OK, not the greatest title, but whatever.
My '67 Barracuda has a GM 8.2 rear end on it, for who knows what reason. I found a 8 1/4" 3.21 4.5" bolt pattern open rear end that's already had the perches moved for an A-body. Problem is it's supposedly 63" flange to flange, but the guy didn't get around to narrowing it because he found a 8 3/4". The price is too good to pass up. I've never narrowed a rear end, but I do know the axle tubes and axles will need to be shortened. Are the axle tubes something a typical driveshaft shop would do? As far as the axles themselves, shorten them (if it's doable)? Or am I better off looking for a set of new or used axles?
This is going behind an A833 trans with a 360 Magnum engine. No outrageous HP
Always more than one way to skin a cat. There are Youtube videos on how to narrow a Ford 8.8.
Strip the axle housing. How much do you need to narrow it? In the case of the Ford, 2 7/8" can be cut from the long tube and get a new short axle to use. The diff housing will be centered while the driveshaft will be at a slight angle. This is not a problem. Then the perches need to fit the width for the springs.
The procedure involves cutting the chosen amount out of the tube. Use a shirt cardboard or equivalent to mark a straight cut line about the center of the tube, but closer to the outside. Measure over toward the diff housing the amount desired to remove and mark the inner cut line. Using a cutoff disc in an angle grinder and about 1/16" on the side to be removed, cut the outer end off. Then cut the "to be removed piece" off the tube 1/16" from your cut line.
Two pieces of 2 1/2" channel about 16" long and a couple of C clamps will hold the sections square. The length shold be measured between the diff casting and the brake flange before and after cutting. The 1/16" left on allows trimming for a square fit for welding. If a line is marked before cutting horizontally on the tube, this can be lined up so the brake brackets are level side to side.
Some axles can be narrowed and some can not. If just the long side can narrow it enough, a new axle for the short side can be purchased. A word of caution, word has it the axles can take a "set" and may break if a short axle from a recycle yard is used.
If your axle uses c clip retention, differential companies like Mark Williams and Currie to name two, can supply the Ford large Torino housing ends to weld on. This gives the pressed on bearings required for most racing. With that though you need to purchase new axles with a step to press the bearings to, and the bearings with retainer plates.
The other method is again measure the length from the center housing to the brake flange. There is a couple of kits available if you intend to do a bunch, that keeps the tube straight. This method after stripping the housing requires using a hole saw to cut the rosett welds holding the tube into the center housing. Use a die grinder to clean up around the holes. The tube can then be pushed out. Cut the desired amount off and press the tube back in. Double check the length measurement. Tack weld at first 180° and then 90° to those at the outside of the center section and the tube. Use a dial indicator as the housing is rotated on axle stands to verify it is straight. At this point if there is runout, the tacks can be ground and the housing put in a press to get it true. Tack again and retest with the dial indicator. Reweld in the holes and around the tubes. Only do 90°around and then turn it 180° and weld another 90°. Then finish the rest.
If both sides are to be narrowed, I would complete one side before moving to the other side.
If you need to order axles, consider spline count. Going to this much work, I expect a bit of LSD is to be tossed in. The axle supplier can also provide the carrier with spline count and axles machined to match.
