So my rear differential is toast and for some reason, it is very difficult to find a used one with the correct gear ratio. I keep finding ones with 3:55 gear ratio but no 3:90. Is it possible to rebuild the one I have and how difficult would this project be?
thanks in advance!
Sam

 

How bad is your current rear?

 

Setting up gears in a rear end is one of those things that take a certain talent. I don't have it. You have to deal with preloads, shims and such. If there's a commercial component place that rebuilds major assemblies, or a driveline place nearby, they can do it for you. The 3.91 was an option that most people didn't go for.

 

Pretty bad the gears are chewed up to hell. I was on the freeway going 70 miles when something broke loose.

 

Any good resources to find the whole assembly used? I can't seem to find one and I've been to many junkyards/Pick&pull to find one but no luck.

 

Try car-part.com and search for a rear axle for your year your type.

They show several 3.9's for a 1988 in the USA; some may be near to you!

RwP

 

You can either keep looking for another rear or put a 3.55 in and change the speed sensor. With it grenading going down the road, you have junk all through the unit. 3.55 is a good utility gear, does fine for medium towing and will give you better fuel mileage. I had one I bought new and it had the 3.55. Great truck. In 180,000 miles I had the steering rack fail at 110,000 and just maintenance other than that. You may find it's more of a hot rod with the 3.55.

 

I rebuilt the one in my 96 around 40k miles ago and added a new traklok limited slip at the same time. It too is a 3.91. the other 5 Dakotas I have had were all 3.55 trucks. My gears were fine, on mine it was the pinion bearings that went bad, I replaced all 6 bearings with in the rear end and all 3 seals at the time.
Tracklok came from my stash, bearing kit was $140, which never comes with outer axle bearings or seals but those can be had cheaply and that's even for the good brands.

 

I was told by a mechanic who specializes in differentials that I'd have to change the whole front end assembly otherwise it would ruin both. He would have told me if it was just changing the speed sensor.

 

This is why you need to say what you have. I didn't know it was 4X4. Your differentials need to be gear matched. For a 3.55 rear end, you'll need 3.54 in the front to keep the transfer case from over running.