Thread: Narrowing a 9" ford rear end

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I don't know what the tolerances are, but they must be somewhat generous cuz a lot of stock rear axles get mildly bent along the way.
Due to jacking in the center etc. and most times bearing life isn't affected to any great degree and there's usually no difficulty in pulling or replacing an axle.

The professionally narrowed rear axle in my 32 is further off as compared to the narrowed axle I did at home for my 31.
The narrowing was done on a frame table, but a flat piece of channel or I-beam would work ok for a base.

Only additional thing needed is a couple of 4" x 1/4" angle brackets drilled to match the axle tubing ends where the axles proper bolt up.
These allow clearance for the punkin and when clamped to the frame table - or other flat surface - assure a 90 degree fit vertically.
the 90 degree horizontal fit can be easily checked with a couple of flat bars and a tape measure.

After things are tacked, measure with a digital level and see how things came out.
Turn the axle housing 90 degrees so you can check the horizontal alignment.
If you measured carefully between the flat bars it should be right on the money.

Checking done with a digital level that's accurate to a few seconds of arc.

You're probably cutting a 61 1/2" wide (measured outer drum to outer drum) axle down to 56" - which is a common width for most hot rod installs.

Cut the axle tubing ends off just inside the factory weld.
Machine the weld off the axle ends and generally clean things up.

Cut the axle tubes to size allowing for the length of the axle ends so as to end up with the width you want.

A little clean up of the axle tube's ID and chamfering the inner edge a touch - a drum sander on a 3/8" drill motor works fine - allows the axle ends to be tapped in with a soft hammer.

Put a fairly good chamfer on the outside edge of the axle tube for good weld penetration.

Align, make four strong tack welds 90 degrees apart.
Complete the weld by welding the area between tacks.
Do the first two welds at 180 degrees to each other, let cool to ambient temp and do the other two welds.

Butt welding the axle tubes probably works ok, but it's better to do it like the factory did.

Factories do things for a reason and if butt welding really was good enough you can bet they'd do it just for the savings in $$.