We then tapped a spacer into...
We then tapped a spacer into the bottom of each perch and welded it from the top.
Next, we placed a large wooden block under the perch on the right-side axletube and another block under the left-side axletube where the perch used to be. Because of the one-inch difference in leaf-spring spacing between the A-Body and B-Body, we had to locate each of our new perches inward 1/2 inch on each side from the factory location. We placed a new perch between the left side axletube and the wooden block and positioned it 43 1/2 inches from the right-side perch. (Measuring from the inside edge of one perch to the outside edge of the other yields the same reading as measuring from center to center, and it's a lot easier.) Using wooden blocks or cinder blocks, and doing one perch at a time assures that the new perches will be angled at the same orientation around the axletube as the original ones. This way, the rear U-joint angle will remain the same when finished. We scribed the perch's location on the axletube and then welded it to the tube. Next, the right-side perch was removed, and the new one positioned 43 inches from our left-side perch, again using the wooden blocks. Once we marked its location, it too was welded on.
We ground the spacers flush,...
We ground the spacers flush, then drilled the centers with a 1/2-inch bit so they would properly index the axle to the locating pins/center bolts of the leaf springs.
With our new perches properly positioned and welded in place, it was time to reassemble our axle. Upon completion of our rear axle swap, we had a pair of 14x5 1/2-inch Rallye wheels widened 2 1/2 inches to the inside. Then we mounted and balanced a pair of P245/60R14 tires on our new 14x8-inch wheels. They fit nicely within the narrow confines of the Dart wheelwells.
Although we chose to widen the Rallye wheels, the availability of aftermarket wheels is excellent these days. if we had chosen to go that route, we simply would have ordered wheels with the desired offset. If we were working with a Duster, Demon, Dart Sport, or a '67 through '69 Barracuda, the open rear wheelwells would have afforded more space, and the clearance wouldn't have been as much of an issue as on our Dart. Once the axle is installed, the rear U-joint angle should be checked with a driveshaft angle gauge.
We placed the housing on a...
We placed the housing on a pair of large wooden blocks. The housing did not rock, indicating that the new perch is on the same plane as the one on the right side. We measured from the outside of the original right-side perch to the inside of the new left-side perch to correctly locate it 1/2-inch inboard of the original location. We then welded it in place.
We replaced the right-side...
We replaced the right-side perch in the same manner as the left side, then verified its location. Again, the housing did not rock on the wooden blocks, and our measurement was now exactly 43 inches.
If your original carrier-to-housing...
If your original carrier-to-housing gasket remains intact, a thin bead of silicone sealer will help ensure that there are no leaks. If your gasket tore, it must be replaced. Torque the nuts to 45 lb-ft.
Using an appropriately-sized...
Using an appropriately-sized seal driver, the new seals should be driven in until they bottom, typically to a depth of around 2 5/8 inches from the edge of the housing.
With the axle bearings cleaned...
With the axle bearings cleaned and packed with fresh grease, the backing plates are placed on the studs, and the axleshafts are slipped into position using extreme care not to damage the new seals. The axle-retaining nuts get torqued to 35 lb-ft. Rotate the axles several times to seat the bearings, then check the axle end play with a dial indicator. It should be between .013 inch and .023 inch. We usually set it toward the tight end of the spec. The center of the right-side axle retainer turns to adjust the endplay. When it is correct, remove one nut and install the adjuster lock under it.
If you are swapping out a...
If you are swapping out a 7 1/4 axle in favor of an 8 3/4 axle, remember the axletubes on your old axle are 2 1/2 inches in diameter, while the tubes on the 8 3/4 unit measure three inches. This means your original bottom plates and U-bolts cannot be reused. These pieces can be recycled from the B-Body that donated the axle. be sure to take the special bolt that secures the brake hose to the 8 3/4 axle because it incorporates the rear-end breather. Furthermore, you'll need to have your driveshaft shortened 2 1/4 inches.
To make the wider B-Body rear...
To make the wider B-Body rear work in our Dart, we needed to relocate the centerline of the rear wheels. In addition, we needed wider wheels to accommodate fatter tires. After a lot of measuring, we had the inner portions of a pair of 14x5 1/2-inch Rallye wheels cut off, and 2 1/2 inches added into the wheels. Our new 14x8-inch wheels allow a pair of meaty 245/60R14 tires to fit snugly between the wheel lips and the leaf springs, while allowing full tread contact with the pavement.