Hi, I have a 1990 2500 Suburban with the 454 and THM400 transmission in it. It's recently (in the past couple of days) developed a strange problem. When I put it in drive the tranny will slip like it's not quite in gear but put it in second and it's okay. It will shift from first to second normally then if I put it in drive it slips. However, if I'm getting on the freeway and wind it up to about 50 then put it in drive it shifts normally and from that point on as long as I keep it in drive, it will shift as it should. (get off the freeway, make stops, etc and it shifts perfectly fine with no slipping) However when I put it in neutral or park then back to drive it's slipping once again.

Today I changed the tranny filter and put in 6 qts of fluid to bring it back up to the full mark (tranny warm idling in park) but it is still doing the same thing.

It does not look as if the shifting linkage has moved at all, but of course I can't be certain. I bought it used and it's always had the quirk of it won't start in neutral, but put it in drive and it'll turn over and take off. And of course the PRNDL is off a bit but hey, it's an older Chevy...

Any ideas?

-mike

 

adjust your linkage correctly,check that detent is connected inside and out, and that detent is operating correctly,check vacume modulator works if its still doing it check the pump press.. it might have messed up your valves in the valve body from improper adjustment

 

At this point I'm swapping it out for one I found with ~500 miles on a Goodwrench rebuild. I do have a new post about the speedometer sender though. Please take a look and see if you have any ideas.