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Old 03-29-2020, 09:22 PM   #1
skidmarks
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Default Cutting down 42 to 48 ford axles for a 40 ford

Has anyone had success in cutting down the later 42 to 48 axles to use in a 37 to 40 rear?

Laying them side by side it looks to be enough material unless im missing something.

I got a pile of the later axles but ran out of useable earlier one. Most of the damage is to threads.

Would be a great use for the pile i got to end up with fresh taper.threads and keyways
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Old 03-29-2020, 09:36 PM   #2
richard crow
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Default Re: Cutting down 42 to 48 ford axles for a 40 ford

it,s much cheaper to buy a 40 axle than the work required ti shorten your axle .i have five early fords over 30 years & rotate driving them i have never broke an axle how maney do you think you will brake. are you into raceing are your cars souped up. if your axles are braking from normal use you should take a close look at the housing race,s if worn it can cause axle brakage
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Old 03-29-2020, 09:57 PM   #3
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Default Re: Cutting down 42 to 48 ford axles for a 40 ford

i was gonna do it once, but quit the idea. never could get the exact degree, i think its 7, and also i never get a nice cut when turning the compound by hand. had a cnc guy but he wanted a blue print. as stated, just by some nos ones from southside obsolete. lawrie down under did it i believe
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Old 03-29-2020, 11:05 PM   #4
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Default Re: Cutting down 42 to 48 ford axles for a 40 ford

Agree with all the above responses; as a machinist, I can tell you that machining a taper is very difficult.
Thing is once you've matched up perfectly the exact taper, next thing is to position it perfectly.
I am away from my logarithm tables at present, but if you calculate the sine/cosine/tangent numbers of the particular included angle of a Ford axle, you'll notice that for every, say one thousanth of an inch you remove from the taper, the longitudinal distance the mating taper will travel along said taper is , I dunno, maybe 12 thou?
Recently I rebuilt my diff using all NOS/NORS parts. I used NORS axles. One axle has the taper machined too small; it requires a shim in order to position the brakedrum in such a position it doesn't bottom out on backing plate.
Trust me, it'll be easier to locate correct axles for your application than attempt to shorten up longer axles.
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Old 03-30-2020, 05:57 AM   #5
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Default Re: Cutting down 42 to 48 ford axles for a 40 ford

With a taper attachment it shouldnt be a issue. Final fit, some blueing and some lapping compound would show the fit.

I know a phone call is all i need to do to buy a set. Im looking for information from someone who was successful in doing it.
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Old 03-30-2020, 06:18 AM   #6
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Default Re: Cutting down 42 to 48 ford axles for a 40 ford

I traded for one that had been modified. It was not quite right as far as the positioning of the drum so i set it up and skimmed a few thou off the taper. I then had to contend with a keyway that was not quite deep enough.

So it is possible to do the job. Things to note are:
The material is very tough. It needs a good insert tool to turn it.
You don't shorten it enough to lose the keyway. There will be remnants of keyway where the threads are.
The diameter of the taper at a specific distance from the gear is very important as it effects the position of the drum.
Milling the keyway can be tricky to set up as it is at an angle.

If doing one you might consider doing a batch all the same if the "prototype" checks out.

My series of videos from when I broke the shaft in my truck shows the shaft and the problems I had to overcome.

I think this is one that shows the axle.
https://youtu.be/8ToEl7O01P0

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Old 03-30-2020, 06:31 AM   #7
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Default Re: Cutting down 42 to 48 ford axles for a 40 ford

Thanks for the input,

Toughness of the material, hard as the wheel bearing surfaces?

Making the taper and key from scratch could be pretty challenging but having the original to work from and moving it up the axle a very short distance doesnt seam like too much of a challenge . The taper attachment once its set is doing all the work. I got about 25 axles that no one wants and all the equipment to preform the task. So nothing to loose


Quote:
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I traded for one that had been modified. It was not quite right as far as the positioning of the drum so i set it up and skimmed a few thou off the taper. I then had to contend with a keyway that was not quite deep enough.

So it is possible to do the job. Things to note are:
The material is very tough. It needs a good insert tool to turn it.
You don't shorten it enough to lose the keyway. There will be remnants of keyway where the threads are.
The diameter of the taper at a specific distance from the gear is very important as it effects the position of the drum.
Milling the keyway can be tricky to set up as it is at an angle.

If doing one you might consider doing a batch all the same if the "prototype" checks out.

My series of videos from when I broke the shaft in my truck shows the shaft and the problems I had to overcome.

I think this is one that shows the axle.
https://youtu.be/8ToEl7O01P0

Mart.
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Old 03-30-2020, 06:41 AM   #8
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Default Re: Cutting down 42 to 48 ford axles for a 40 ford

To be honest, Skid, I didn't find the material too tough, but I only took 5 thou approx off. It was a conversation with the person that supplied the shaft and he said the machinist that did the job said it was tough.

