1990 gmc vandura 2500, odometer was frozen when we bought it. It looks like someone has pushed the trip odo reset, and it didn't quite get to zero.
It reads all 1s.speedo works fine, but the (automatic) tyranny slams from 1st to second if under a load. Does not slam if shift happens on a decline, or if I back off acceleration, to let it shift easy. Other gears shift softly. Troubleshooting tips, anyone?
Shifting issue automatic tranny
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Prairiewoman068
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MountainManJoe
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Re: Shifting issue automatic tranny
Start with the basics. Check the level and condition of the transmission fluid.
When is the last time the transmission was serviced (fluid + filter change)?
Welcome to the forum.
When is the last time the transmission was serviced (fluid + filter change)?
Welcome to the forum.
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Bret Schmerker
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Re: Shifting issue automatic tranny
The THM400 and its replacement the 4L80-E can clog the valve body if neglected. I'd had converter-clutch slip in my now-down-until-further-notice GMC M11006, traced it to normal wear and tear in a stock 4L60-E that should've had an overhaul at 200,000 miles.
1997 GMC M11006 (Safari SLE, 2WD, V6-4300/4L60-E/7.625" 3.73:1 open)
Acquired Jul 2018 / In service Sep 2018 - Nov 2022 / down due leaky valve(s) #5 cyl.
Acquired Jul 2018 / In service Sep 2018 - Nov 2022 / down due leaky valve(s) #5 cyl.