Has anyone shortened a rear axle shaft?

alchemy

alchemy

Well-known member
I’ve got a few good 42-48 rear axles, and need a few good 40 axles (supposedly 0.85” shorter). I’ve also got a buddy with a CNC lathe in his hobby shop. Has anyone here ever shortened the tapered end of an old Ford axle shaft? Any tips or advice?

Wondering about surface hardening, the taper measurements and angle, or any other things learned in your experience.
 
alchemy said:
I’ve got a few good 42-48 rear axles, and need a few good 40 axles (supposedly 0.85” shorter). I’ve also got a buddy with a CNC lathe in his hobby shop. Has anyone here ever shortened the tapered end of an old Ford axle shaft? Any tips or advice?

Wondering about surface hardening, the taper measurements and angle, or any other things learned in your experience.
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I can tell you this... I was a tool & die maker and what you propose to do is most likely well beyond the capacity of a cnc lathe in a hobby shop.
The angle has to be PRECISE. Cutting the angle back over the keyway on a lathe? Good luck.
Yikes, the more I think of what you propose as I respond, the more issues I imagine.
If '40 axles were simply not available at any cost and I was FORCED to make one out of a '48 axle, I'd think I'd cut the shaft and weld it.
Even that is not something most "hobby shops" would be capable of doing properly.
 
I have no idea but the drag racers have been cutting axles for years, cut some place in the middle and weld, lotta work but can be done.
 
kurt v said:
I have no idea but the drag racers have been cutting axles for years, cut some place in the middle and weld, lotta work but can be done.
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Per my previous post, that's the way I'd do it IF I had no source for a correct axle.
 
Here's related question. Could a good machine shop make a good '40 axle out of a "bunged up" later one?
 
Are good 40 axles that difficult to find? I'd check Early Ford Parts in San Dimas. They had a lot of early Ford axles when I was there in June. Also Southside Obsolete
 
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I was asking because I’m a cheapskate, my buddy doesn’t charge me much, and the 48 axles would probably go to waste otherwise. Mr. Kube, say I could get the angle figured out, is the surface hardened or is it really deep? And I do understand what you are saying about the interrupted cut over the keyway.

My buddy cut the splined nose down on a pinion gear for use in a quickchange on his Hurco lathe. The cut wasn’t really good because by the time he got through the hardness at the top of the splines, he was still trying to cut through the hardness in the root. Soft vs hard doesn’t make for a smooth cut.
 
Remember the taper is the friction fit that drives your car, not the key itself. You have to get the taper right (proper angle, surface finish, concentricity, etc.).

If you had a full machine shop with professional equipment and wanted to shorten a later axle without cutting and welding I would try: extend the cut of the threads (match the existing threads with a single point cutter), rough turn the taper leaving at least 0.020 to clean up, precision grind the taper on a good grinder with a table you can pivot and very good gauging, mill the keyway slot deeper (good luck matching the existing slot), and cut the "bunged up" threaded end down to length.


I'm with Kube, no way would I try that.
 
40 years ago, I was educated as a mechanical engineer. What you propose is high risk. The heat treatment of a stock axle is likely acceptable but not uniform from surface to center. If you shorten the axle, you're digging into the heat treatment with unknown consequences. You're playing with fire.



If there's any way at all you can acquire a new unmodified axle, do that instead. If you use a modified axle, don't drive too fast. A few passes on the drag strip may be OK but don't drive the vehicle tens of thousands of miles.


Several years ago I broke an axle going 70 mph on a state highway. Very fortunately the disc brake caliper on my disc brake conversion held the wheel onto the car rather than allowing the whole rear body to belly drag (it was a totally awesome blue smoke screen as the tire disintegrated going from 70 to 0.) Without that disc brake conversion holding the wheel in place, the car would have been totaled.



Doing the forensics, it was very clear someone had removed the rear axle bearing with a cutting torch and left a very small nick in the axle surface. Over 20,000 miles of rotations of reversed tension and compression cycles, that tiny nick had worked its way though the entire axle until it broke.


Just saying that hardened steel, like axles, is extremely difficult and unpredictable to machine. You really need to do the heat treatment AFTER machining.


When I'm betting my life, I tend to be conservative.
 
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Hasn’t anyone ever assembled an axle set leaving the keys out altogether? As they are not needed if the taper is in good shape and torqued correctly, if you’re going to cut a new taper, just don’t cut the keyways at all?
 
ford38v8 said:
Hasn’t anyone ever assembled an axle set leaving the keys out altogether? As they are not needed if the taper is in good shape and torqued correctly, if you’re going to cut a new taper, just don’t cut the keyways at all?
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This is what I have contended every time the subject comes up, that the keys are not what transmits the torque to the hubs, just like a Morse-Taper. I'd sure like to hear from someone that has actually done this with success.

Coop

.
 
I agree, its a precision task, but I believe Lawrie from down under has done it, at home, with a manual lathe. Lawrie checks in frequently, so, he will call me a liar, or tell you how to do it
 
To all of those that have never done the specific job in question, I have done it many times and many variations of same. Probably only for racing 95% though.
In racing things are stressed at least 10 times more than expected for street use and expected to be replaced or fail after short term use. However, a race part installed in a street application will the majority of the time far outlast a common street part.

Shortening axes and narrowing rear ends was a very common job "in the olden dayz".
We shortened them and re-tapered them. We cut and welded in the middle, usually on late models, and we cut splined ends off and mated them to early banjo and other center sections.
We had state of the art welders then, now the stuff is even better. We had plain lathes with taper attachments. 75% of the jobs never got near a heat treat furnace after we finished them and we had almost NO premature failures.
The main things that kill these type of mods are poor alignment, poor welding skill, wrong rod and poor procedure.

I made rear ends for one of the most prominent race teams in the US (still racing) at one time and some of those are still in use so don't be afraid of trying something. It will most likely work if done right.
One important note, tapers need to fit perfect. They should be lapped to 100% contact surface. Axle nuts for taper hubs need to be at least a grade 8, HARD HIGH NUT and torqued to SAE chart specs for that size thread, NOT some back yard hearsay number. In many cases the final successfuI torque is considerably above the chart number.
If you can not get the proper torque reading or the thread feels like it starts to strip it is doomed for early failure. Axle nuts DO NOT need a cotter pin.
 
I made an overdrive to go behind A 350 turbo in the 60's out of a chevy od trans
I had the input shaft tested for Rockwell hardness. Had it annealed cut the
shaft to length, turned the diameter to size, splined it & had it heat treated
back to 60 Rockwell. I ended up with a 4spd automatic with 2 kick downs.
It can be done
Rick Rentschler
Napa, Ca.
 
Aren't the gears pressed on ? hot gear/ cold axle -interference fit ? Shorten the gear end easier? Newc
 
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