If you have that many axles it would be well worth setting up to machine them as they would be worth money to people that need them. Put it this way, here in the UK I couldn't find a proper 40 style and the modified one was the only option. The person that supplied it had them made because the others are in short supply.

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Old 03-30-2020, 06:51 AM   #9
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Default Re: Cutting down 42 to 48 ford axles for a 40 ford

The biggest issue i keep running into is the damaged and chewed up threads. Some have some issues on the taper that could be dressed up .
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Old 03-30-2020, 08:08 AM   #10
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Default Re: Cutting down 42 to 48 ford axles for a 40 ford

Good reason to change the rear end to a later open drive unit. I gave up on these rears and trans 50 years ago. If your a puris fine, but a daily driver, not so much.
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Old 03-30-2020, 09:41 AM   #11
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Default Re: Cutting down 42 to 48 ford axles for a 40 ford

I have shortened dozens of axles by cutting and welding. Of course straightening after welding.
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Old 03-30-2020, 02:42 PM   #12
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Default Re: Cutting down 42 to 48 ford axles for a 40 ford

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Good reason to change the rear end to a later open drive unit. I gave up on these rears and trans 50 years ago. If your a puris fine, but a daily driver, not so much.

I'm with Ol' Ron' thinking, except I would not go to a later model open drive line.
My '36 originally had a Columbia under it when I bought the car in '52. Did not like the antiquated controls so I upgraded to a '42-48 Columbia. I used the '36 center section/drive line, 47-48 axles/housings, '47-48 Columbia, '37-38 radius bars (correct length, fit) '39 drums. A bolt together modification.

The '42-48 rear end is slightly under 2" wider than the '36, however, that equates to less than a 1" on each side which does not worth the added work to shorten the axles.
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Old 03-30-2020, 06:31 PM   #13
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Default Re: Cutting down 42 to 48 ford axles for a 40 ford

With respect to all the good suggestions, I think I would be looking to weld up the thread then grind it /turn it in a lath then re thread it, you may need to heat treat it before and after .As temporary measure after tidying up the thread the best I could with a adjustable die nut, I then used a 5/8 unf nut and slit it with a hake saw squeezed it up on the axle then welded up the cut, it worked well . From the Model A venders there's a nut that does this .do a search on the A site
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Old 03-30-2020, 09:01 PM   #14
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Default Re: Cutting down 42 to 48 ford axles for a 40 ford

If the only problem is the threads, that is easy to fix by TIG welding with ALLOY rod and
re-threading. No further heat treat is needed.
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Old 03-30-2020, 09:34 PM   #15
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Default Re: Cutting down 42 to 48 ford axles for a 40 ford

I turned some 46 axles down in the lathe to fit the narrowed up 39 rear end we used in our dragster,did lots of passes and half na season with the blown engine,never a problem.so to machine some later ones down to fit our 33 would be no drama. But they are very hard and tough
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Old 03-30-2020, 09:53 PM   #16
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Default Re: Cutting down 42 to 48 ford axles for a 40 ford

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I turned some 46 axles down in the lathe to fit the narrowed up 39 rear end we used in our dragster,did lots of passes and half na season with the blown engine,never a problem.so to machine some later ones down to fit our 33 would be no drama. But they are very hard and tough
Lawrie

Thats what im going to do. when im done i got a fresh taper, keyway and threads
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Old 03-30-2020, 10:13 PM   #17
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Default Re: Cutting down 42 to 48 ford axles for a 40 ford

Good call Pete ,I questioned that ,
Lawries done it ,your the man .
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If the only problem is the threads, that is easy to fix by TIG welding with ALLOY rod and
re-threading. No further heat treat is needed.
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Old 05-07-2020, 10:54 AM   #18
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Default Re: Cutting down 42 to 48 ford axles for a 40 ford

Both axles machined with no issues. So now i got 2 with fresh tapers and key ways. Just have to trim off the excess threads. Shown as a comparison how much was turned down to fit a 40 rear.

With a taper attachment the lathe does all the work. Set up time on a face plate is simple.
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Old 05-07-2020, 11:13 AM   #19
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Default Re: Cutting down 42 to 48 ford axles for a 40 ford

My fading and poor memory suggests that rumbleseat addressed this for his 34. My recollection is that he used a 46-48 columbia, and whatever he did to the axles was 'trivial'. Someone here can probably elaborate, and perhaps post his notes on the subject.
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Old 05-07-2020, 12:39 PM   #20
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Default Re: Cutting down 42 to 48 ford axles for a 40 ford

Excellent job, Mr Marks. A taper attachment is something I do not have. I had to do mine with the compound slide. Glad I was only skimming, not making from scratch.
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