Has anyone shortened a rear axle shaft?

[alchemy]

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.

[Kube]

Originally Posted by alchemy

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.

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.

[kurt v]

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.

[Kube]

Originally Posted by kurt v

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.

Per my previous post, that's the way I'd do it IF I had no source for a correct axle.

[tubman]

Here's related question. Could a good machine shop make a good '40 axle out of a "bunged up" later one?

[Krylon32]

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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

[tubman]

I was just asking out of idle curiosity.

[alchemy]

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.

[38 coupe]

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.

[SoCalCoupe]

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.

[Krylon32]

alchemy: Loosen that wallet, you can't take it with you.

[ford38v8]

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?

[V8COOPMAN]

Originally Posted by ford38v8

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?

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

.

[cas3]

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

[Pete]

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.

[convert 40]

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.

[Newc]

Aren't the gears pressed on ? hot gear/ cold axle -interference fit ? Shorten the gear end easier? Newc

[richard crow]

axle key not needed BULL S..T

[19Fordy]

For the amount of work, time and money it would cost you to weld up your own version of the axle you are better off just stepping up to the plate and buying a good one. This one is for sale at a cost of $3 per year storage.
https://www.ebay.com/itm/12596292073...4db3a439552906

[v8nut]

Check with ALL FORD in Campbell CA. (San Jose). They have a LOT of axles.

[big job]

What I gather you want to shorten it only .850 no problem all you need is a lathe. I believe the spider gear and shaft OD, taper, and thread is the same on 1940 to 1948 I think If so, you have all the measurements. Order of operations: #1 cut .850 from the threaded end & machine .850 thread size to the taper and pick up the thread pitch and re thread re drill for the cotter pin thats done. now machine the taper .850 longer re-machine the shaft for outer bearing. Now the key way. easy and fast is a milling machine or a shaper. any shop can cut a key way. This is exactly how we machine marine prop shafts same thing. hope I said this correctly for my brain to transpose into typing kind of like explaining how to tie shoe laces LOL sam

[Bored&Stroked]

While a competent machine shop should be able to accomplish the task, it would be much cheaper to just find the right axle.

[Mart]

It can be done and has been done. I broke a shaft in my 41 pickup (same as a 40) and was able to obtain one that was a shortened 46-48 shaft. It was not quite right and I skimmed the taper a little more to position the drum correctly.

I didn't do the initial machining but was able to take a light cut. I made sure the hub was well lapped to the axle afterwards.

I don't believe any heat treatment was carried out. The metal is tough and needs good quality tipped tools.

My axle had been welded at the mid point and snapped.

I showed it in a video mini-series.

part 1: https://youtu.be/t0AfzS5OLYE
part 2: https://youtu.be/i26ZSqwFIF0
part 3: https://youtu.be/8ToEl7O01P0
part 4: https://youtu.be/MOVxQP0aZhg

Mart.


Mart.

[deuce_roadster]

Just get a correct good appearing used axle and have it magged at the inner end of the keyway. A used axle with no cracks can be lapped to your hub. By FAR the cheapest solution.

[19Fordy]

Bored&Stroked got it right. Machine shop work these days is not cheap.

[Ricosan]

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Alchemy, there is a detailed video doing this online at Iron Trap garage. Lots of other videos at this site too.
Richard

[alchemy]

Rico, I can’t find the video you are talking about. Can you post a link?

Mart, I watched your videos and it looks like exactly what I want to do. Can you tell me any more info about the process, or if there was any heat treat in the axle?

Pete, can you elaborate on the process you used? Just a lathe and no grinder? You didn’t have chatter problems as you cut into the hardened surface (if it IS heat treated)?

[Pete]

Originally Posted by alchemy

Pete, can you elaborate on the process you used? Just a lathe and no grinder? You didn’t have chatter problems as you cut into the hardened surface (if it IS heat treated)?

It is heat treated. I used ceramic tool bit (carbide works also) and fairly high spindle speed. No grinder. Probably machined 30 to 40 finish and then lapped from there.

The splined late model axles were cut in the middle and welded to shorten for an econo blown Olds powered dragster. Around 400 hp. Only required 3 for all season. (broke one)

[Ricosan]

Alchemy, google “Iron trap garage”. Then click on “videos”
Richard

[Yoyodyne]

I'm discussing this with a friend, we'd like to do some calculations. Does anyone have the dimensions of the Ford taper handy? I'm looking for the large end diameter, the small end diameter and the length of the taper. The angle would be nice too, but we can calculate that from the above dimensions.


What thread is in the axle nut? And what is the factory recommended torque?



Unfortunately the only axles I have are in my truck.




BTW, I've seen axles successfully shortened by cutting extra long ones, or 2 axles, so that they can be sectioned together in sort of a broomhandle break fashion. That way the weld is not 360° around the axle, it also runs along the length. This way you don't have the embrittlement all around the axle in a circle and the weld is not all in shear. 3" section has always worked.

[Mart]

Threads are 5/8 -18 SAE UNF.

I believe the taper is 7 degrees. In my video I mention that it is an 8:1 ratio. You reduce the diameter by 1/8 of the dimension you want to shorten by.

It is tricky to measure a taper. You need to make sure you are measuring at the same place along the shaft. I tried to show some of this in my videos.

YOU MUST DOUBLE CHECK ALL INFO FOR YOURSELF. Do not take my numbers as gospel.

Mart.

[Yoyodyne]

Thank you Mart. I determined long ago that the tie rod end tapers are 1.5" per foot, which matches your 1/8 per inch figure. So there's a real good chance the axles are measured the same way. That taper is used a lot in automotive, or at least older automotive. 7° is very close to that.


Do you have a figure for the axle diameter at the big end of the brake drum taper or how long the taper contact is?

[alchemy]

The goofy part of measuring the taper is that it rounds off as it meets the full diameter of the shaft. You will need to determine a different point to cut to. I’m guessing you pick a certain diameter near the fat end, then a certain diameter near the skinny end. Then measure between to confirm? Or are there machinists gauges with a perfect circle that could be used?

I think some weekend soon I’ll just make a trip out to my buddy’s shop and show him what I’m thinking about. He likes a challenge.

Rico: I looked through every single Iron Trap video on YouTube and couldn’t find one pertaining to shortening an axle. Quite a few on how he shortens a drive shaft, but I must be too dense to find the axle video.

[Pete]

https://www.engineersedge.com/hardwa...sign_15009.htm

[Mart]

Originally Posted by Yoyodyne

Do you have a figure for the axle diameter at the big end of the brake drum taper or how long the taper contact is?

No. But the shaft you have has all the right dimensions. You just need to move them all along the shaft by whatever the difference is between a 40 shaft and a 48. (years quoted just as a example.

In my video I described where I used a bearing race to hold the calipers at a specific point and got a reference dimension. I was able to then measure the oversize shaft at the same point relative to the housing and work out how much over size it was.

My point is that you need to work things out for yourself based on the established principles.

Mart.

[Yoyodyne]

Thanks, but I'm trying to do some engineering calculations on paper, I don't have an axle in hand.