I have a '75 Suburban with a 350 tranny, and I noticed a brown wire that comes from the transmission area that is not hooked up to anything. It runs by itself, not in a harness, and almost makes the fuse block but is about a foot short.

Is this a TCC lockup wire? I've had a TH200 in a Camaro that I could toggle the TCC, and I would like to do it again. Does the 350 have TCC?

It does not lock up now, just 3 straight gears.

Thanks all!

Id say yes. But I dont think they came out with the lockup till the early 80s. Probably your trans has been swaped out at one point in its life with a later one. Wire it up and find out...

Yeah, it looks swapped, or at least rebuilt.

I think it could be a tach wire maybe? I have no tach, but I guess you are right...just put it on a switch and ride to find out. I think I will throw an inline fuse in there...it's my daily driver...:shocked:

Thanks!

There should be a plug capable of 4 wires total just above the shift lever. The purple wire is power from the brake switch, and I believe light blue is high gear lockup. Some Camaro's had another wire that would lockup in second gear too. Mine works great, and my TPI locks it up.

This wire is definitely brown...or a medium tan? I haven't inspected the shift lever area, I just noticed that it had this wire and remembered the Camaro. I used a switch on the OBD-I port on the Camaro...this one just has this mystery wire...?

Would I just hook it to a switch going to ground, and ground it to lock up? Or apply current for lockup? I am a bit dubious about putting power to it unless I am sure.

I I noticed a brown wire that comes from the transmission area that is not hooked up to anything. l!

I think it could be a tach wire maybe? I have no tach,!

well does it come off the tranny or not? the "transmission area" is a pretty shitty description.

wtf would a tach wire be doing in the "transmission area"?


the fuel tank gauge wire is brown and in the "transmission area"

I highly doubt it is a lockup or tach wire. 1975 should not even have an HEI distributor on it. If it did the tach comes from there. No lockup in trucks that year either. I have a 76 with a 350 turbo trans in it, if it is not raining bad later on today I'll look at it and see if I can trace it out.

th350-c. I used to have one in my landcruiser (not stock obvisoulsy). Mine was controlled by a foot pedal switch near the brake. Worked great. There should be a small lead off the the tranny on the driverside for idenification. You would have to have the ecm re-programmed (unless the ecm was programmed for it originally) to have the lock-up function work without a manual switch like I had. It does make a difference in MPGs on the highway and also helps with heat control.

OK, I stand corrected, HEI started in 1975 so you should have an HEI distributor, again a tach would come from the tach lead on the distributor.

There is a wire on 350 and 400's that is for the torque converter clutch solenoid. it is just ahead of where the speedometer cable comes out of a 2wd transmission on the drivers side of the transmission. Look at that and see if that is the wire you are seeing.

I do not remember my 76 having a lock up converter.

On the body wiring diagram the brown wires are running lights, it should be in a 4 wire loom that runs down between the steering column and chassis.

I'll keep looking for more info on the wiring loom, when I find it I'll post what I found.

I believe the first year for the TH-350C was 1981, and started with Camaro's. They had three wires, and were capable of lockup in 2nd & 3rd. They were later used in other models and lockup was done through a vacuum device.

Around 1980 a lockup torque converter was introduced; this transmission was phased out in 1984 in GM passenger cars for the 700R4. Chevrolet/GMC trucks and vans used the THM350-C until 1986. The lockup torque converter was deemed unpopular with transmission builders - B&M Racing once marketed a conversion kit for THM350-Cs during the early 1980s until the advent of high-stall lockup torque converters when its overdrive counterpart (THM700R4/4L60) were modified. The standard TH350 is still very popular in drag racing.

Built for serious performance, this is a great converter for moderately modified street machines and weekend race cars that are also used as daily drivers. It provides approximately 2400 to 2600 rpm flash stall without negatively affecting part throttle driving, so is efficient at highway cruising speeds. Yet it also launches hard at wide open throttle. On average, it will multiply torque by 2 to 1.
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Excellent! That was the information I needed, thank you, just4cuz. And all others with valuable info.

I had a Camaro like you are talking about, a 1982 with a TH200C. It had the same setup as what you describe: lockup in second and third by vac switch. I set up a toggle switch on the Camaro's OBD port and it would drop the RPM at cruise significantly.

I don't know where the 200C sits in terms of strength, but they used it on Chevettes AND Buick Grand Nationals? Weird.

If I find that the transmission I have (TH350) has the leads (which are not hooked up) then I will be very pleased. I assume that the "C" means Clutch, or Converter?

(and I knew better than to think it was the tach wire. Dunno why I asked that.)

This 75 is getting better by the day. Can't want to take it out.

you assume correctly.

GM th350s from 80 on have a TCC setup, the valve body is different, and while they can be changed to not have a TC clutch wiring setup to a regular th350, you wont gain much if anything. easy way to tell is to wrap your fingers around the drivers side rear of the case and see if you can feel anything on the flat spot above and behind the shifter shaft, about 3 inches from the rear of the case, about an inch in. If you dont have a plug there, you have a regular th350.

the 200c is comparable in strength to the 700r4 that replaced it, which was used behind 2.8 v6s all the way to 5.7 v8s, and after a bunch of updates, is in use today as what they call the 4l60e/4l65e. still not worth the aluminum it was cast from, in my opinion.

but hey.. at least you dont have one.

the brown wire could be emission related.Some of the early 70`s trucks had a thermo vacuum switch that limited vacuum to the vacuum advance unless the temp was high enough at the switch.

They also had an electrical switch that would allow full vacuum if the pressure switch on tranny was grounded by being in high gear.Drive in your case.

Brown wire is 2nd gear lockup, blue is high gear, and purple is power source.

Pull the pan and see if the wire goes to a solinoid. I cant think of any other reason for a solinoid to be on the valve body except for TCC lockup

why not check to see if it even has a lockup wire?

Im willing to bet its not a lockup unit.