Question: TCC Problem

[Tim81]

I have a couple of questions regarding the TCC operation in our cars. First my converter locks up right after the trans shifts into 3rd, sometimes I'm only going 35 mph or so. Is this normal and can it be adjusted any at all? Second, sometimes when I'm cruising at highway speeds 65 or 70, the converter lock out will rapidly toggle between locked and unlocked, it will be locked for a few seconds and then unlock for a few second and keep repeating this cycle with my foot on the accelerator the whole time. I've noticed the second problem more on cooler days, temps in the 40 to 50 range. I have not troubleshot the problem yet, just wondering if anyone had any suggestions..........Thanks Tim

 

[TimAT]

I don't recall exactly how they did that TCC thing as far as control circuits- been a long time-

Drive it and when it starts the lock/unlock thing, just touch the brakes- not enough to really apply the brakes, just turn the stoplights on. That should force the "unlock" and you can double check that it is being controlled.

I'll do some digging and see what I have on the 350C trans- I'm going to guess that the solenoid is what the problem is- if it's leaking or losing it's holding power that could cause your problem. If you need to raise where the TCC locks- (IMHO, it should not lock until about 40-45) you can get a pressure switch - oddly enough, the 3rd gear switch and the pressure port it's in are just about an even PSI/MPH. 40PSI=40MPH. Not exact, but really close.

 

[Tim81]

Thanks Tim,

I have a pretty good understanding how the system works and I agree with what you are saying. Are the 3rd gear switch and the pressure switch the same-thing or would I substitute the pressure switch for the third gear switch? Once the weather gets better (no snow on the ground) I was thinking about rigging up a switch that would keep the trans in lock-up and see if I still have the problem. I hadn't thought about the solenoid going bad thanks for the input.......Tim

 

[22229stingray81]

Tim,

Your TCC lockup appears to be operating normally. Yes, it's normal for the lockup to go on shorty after getting into 3rd gear. And mine also jumps out and in while crusing on the highway. What many people do is install a toggle switch in their cockpit to manually lock and unlock it, because it can get annoying. Even if everything is working perfectly it is still an annoyance. Sorry, I can't answer any questions about adjustments. Hope this helps.

-Tatortot

 

[Tim81]

Tatertot,

Well I guess it is good to hear that my car is normal, it does drive me crazy so I'm going to install the switch. I read that its easy to install. How could GM figure that people would be happy with this design? Go Figure

Tim

 

[TimAT]

The 3rd gear switch/pressure switch are the same. Pull it out and hook it up to air and see where it closes. GM used to have several different switches that all came in at a different pressures. Find one that's 5 PSI more and try that.

 

[Sensei]

I answered your PM with how the system works and how I would proceed, but I did not mention how to install a manual switch. Just put a SPST mini switch (Radio Shack) in the power wire going to the brake pedal switch (where you would connect the constant 12V if the computer is giving intermittent current). The wire runs under your console so the switch can be put in a number of convenient places. It will allow you to turn the 12V off so the TCC does not lock up.

God bless, Sensei

 

[GerryLP]

I do not have that problem with my TH-350C. A few years ago I did have a weak seal between the solenoid and the valve-body orifice plate, and it would cause a lag while shifting that it almost emulated a manual transmission when shifted at low vehicle speed/low engine speed. You have received some good inputs, and I am just adding to them.

If you decide to replace the solenoid, take a very good picture of the transmission wiring at the valve-body. The different wiring options in the shop manual did not match the one for my Vette's transmission. The replacement solenoids do not come will all the wires (not anymore) that the Vette TH-350C's came with. You'll have to reuse or manufacture a new wiring for the new solenoid (it basically wires the pressure switches in parallel and in sequence) to cover certain driving situations, I guess.

You might want to consider adding a drain plug to the pan, so that next time you won't make such a mess on your garage's floor.

Also, does your vette has the original speedometer? If so, then it should include the Vehicle Speed Sensor (VSS) on the back of it. If it was replaced for a 140 or even a 160 MPH speedo, then it could be that the one the previous owner put on did not have the VSS window to attach the sensor...the VSS plays a part with TCC...just little ideas where to look.

GerryLP:cool

 

[larryg3]

ok foolish question, how do you know when the converter locks out??? i have not felt any difference when I am driving my car!!

 

[TimAT]

Drive on the highway at 55, 60 and hold a steady pressure on the gas. Gently touch the brake- just enough to turn the brake lights on. You should feel the TC "unlock" and then lock when you take your foot off the brake. IF not, it's not working. Quick and dirty test.

 

[GerryLP]

The L81 was also special in which that the computer would send a signal to lock the tq converter when shifting from first to second and second to third.

One quick and dirty way of telling is when the tach needles slams to a particular engine speed, and if you give it some gas (not slamming the gas pedal), you'll notice that the engine RPM needle will not move higher or faster relative to the speed the vette is traveling. When fluid coupling is the only condition between the engine and the transmission, you will notice upwards of 200 more RPM's on the Gage when giving it gas, and the movement of the needle will follow the gas pedal (for example, give it gas, rpm increases, take away gas, rpm decreases).

 

[larryg3]

ok i will check it out next time i go on a cruise. thanks