Tow truck tranny issues, back again

[BTR69]

Originally Posted by Alan Roehrich

Why was it rebuilt to begin with?


Those are pretty reliable, I don't seem to have too much trouble with them. But then they get the Sonnax fixes, the Alto frictions, and a Superior valve body kit. That tends to eliminate further problems.


Order yourself the ATSG manual for the 4L80E. If you're going to work on it, you'll find that to be indispensable.

After swapping out several parts that "could" cause it to go through 1-2 shift, then on 2-3 shift, it still falls back to low gear. Tranny shop I took it to has taken good care of me in the past and has a great reputation around here. The only thing left that they came up with was a rebuild. They did find a couple of internal issues that would end up causing me more grief and fixed those. I remember one having to do with a part that had been machined with too much tolerance from a prior rebuild. I'm taking their word on that. I know they upgraded it with the Sonnax parts. They kept it for a while troubleshooting and feel the ECU may be the problem. If I can find one in the junkyard, I may grab it, but have been told I'll likely need it flashed. The only other things that I can think of that haven't been changed out are the input speed sensor and neutral safety switch. Unless they did those and I'm not aware of it. Swapping those out tomorrow. If it doesn't work out, I'll look into the stand alone tranny controller. Looked them up this evening and seems like a viable option.