Stupid question, but I only have a big bearing axle infront of me to compare.... Wanting to know it the axle shaft diameter is the same on all 9" (31 spline?) Meaning, can I just swap from big to small bearing (and backing plate) or the other way around and the axle will fit its associated housing?
There are two "big bearing" types. One is the 'sealed' bearing that is manufactured with grease inside and uses an axle oil seal a bit deeper in the housing to prevent differential lube from reaching the bearing and leaking to the brakes.........the other is commonly called "Torino" style and is a tapered roller bearing on the axle shaft with a seperate bearing cup pressed into the axle housing and the seal for that one is OUTBOARD of the bearing as the differential lube is used to lubricate the bearing. Not only are the bearing/axle shaft sizes different, but so is the housing and the brake backing plate offset from the axle flange. The early style is offset 2 3/8" and the later 2 1/2" (it is possible I have that in reverse order, but those are the dimensions in either case) It is possible to replace the axle housing ends to use one or the other on a given housing, but that requires cutting/welding/alignment and careful measuring. Ray
All factory 31 spline axles are the same, and all of them are big bearing. Small bearings have a smaller ID than big bearings. Moser has a replacement bearing that will fit a big bearing axle, and a small bearing housing.
There are small bearing 31 spline axles and big bearing 31 spline axles, and they are NOT the same. The brake offset is different as well as the diameter. Stay away from the Moser adapter bearing that allows a big bearing axle in a small bearing housing, as the ball bearings are not big enough to handle the load and THEY WILL FAIL in as little as 500 miles.
You are correct. I forgot about the 67 to 73 Mustang/Torino rears which had a small bearing and 31 splines. The only thing I have used the Moser bearing on was drag cars, and had no problems.
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