i have a 74 roadrunner with a 8.25 rear. i bought a nos posi unit for it. i also bought 3.55 gears out of a 96 jeep. the problem is that when i install the carrier in the housing with the ring gear on it the pinion gear will not mesh correctly. am i supposed to use a pinion bearing from a 96 jeep? i have new bearings on the carrier for a 74 roadrunner.

This really isn't a job for a first timer. The ring and pinion gears are a matched set, and setting them up requires a few specialized tools. If you tried to keep the original pinion gear in the housing, its a bad idea. If its a different ratio, theres no way it will work. The tooth count on each ratio is different and they will not mesh. Also, POSI is a Chevrolet term. Mopars used the name Sure Grip.

Isn't the jeep rear a Dana? never work

I think after 1998 the 8.25 rear was designed so earlier parts may not interchange. Not sure 100%, but I do remeber somebody on here posting a similar thing that happened.

Spline count in the sure-grip is different on the newer stuff. I don't know that there is much difference in the gears alone.

I will say however, that setting up a ring and pinion properly is a job. I'd look into the local 4x4 shop. They do it all the time. I know a guy who does several vehicles a week front and rear.

It is possible to do yourself, but it is pretty crucial that you get things right.

ROB

Was the sure grip unit for a 2.45 gear set? If so this is the problem. There are lots of these out there for sale right now. If you install the ring gear on your original open carrier will it set up?

The 96 ring and pinion should not be an issue. I installed a 3.55 from a Jeep in my Duster with no problem at all. The spline count did change on the carrier on later ones but the gears were not affected.

i am not doing this myself. the car is at a shop. the car had 3.21 orginally and the carrier i bought is for these or 3.55's. i remember reading somewhere that the bearings changed during the production run.

Now that you mention it, I think you're right on that account to.