85 GMC Sierra 1500 won’t shift.

Asked by Cameronmurphy90 Dec 06, 2020 at 04:14 PM about the 1988 GMC Sierra 1500

Question type: Maintenance & Repair

have a 85 GMC Sierra that is having trouble
shifting into any gear. When I’m in park and
it’s running after I’ve let it warm up it’s not
going into gear. There is a loud “whine” that
starts as soon as I shift it into any gear. If I go
into reverse I don’t hear the RPM’s change
and can feel the truck want to start moving
backwards but then stops. When I apply gas
the whine increases and the truck starts to
move it just seems like I’m needing too much
gas to get it to move. i’ve crawled  underneath
and can see that the shift linkage and arm is
connected into the tranny and I can move it
freely with my hand. All the fluid levels are
good and no obvious leaks. Please help

1 Answer
155,245

james answered 3 years ago

Check for a disconnected vacuum hose going to the vacuum modulator on the automatic transmission. I think GM was still using that set up in 1985. It should be on the passenger's side. The vacuum modulator is a round gizmo that is on the side of the transmission with a nipple for the vacuum hose on it. The leaking vacuum would account for the whine as well. Hope that helps! Jim

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