Torque Converter Lockup Problem [Archive]

View Full Version : Torque Converter Lockup Problem

07-13-2004, 15:22

I had my 700R4 transmission in my 1990 GMC 6.2L rebuilt again last month. The torque locks up fine around town, but when I get out on the highway and drive 15-20 miles at highway speeds (55-65) it won't lockup after I have to hit the brakes. It has to cool down and then it goes to working again. I can't see it being a heat issue or it would seem that it would also stop working in town after it got up to operating temp.

Can I by-pass the computer by cutting the ground wire for the solenoid from the tranny case and running it straight to ground?

Salemone

07-13-2004, 19:16

Put a pressure gage on the trans. It can be temporary. Use 1/8" copper tubing. the gage should be at least 200lbs.It can be run across the door sill--no holes to be drilled. See what pressures are present when it fails.

07-13-2004, 21:15

Damn, I'd better leave that to the pro's. I thought it might be an easy electrical fix.

I took it to the shop that rebuilt it Tuesday. but as I said it does fine here in town. The tech drove it and it worked every time. He told me to bring it back in when I come back from a short trip and it wasn't locking.

07-14-2004, 20:16

Would being overfilled cause the transmission to give me this problem?

After town only driving and fully warmed the fluid level is about right. I drove it today on a 120 mile round trip and checked it when I got home. I left it idling and the fluid was about 2 inches over full.

Salemone

07-15-2004, 06:46

Indicating overfull should not affect lockup. It does not take much fluid to show 2" on the stick.
I had your same problem--It was pressure related.

07-15-2004, 08:31

Thanks, I'll take it on short round trip and take it back to the shop when it won't lockup as they ask.

07-16-2004, 13:19

I took the truck back to the transmission shop today. He hooked up a diagnostic tool on it.

These were bad
1. Engine RPM sensor
2. Throttle Position sensor
3. EGR sensor???

So he by-passed the computer for the torque lockup. It now starts locking up in 2nd gear. It bogs the engine, but not too bad. At least it works now out on the highway.

Will this hurt anything. I drive the truck more like a car, so I don't do any heavy pulling.