. The RPM-controlled switch would need to have an off trip point at a lower RPM than the on trip point so that it wouldn't immediately unlock the TCC due the the RPM drop that results from locking the TCC. The MSD 8969 RPM-Activated Window Switch might work this way. The $200 price tag is painful though.

I may just try connecting my vacuum switch to manifold vacuum to see if having engine braking when coasting is more tolerable than the delayed TCC lockup after resuming from coasting.

Increasing the time delay of the relay may help reduce the annoyance of repeated locking and unlocking on a hill at lower speed.

Re: 700R4 TCC Wiring
 

Have you considered using slightly lighter weight, in the governor, to delay the shift somewhat?

It is easy to see why this was such an issue before they went to full electronic controls. Personally locking up the converter and shifting to forth gear at the same time is tolerable to me. You are taking the drivability to the next level.
Rick

Re: 700R4 TCC Wiring
 

Lightening the governor weights is an interesting idea. I'll have to think about that when I'm driving around. It's the TCC lockup that I'd really like to delay, but delaying 4th would kind of do the same thing. My WOT shifts are happening at around 5500 RPM right now, and I don't want that to go any higher.

My transmission setup is really working quite well right now. I'm just nitpicking. I imagine GM had all of these little quirks worked out when they went to an electronic speed sensor and an ECM on the early fuel injected vehicles. I haven't ever driven a vehicle that came stock with a 700R4.

Re: 700R4 TCC Wiring
 

The way mine is set up the vac switch is hooked to manifold vacuum. When I go into a cruise condition in 4th the converter Locks after 10 sec. I set the vac switch at about 8" of vac. So it only unlocks when vac drops below 8". slight grads it stays locked, but heavy pulling will drop it below 8" of vac and unlock. My only issue is I have a 2004r and it shifts way too early in light throttle driving, so I mostly drive around town in D as even with 4.10 gearing 30 in OD lugs the engine more than I like.

Re: 700R4 TCC Wiring
 

i went down this road too. After I tried multiple ways I finally settled on a toggle switch under the dash. When I am in the city it is off when I get on the highway I turn it on. This works well for me.

Re: 700R4 TCC Wiring
 

I will give manifold vacuum a try. My switch trips at 6", and it isn't Adjustable. I will also increase the time delay.

Edit: My switch is in fact adjustable. I didn't notice the tiny set screw in the middle of the switch initially.

Re: 700R4 TCC Wiring
 

A toggle switch sounds nice and straightforward. I suppose it could be added to my existing system.

Re: 700R4 TCC Wiring
 

I'm totally ignorant about automatic transmissions but I recently bought a ('86) 2004R for my next project due to a bad left knee. Will this same set up work for a 2004R?

Re: 700R4 TCC Wiring
 

Since space is a challenge for you, the water/weather proof relay's work well:
https://www.summitracing.com/parts/p...SABEgIyYvD_BwE

I use them on the front of my truck for all my lighting harnesses, they are exposed to debris, water, moisture, wind, heat, etc. and work flawlessly.

Re: 700R4 TCC Wiring
 

Those look very nice

Re: 700R4 TCC Wiring
 

I moved my vacuum hose over to the manifold, and now the TCC doesn't unlock when coasting. I like this much better than having the TCC re-lock eight seconds after every time I coast. I was finding myself trying not to coast so that the TCC wouldn't unlock. That's just dumb. Anyway, engine braking will be good when going down steep mountain passes.

Re: 700R4 TCC Wiring
 

I'm not at all familiar with 2004R transmissions, but this document implies the wiring is the same as the 700R4. You will have to figure out whether the 4th gear switch inside your transmission is normally open or normally closed (it needs to be normally open).

https://www.jegs.com/InstallationIns...890-376600.pdf

Re: 700R4 TCC Wiring
 

Yes exactly the same for 2004r and 7004r. you will need to use a 4th gear pressure switch normally open. When you enter 4th then it will close grounding the solenoid. the most simple setup is to run a wire from the + side of the TCC solenoid to power thru a switch. Once your in 4th, flip the switch feeding +12v to the TCC solenoid and it will lock, when the trans downshifts to 3rd or lower, the pressure switch opens and you no longer have ground to the solenoid thereby unlocking the converter.