89 760 turbo wagon

[JohnR]

I had a used transmission put into my wagon, and a lock-up was installed. I have read that a lock-up is not normally installed, but this one seems to work alright. However, when cruising along in lock-up state, going about 60+mph, the car seems like it is missing. I know it is not the engine -- and suspect that it is the lock-up torque converter. This only happens in lock-up state. Am I right? Is this 'missing' a sign that the torque converter is about to fail? Or is there an adjustment which can be done? Thanks for the ideas.

[billofdurham]

I have not heard of a 760 box with a lock up torque converter although they are common in later boxes. Who put the lock up in the box?

For other owners I am putting in a brief overview of the lock up torque converter, or Torque Converter Clutch (TCC) as it is properly known.

The TCC is an electronic clutch that will engage the engine and drivetrain 100 percent, something never fully achieved in an auto box without one. It engages usually only in top gear when the car is cruising, not accelerating. The lock up will disengage when the accelerator is pressed hard enough. Over time it will wear out especially if the vehicle ever towed anything and was operated in overdrive (top gear). This will wear the clutch out prematurely. If you have a tachometer you will see the RPM's drop a few hundred when it engages.

If the TCC is bad one of three things will usually happen. First, the vehicle will tend to rev up and down as it engages and disengages, not being able to keep the converter clutch locked up. Second, the converter clutch will engage randomly in gears that it shouldn't even engage in usually. Third the clutch doesn't want to disengage. As you slow down the vehicle won't downshift and if you try to accelerate the RPM's will be so low that the vehicle will have difficulty moving quickly. In extreme cases the lockup converter will try to keep the vehicle moving as you try to stop at a stop light, or will stall out and die.

If you are sure it is not the engine have you checked/changed the transmission fluid. On your model it should be changed every 20,000 miles (32,000 kms).

The other thing you can do is disconnect it. Most TCCs are controlled by a wire or wires that plug into the transmission. It is possible on some models to simply disconnect this plug. This is not a problem and will only cause you to lose a little petrol mileage. The RPM's will run slightly higher than before, in top gear, but will not harm anything or be an issue.

Bill.

[JohnR]

Thank you for the advice -- I will pass it along to my mechanic for his consideration.
Cheers!