4L80E, unexplainable code 68 and weird 4-3 shift.
Hopefully someone can help me out here..
I have a -93 Suburban 5.7L with 4L80E. There have been some trouble with the tranny since I've bought it 6 months ago. But haven't found time to check it out until now. It had code 68, and no 4th gear. decided to take down the pan and install a shift kit, and go trough the valve body. (The man I bought it from told me the tranny was rebuild like 2000miles ago, but the warranty was out cause he had not been using the truck the last year.) I soon realized this rebuild was done by someone who had never seen the inside of a tranny before, when I dropped the pan. So I pulled the tranny out right away, so I could do the rebuild properly my self. ( the tranny was not inline with the engine, broken 4th clutch suply bolt, loose center-support bolt, generally over tightened bolts +++) So I did a proper rebuild on it, installed the shift kit, new internal wiring hardness. reused all solenoids, changed input speed sensor cause of a leak trough the sensor itself in the old one, new converter, and of course all seals, clutches etc. Then I put it back in the truck, and took it for a test run.
I experienced a delayed delayed 2-3 shift and a to early 3-2 shift (ECM comands it that way). I but can live with that.
To my big problem: have been using it for a few days now constantly monitoring it with my scan tool. sometimes it sets code 68 and shifts down from 4th to stay in 3rd until i clear the code. when clearing the code while driving it shifts right back up and can stay that way all day, or it can set the code again after a few miles. the code is set and then it goes about 2 seconds before it downshifts. I don't notice any slip, TCC is applied and seems to be holding fine when it sets the code. any ideas what can cause this? faulty ECM??
Another thing started today, sometimes when downshifting from 4th to 3rd (kickdown only, both partial and WOT) it appears to go in neutral until I let off the throttle a little. then it engages 3rd. no code is sett. have tried to hold it rewed up when it frees out in the shift to force it to sett a code held it there for about 10 seconds, still no code. no burned oil, so I've concluded with that it's not slipping just no engage at all. cause I've tried to burn oil and clutches, just to make a visible fault in the tranny in case I had to open it again. (ECM is commanding 3rd)
I have one theory that I hope is wrong.. valves sticking in valve body when it's tightened to the case. Caused by earlier over tightened vb bolts. I'd be glad for any thoughts you might have on this issue or any other theory you might have. Considering to get a used tranny to rebuild, but I'm usually not the kind that gives up on a tranny.
For the record, I have rebuilt approximately 50 of these transmissions without any problems, and now this.. I'm glad it's in my own truck and not a tranny for a customer...
