I'm hoping somebody will have a bit of knowledge to help with my problem, so here goes...

Until yesterday my '72 Cutlass Supreme had a 10 bolt O axle with 2.73's and an open carrier and 28 spline axle shafts. We disassembled the axle to put in an 8.5" GM posi unit with Richmond 3.73's. After getting the desired tooth pattern and backlash we went to put in the axles and discovered that the posi unit needs 30 spline axles while mine are 28 spline.

I was told by a friend that the Olds 10 bolt and 12 bolt axles are the same length, they just have different spline counts. So if this is true can I buy a pair of aftermarket 12 bolt 30 spline axles and put them in my 10 bolt?

 

NO.You are not getting correct information.You either need to switch the posi carrier for a 28-spline carrier,or you will need to order a new set of 30-spline axles.
If it is a "GM posi unit",and it is 30-spline,then it is either an Auburn,or a Gov-lock.
Can you post a picture of the unit?

 

I can't post a picture of the posi unit right now because the car is at a friends house for the time being. I'm ok with buying new axles, but does anybody make 30 spline axles for my 10 bolt?

And the other thing I've noticed with aftermarket axles is that all of them I've seen for GM car 10 bolts are c-clip axles, so I would have to buy the c-clip axles and a c-clip eliminator kit for them to work on my axle, correct?

 

I've had 30-spline axles made by Moser numerous times.They are still the same bolt-in axle,with the same bearing/retainer configuration.They just have a thicker shaft & 30 splines.

 

Ok so I have to have custom axles made?

 

Yes,they are about $450.00 +/- by the time you get bearings,retainers,wheel studs,and the shipping.
If you gears are set,you can leave the pinion alone,swap the carriers,and recheck your backlash.

 

I did see on the moser website that they build custom axles for $350/pair. So when they make the axles I can still use stock bearings with moser axles right?

And the gears are already set, but the backlash isn't perfect. Richmond recommends 10 to 12 thousandths and it's set at 16 right now. Will that cause any problems?

 

.016" is way too much. Yu need to nail it down between .008"-.010".Get as close to .008" as you can.
As for the axles,Moser will make them for the 712146 seal and SET9 bearing,which is what your stock axles have.You can also ship one of your shafts to them,and just have them make a pair for 30-spline.

 

I called moser this morning and I'm going to do exactly what you said, ship them one of my axles and have them make a pair with 30 splines. As for the backlash, I guess when I get the new axles we'll take everything back out and get it closer.