Questions and Answers

GMC Sierra K-1500 Shifting Crazy Q. Hello Vincent, I have a 1990 GMC Sierra K-1500 (4x4) 5.7 liter with overdrive and 300,000 kilometers (186,411 miles). Truck started shifting harsh right after a new flywheel was installed (after some 15 minutes of driving). After another five minutes of driving problem suddenly went away, shifted fine for a month, then came back more severe this time.

Now it does not shift until rpm is very high and does not shift to overdrive at all. Sometimes not even to third gear. When I put it into reverse, it won't engage when hot. I have to shut engine off, wait a couple of minutes. After that it usually works. Sometimes it has a slight delay before engaging, same thing when you put it in drive.

There is a noise coming from transmission while in park or neutral, not in drive or reverse. Fluid level was high, I pumped some out but problem persists. Could it be something as simple as a bad filter or the TV-cable not correctly adjusted? But with the noise WHEN HOT I mentioned, maybe not. Any ideas?

Thank you,
Tommi

A. Sounds like something may be coming apart inside. The noise could be a buzzing noise from the pressure regulator. Maybe getting air in the fluid? I would pull the pan to see if anything is in it. Could be a cable adjustment if you think you disturbed it while doing the flywheel.