What will happen if the TCC isn't wired up?

[BigCountryx]

Just wondering what will happen if the vehicle is driven without having a brake switch hooked up to the TCC? If Pin 33 gets no power, the Converter will remain unlocked as if the brake is depressed all the time if I understand it correctly. What damage will be done to my trans if the TCC wire (Pin33) is not hooked to any power source? What problems should I expect other than potentially running my tranny at a higher temp and hwy gas mileage suffering?

I ask because after installing my new brake switch (from a 96 Camaro) and running it to pin 33 like all the articles say, the converter would not unlock. The switch is working properly, 12 volts to the pcm when not on the brake and zero volts to the pcm when the brake pedal is depressed. After a week of driving, it began to struggle to idle in gear. I unhooked it and now it doesn't die everytime I try to stop. Am I causing any damage driving it with the TCC unhooked? A local guy that has done quite a few LS swaps tells me he never hooks it up, but most of his swaps are for offroad or racing applications.

Specs
1970 C10
2001 5.3
1997 4L80e
Circle D "Performace" converter
2001 PCM and harness

Wiring changes and segment swap for the 4L80 are done and the trans shifts fine with the brake switch disconnected. I'm thinking there may be a short in the plug or wiring at the brake switch that causes voltage to be sent to the pcm when it shouldn't..... But my main question at the top of the post still stands.....

[indymachinist]

Not 100% sure but I believe the end result is trans overheating and damage. I would not do it.

[BigCountryx]

I've got a dual pass cooler on my frame rail. Drove it a total of 1200 miles on the power tour without the tcc wire. I checked the temp of the trans case, pan and the torque converter (Didn't have the cover on it) several times along the way with a temp gun, I never got a temp over 200 degrees even after being in traffic. Granted this isn't a direct temperature of the fluid itself, but it's the best I could do.

[BigCountryx]

Looking at the PSI TCC Brake Switch kit, a note next to the front prongs on the diagram says "Connect to vehicle brake light connector, connect white wire on vehicle to TCC Signal wire". This is the first I hear of this. The only wire I connected was to pin 33 and that was off the rear prongs used for "cruise control". This other connection is noted by the prongs that send signal to the brake lights. What Pin on the pcm should that signal go to?

[BR3W CITY]

Originally Posted by BigCountryx

Looking at the PSI TCC Brake Switch kit, a note next to the front prongs on the diagram says "Connect to vehicle brake light connector, connect white wire on vehicle to TCC Signal wire". This is the first I hear of this.

The harness would have had those wires labeled, didn't you notice 2 wires not being hooked up to anything?

Its the reason that most of us had to switch to the 4-post brake switch, or add a second brake switch. As you already know, thats how the converter knows to unlock if the brakes are depressed.

As for the actual damage that could occur...there are a few things, but none are really a guarantee. As you said, your temps stayed low, so hopefully there isn't gooey-burned trans fluid in the valvebody. Have you taken a closer look at the fluid or the magnet in the pan? Large amounts of metal shavings or carbon will indicate that the friction surfaces have taken heavy wear.

FWIW, I'd actually be more concerned about what happened originally, when it would stall at idle etc. That indicates to me that it was locking up too much, which can actually cause greater damage to the converter. Being fully locked up at very high load an varying rpm can cause internal damage to the veins on the inside of the converter.

My converter actually suffered some similar damage from having a previous tuner (idiot) manually lock out my converter through HP tuners while on the dyno.* The way it was done caused some internal slip in my converter, and the lockup and stall speed never felt the same again afterward.

*While it is doable to do that in certain cases...its more of a diesel thing for the multi plate lockup converters so they build boost and load against the dyno's friction. In my case, it was not good.

[Bigdav160]

The overheating would happen at highway speed (in OD) usually with a load applied (hills, towing, heavy vehicle). It can be so intense that it boils the fluid in the torque converter. After that is when the damage occurs.

[solidaxel]

Interesting!

[Shon]

in all the swaps we have done, the TCC brake switch has never been used. No issues.

[clinebarger]

Originally Posted by Shon

in all the swaps we have done, the TCC brake switch has never been used. No issues.

How does the converter clutch "lock-up" without it? (On gen III stuff anyway)

[Shon]

Originally Posted by clinebarger

How does the converter clutch "lock-up" without it? (On gen III stuff anyway)

Maybe I didn't understand the question.
I was under the impression OP wanted to know about not hooking up the unlock switch when pressing the brake pedal. That's the wiring part that has never been hooked up and every TC has locked up as supposed to per the tune.
We never hooked up the switch b/c even with stock tuning the TC unlocks via the MPH flag in the tune therefore never needed it.

[BigCountryx]

Shon, do you wire 12v to pin 33? My understanding is that without that, the converter will not lock.

[clinebarger]

Originally Posted by BigCountryx

Shon, do you wire 12v to pin 33? My understanding is that without that, the converter will not lock.

Pin 33 of the Blue connector is the correct pin.

If you do not have power on this circuit, The TCC will not lock-up because the PCM thinks your on the brakes. This is a safety feature, If you were to lock-up the rear brakes while the TCC is engaged.....The engine will stall.

[Shon]

Originally Posted by BigCountryx

Shon, do you wire 12v to pin 33? My understanding is that without that, the converter will not lock.

I do not recall specifically making sure that pin has 12v. What pin does that run to on the trans connector?

[BigCountryx]

Originally Posted by Shon

I do not recall specifically making sure that pin has 12v. What pin does that run to on the trans connector?

Pin 33 is fed from the brake switch, not the trans

[Shon]

Originally Posted by BigCountryx

Pin 33 is fed from the brake switch, not the trans

I have never worried with pin 33. TC's have locked and unlocked as tuned in the PCM. Don't know what else to tell ya