Hello guys I have a doubt in my head. Before I put my Cougar on the road, I freshed up my differential. I got a kit from Randy's ring and pinion and re did it. The carrier bearings they sent me were for a 28 spline because thats how many splines the axles have. But those bearings were to small. I called back and they said that those were for a 28 so if they didnt fit I have a 31. I counted those things like 5 times. They sent the bigger ones and they fit. So im confused. Also the o ther day I was trying to remove a one of the hind wheels. It was so tight that the wheel moved and made a grinding noise. Does that mean the axle is smaller than the spline in the spyder. Give me some info. I wanna make it a posi and I want to get the right one.  

The difference in bearings and splines is simply a matter of carry over production of a small batch number.i.e maybe your diff has the first production batch of the bigger bearing,then the company decided(probably for good reason)to go with the 31 spline axles,or vise versa...........The hind wheel? I'll assume your reffering to either the crown or pinion gear.When pulling the axles,sometimes you have to use a slide hammer as they can be very tight,requiring a few stern slides of the hammer to pry them loose......for fitting the axles,always apply gear oil to the splines and any mating surfaces...The grinding noise sounds strange? I hope your not talking about the backing plate bolted to both sides of the diff?........As they often "shriek"when removed from the studs,if so thats nothing to worry about.  

If the normal 2.891 bearing was too small, then you have a case with 3.062 bearings.  Has nothing to do with spline count, although the larger bearing cases typically show up in 31 spline units.  A 31 spline axle will also fit in a 2.891 bearing case.  If the parts you have came out of the car, then they should all work together.  If you are piecing this thing together, then you need to pull the center and count the splines in the spider gears.  If the axles mate and seat in the carrier, and then it won't move or makes noise - you have some internal problem.  I assume since you "freshed" the center that you have all the right tools - press, spanner wrenches, dial indicator - and set it up with the correct bearing preload and backlash.

> I wanna make it a posi and I want to get the right one.  
"Posi" is a GM term.  If you want to run a locking or "limited slip" type diff (Ford calls Trac Loc), then you buy one that matches your axle spline count.

Some Ford 9" Tech