A friend recently pulled his his converter - a Yank SS 3200 that he had bought used - and had it restalled. Since getting it back and reinstalling it, the car jerks when settling down to idle speed during braking as it slows down.

If you let the car roll forward at idle, it has the same jerking. When you rev the motor against the brake in drive or reverse, as the revs come down to idle, you can feel it, even though the car's not moving. In neutral, the revs come down smoothly.

No DTC's. We've scanned and even done some tuning, bumping up low rpm spark, editing misfire tables, etc. and no change.

We're stumped.

 

TTT ... can I get some love on this? C'mon - where are you tranny experts?

To put it simply: can this behavior be caused by a TC? If so, please help by explaining.

 

Well barring any other change it would seem it would have to be the converter. Perhaps the lockup clutch grabbing or some issue with the sprag, Though I have never expereinced the symptoms your describing personally.
The fact it does not do it in neutral would seem to eliminat and engine running issue.
A video of it actually doing it might be helpful I dont know.

 

Is there a way of checking if the lockup clutch is grabbing? We have EFILive to work with. Could the clutch be grabbing in first and second gears when it is commanded to be off? He has lock-up in fourth gear only.

This is strictly a low speed issue. The car seems to behave completely normally in all other circumstances.

 

Well I would tend to agree, if the converter is the only thing that has changed then that kind of points the finger at the converter right there and not tuning.

 

sounds like a leak in the front pump halfs and fliud bypassing into the converter lockup oil flow path.
the converter clutch cannot come on without a fluid flow change as the normal oil flow is to release the converter clutch.
the converter has no sprag but a roller clutch is not the cause and will not act as stated.