gordr
New member
I have a '97 GMC 3500 4X4 Suburban, 5.7 liter engine, and 4L80E transmission. It has been very reliable since I have owned it; bought it in '07.
Recently, the transmission has been throwing hard shifts, especially the 3-4 upshift. Did this for about 2 days, then went into limp-home mode, and only went forward in second gear. It was idle for two days, and on Wednesday last, I started it up, and for the first mile or so, it shifted perfectly, all four gears, then went directly to limp-home. I searched on the internet, and one suspect was the vehicle speed sensor, located on the output shaft end of the transfer case. Changed that, and woo-hoo! I had four gears again, and smooth shifting. That lasted a whole 5 miles, and crap!, back to limp-home.
Took the tranny pan off; extremely clean inside, zilch for sludge or metal trash. Checked resistance on all the solenoids, and on the tranny fluid temp sensor; all within spec. Cleaned the filter with the solvent that dare not speak its name, and buttoned it all back up, and refilled it. Drove it ten minutes ago. Limp-home mode right from the get-go.
Where do I go from here?
Recently, the transmission has been throwing hard shifts, especially the 3-4 upshift. Did this for about 2 days, then went into limp-home mode, and only went forward in second gear. It was idle for two days, and on Wednesday last, I started it up, and for the first mile or so, it shifted perfectly, all four gears, then went directly to limp-home. I searched on the internet, and one suspect was the vehicle speed sensor, located on the output shaft end of the transfer case. Changed that, and woo-hoo! I had four gears again, and smooth shifting. That lasted a whole 5 miles, and crap!, back to limp-home.
Took the tranny pan off; extremely clean inside, zilch for sludge or metal trash. Checked resistance on all the solenoids, and on the tranny fluid temp sensor; all within spec. Cleaned the filter with the solvent that dare not speak its name, and buttoned it all back up, and refilled it. Drove it ten minutes ago. Limp-home mode right from the get-go.
Where do I go from here?