SadbutTrue said:
And can i use any 9 inch case with any 9 inch third member with any 9 inch axles? What can interchange between all 9 inch rearends and what can't?
Some axles are 28 spline and some are 31 spline, so no, you can't.
Also, there are big bearing housing ends and small bearing housing ends.
Narrowing a housing runs about $150 and requires a fixture to make sure the ends are perpendicular to the axle centerline and that each end lines up to the other end AND passes thru the centerline of the carrier. You'd be suprised on some housings to cut the housing ends off the housing, and install the fixture and slip the ends back on without narroing them any, and see how much the housing was out of alignment. The fixture consists of a thick walled tube that is trued to be perfectly straight, a bare center section with aluminum bushings where the axles would normally enter the carrier for the tube to pass thru, and set of bushings that the center will slip over the tube, but the outside is made for the axle bearing recess in the housing end. Usually there are a couple of these, one for big bearing and one for small bearings.
You're existing 8" axles will fit in the right 9" housing and you can even use the drum brakes off your 8", but I'm not sure which housing it is and it's probably hard to find one that is the correct length. If you can find a passenger car with a 9" with the right housing ends, you could have it narrowed and use your axles and brakes. Now if you want it narrower, you need to check your spline engagement on your existing axles, or whatever axles and housing you intend to use. When you pull an axle out, you can see that the splines are longer than where they fit into the carrier. I've seen budget narrowed rears that needed an 1" narrower on each side, the housing was narrowed and an 1" of axle was cut off each end and the end beveled with a grinder to mimick the stock look (makes for easier engagement) and the ends of the splines where cut were cleaned up with a small triangular file. If you have a higher horsepower application (above 400 horse) you'll likely want 31 spline axles and I think those were only in trucks (way too wide) and large land barge type cars (Lincolns and old station wagons.
Another thing to consider, and I didn't read your wheel/tire post, but if you're considering late model wheels, by using a bit wider rear end, you'd eliminate the need for the spacers and longer studs on the rear.
You can also be lucky like me and have someone give you a chromed (and rust) '57 station wagon 9" with 3.50 gears and a Trac Loc.
