6L80 Transmission 4-5 Very Hard Shift

[remix919]

I got a new to me truck with the 6L80 transmission, runs great except has a VERY hard shift from 4-5, I'm a BMW tech so familiar with mechanics in general but don't have much knowledge on the 6L80. I already dropped the valve body and rebuilt the seals with the sonnax kit but unfortunately that didn't help at all. I don't think the actual clutches are bad because usually when the clutches are bad the tranny will slip, hard shifting is typically an issue with pressure. I also got the codes P0842 and P0877 for transmission fluid pressure circuit low voltage for switch 1 and 4. Any idea what the cause of the issue is or where to look?

[dna9656]

What I can tell you about the tranny: GM is in court all over the country over this tranny. GM found a way to make a torque converter less expensively; they use friction weld tech to join the 2 halves together along with the mounting pads (for the flex plate) these creating hard spots on the circumference and where the mounting pads are. As time passes these areas start to Crack and break, the pieces are caught in the converter pump and sent through the transmission and they destroy the tranny. I took the proceeds from selling my S 10 and motorcycle to pay for a top of the line rebuild using correctly (non GM) made parts. Also to reprogram the tranny you have to take it some one who has purchased the software or a GM dealer.

Edited November 26, 2024 by dna9656