Straightening a rear end housing
Here's how to make a fixture and rack for straightening a rear end housing.
 Building a straightening table
The straightening fixture pictured below is an old garage sale compressed gas cylinder cart, with its top cut off. A 6" X 6" I-beam was then welded to the cart. You don't need a cart, any table with sturdy legs will do. This cart just happened to be handy and had nice wheels so we could wheel it around the shop.
To prevent any mishaps involving slippage and gravity, common jack stands are cut up to wrap the leg of the I-beam. The bottoms were notched and a slice made at each corner to get the stands fitted to the I-beam.
A straight bar is necessary. This hardened and chrome-plated bar is about five feet long, and 1.5" in diameter. It's available from McMaster-Carr for about $115.00. Alternatively, an old length of scrap steel shafting can be used. V-blocks and a dial indicator can be used to verify that a used bar is straight. Smooth, round and straight is best. You could use 1" round bar but the accuracy will suffer. One of the manufacturers that sells these alignment fixtures uses 1-11/16" bar. Bigger than 1-3/4" and the bar will begin to become too unwieldy to handle easily.
 Making the inserts
Then, make some inserts. These are about 2" long, as to provide some load bearing area to lessen wear caused by repeated use. For this application (10-bolt Chevrolet), the ID is 1.504", and the OD is 2.894". These same size inserts will work in an 8" and 9" ford center sections as well.
Another insert was made with the same 1.504" ID and dimensioned to slip-fit into the housing end. This same set of inserts and matching bar can also be used as an alignment aid when narrowing rear end housings.
The inserts are then clamped in the bearing saddles and the bar slides through them. The fit should be snug; the bar should slide through easily, but with no noticeable play.
Here is the inserts are installed in a Ford 9" center section. The bar is slid through before the bearing caps are tightened, to make sure they are aligned in the bearing saddles.
Another way to determine if the housing is straight is to machine the inserts for the diff center with a small center hole. Clamp these in and install center in housing. Then using a sheet of paper with a small hole held at the bearing end, sight through and line up with two holes that are in the center. Then run your finger around the tube end marking the paper. Find the center of you mark and this will show you how far your diff is out by comparing the hole in the paper to the center.
The housing end insert slides over the bar and indicates how much the end of the housing is bent out of alignment.
Hold a ruler on the tube to see where it's bent. In this case, it's bent at the areas that were welded by the previous "builder".
 Heating and bending
Next, rig a chain at the point of bend and put a 12-ton bottle jack under the end of the axle. To prevent bending the center casing, attach the rear cover or a fabricated piece of thicker steel flat stock drilled with the bolt pattern of the cover to provide better support.
You can try to bend the axle tube at this point, without heat. If you want to bend the tube in this way, push the tube approximately 5 times the amount you want it bent. In other words, if your alignment is off by 0.030", you need to push the end of the tube about 0.150" or more to overcome spring-back. If your axle housing end is off by more than 0.100" from the alignment jig, you will probably need to use heat.
If you find that you need to heat the axle tube, jack up the housing into perfect alignment with the housing end insert and heat a band all the way around the tube until it's red-hot. Let the tube cool while it's still supported by the jack.
In this case, when the tube cooled, the housing end was only a few thousandths of an inch off, and was easily bent into alignment cold, using only the bottle jack. This housing was initially out by almost 1/4" on one side, and 3/16" on the other. Now, the housing end slips on with minimal effort.
 Related information
- Hotrodders bulletin board thread, Straightening a Rear End Housing