I'm brand new here, I figured if no where else I could possibly get a good answer here. I have a 1990 with a 4.0 OHV and automatic trans. This thing has been giving me issues since day one, the last guy wasn't the sweetest with it. When I got it I immediately had to replace the oil pan gasket and for a good 6 or 7 months, never had a problem with it. One day I was driving it home, and it started to do this thing where it would shift through all the gears just fine until it got to overdrive, and as soon as it would shift into it, the truck would start to rapidly kick and shake. It primarily did it the harshest the lower the mph was. Scared the hell out of me the first time. Ever since, it's been doing this. I've searched all over creation for the answer to this issue. So far, in this order, I've replaced the fuel filter, pressure regulator, fuel pump, spark plugs, wires, coil pack, and MAF sensor. No luck. I've heard a clogged catalytic convertor can bog the truck under load but that's a last ditch effort I really don't want to deal with unless necessary. I'm flat out of ideas as to what the cause of it is, but it just strikes me as strange that it only ever does it in overdrive! If it helps any, the truck also makes a strange squeaking sound from what I think is the rear end and sounds like there's a rubber ducky strapped to the tire, only when the truck is moving, and the exhaust smells off (not sure if either correlate to the problem at all). Is there something I'm missing? Any help whatsoever would be greatly appreciated.

 

Welcome to the forum

When you drive around in D and don't use OD do you still have the problem?
I think you answered that but what to be sure

If it only does it in OD and not D then you have a transmission problem

You can test for blocked exhaust with a Vacuum gauge, get one, they are cheap and about the best diagnostic tool ever made for gasoline engines

 

So yes, when I drive around with overdrive disengaged (because it's got it's own gear) it doesn't happen whatsoever and it's smooth sailing. Only happens when that OD gear pops in.

I'll have to give that vacuum gauge test a try, thanks.

If it's a trans problem, then what part of the trans do you think is causing it to happen only in OD?

 

First guess would be out of round OD Drum, so full rebuild to change