Torque Convertor Unlocking?

Craig482 · August 9, 2011

My truck is a 2001 gmc 2500hd 6.0l. The problem I am having is that at highway speeds (70-75) it unlocks the torque convertor and the rpms rise to about 2800-3000. I have changed the electrical harness on the transmission but still have the problem. I'm not sure if its related but the transmission temp guage starts going crazy when the torque convertor unlocks. Any advice???

wavery · August 9, 2011

My truck is a 2001 gmc 2500hd 6.0l. The problem I am having is that at highway speeds (70-75) it unlocks the torque convertor and the rpms rise to about 2800-3000. I have changed the electrical harness on the transmission but still have the problem. I'm not sure if its related but the transmission temp guage starts going crazy when the torque convertor unlocks. Any advice???

What is the normal RPM at 75?

What rear-end ratio do you have?

When you say, "the transmission temp guage starts going crazy", what does that mean, in numbers?

I have a 3.23 ratio and my normal RPM @ 75 is about 1800. 2800-3000 on my truck would be huge and something would be seriously wrong. If you have 4:11 gears, that's a whole different scenario.

Craig482 · August 10, 2011

It normally will run around 2000-2200rpms at 75. It has 4.11 gears. The transmission temp gauge will start to go up and down rapidly. It will go from 150 to zero then jump again. It won't stay consistent until the torque convertor locks again. Sometimes if I slow to 55 it will lock back up but as soon as I accelerate back up to 70-75 it will maybe stay locked up for a couple minutes then unlock. I have heard of a number of causes from bad o2's, tps, to bad line pressure. I have seen a couple of posts here on this similar problem but no real definitive answers.

wavery · August 10, 2011

It sounds to me like you may be low on fluid or the filter has dropped off or you have a plugged filter. It sounds like you may be getting air in the pump........ That's not good....... I wouldn't drive the vehicle like that.

When the temp shoots up, it may be sucking air and there may be no fluid around the sensor.

Have you checked the trans fluid (with the engine idling)?

If so, what color is the fluid?