I had head about this issue in another context in the 2000’s in an EAA seminar at Air Venture. I found an article that summarizes it and the basic issues are what I am taking about.
https://www.aviationpros.com/home/article/10383342/hanging-by-a-thread
I think that the axle spindles on a car are one of those items that are Safety Critical and should get much different attention than most of the other stuff the cars.
Yes, 98% of the time one can get away with not worrying about it. I just do not want to be in that unlucky 2% and have something fail and loose control and kill a carload of kids coming the other way.
James
From: John Nowosacki <jsnowosacki@xxxxxxxxx>
Sent: Tuesday, December 5, 2023 10:02
To: John Grady <jkg@xxxxxxxxxxxxxxxxx>
Cc: James Douglas <jdd@xxxxxxxxxx>; Bob Merritt <Bob@xxxxxxxxxxxxx>; Chrysler 300 Club International <chrysler-300-club-international@xxxxxxxxxxxxxxxx>
Subject: Re: {Chrysler 300} Chrysler Castle Axle Nuts - Correct Size - Finding
Evidence there is indeed a God-
A high school friend with an old Dodge boogered up the threads on his right rear axle after doing the brakes by cross threading the nut back on. He wound up using a stillson wrench and a length of pipe to
get the nut within about 2-1/2 washer widths away from the drum (basically cutting new threads on the shaft), and then put three washers on the axle up against the drum after backing off the cross threaded nut, and reinstalled said nut as tight as he could
get it with the three washers, knowing he was able to turn the nut to within 2-1/2! He drove that car for the rest of his high school years and for a number of years after that as well. Nothing ever came apart, vibrated, shimmied, or anything else. Ah,
the teen years.
Of course, he also had a habit of running worn out, recapped snow tires front and back on his car because he could get them for free from behind the Shell station off the 'take off' pile in the next town where
another buddy worked nights. Yikes!
Hi James -----Millions and millions are just screwed on and reused with zero issues. Sort of the reality.It may reduce safety factor some minor % theoretically but width of axle key area in circumference is small compared to rest of engagement
area, and allowed for already, probably why tall nut. Same discussion we had about the front suspension bolt. It is designed to be like that. Tall nut is how.
As far as "less engagement at tip" as you describe it, are you aware that American Standard threads were designed by a genius names Sellers, (as opposed to the then world standard mid 1800'sBritish Whitworth) for the reason that not only
different angle (60 degrees ) (W was 55) ,giving an easier thing to actually measure and possibly better stress , but very important, the tip of the male thread was changed from a close fit rounded tip it (Whitworth , rounded tip) to a flat face at tip (sharp
tip removed on purpose) with a space left on purpose where it would be, so easier to start on correctly, Far less susceptible to accidental damage to outer tip--that missing tip has no real impact (within reason) to achieved strength or anything else,such
as torque to achieve rated clamp forces. Junk in Whitworth=hard to turn. Galling etc . Torque not directly causing clamp, you do not know if fouled
I agree animalism is unlimited but unless unbelievably gouged or turned down deeply all 360 , I don't think there is any worry about the mechanism you are concerned with. If you can torque it to rating it is there forever, clamp force
intact , unlike ? less engagement of axial length. No need to clean up very much even , if it goes on reasonably with a wrench ----due to Mr Sellers. Think about it -----even if tips are mangled or missing with his design the forces are still intact at root
and essentially the same (tip fit or not) at the thick part of the thread cross section near bulk metal.
So going on loose (?) or tight being not very relevant was part of his insight . Add in tolerances.....Guy was a genius. 90 patents in machine tools.
Within a very few years his patent thread profile took over the whole USA manufacturing business. Of course , British did The British Thing. Sealing wax is fine, have to get mix right color.
John,
Everything you said is correct. But you are operating from an incorrect assumption.
When idiots take off the drums and allow the key to destroy the threads on the axle shaft. One can use a cleaning die or a file and take care of that. Thread engagement will be
lessened by the section that was destroyed and that causes a reduction in clamping force.
The big problem is that the same idiots that mangled the threads on the shafts also tend to put the nut back on and run them down over the damaged shaft threads that they had not
bothered to take care of . In the process they destroy the nut threads. Even if you can get a cleaning tap through the nut most of the time the nut is shot. Too much material is gone, and it goes on very loose and is a danger as its grip is severely reduced.
So, which god does one prey to?
A axle shaft that has reduced threads and cleaned up somewhat can use:
-
A old nut that has been run through with a tap and the thread engagement is very low across the entire thread range.
-
A new castle nut with a much smaller bearing on the washer, even with the stock nut the washers shows signs of cupper under pressure which would be worse with a smaller OD nut.
-
A heavy hex nut that has the factory bearing (OD) on the washer, but must be cut down to get on the “castle cap” to get the cotter pin in.
A new heavy hex nut would have more thread DEPTH on each thread than and old nut that had to be tapped and as such would have more holding power than the stock unit I think---but
I do not know. That question that would take a lot of actual calculations is which one in the end would hold more.
James
Hi
From from an engineering perspective, a nut that is somewhat mangled by normal abuse is plenty strong enough on this application, and more important has been specified in terms
of hardness, ductility, heat treat , resistance to shock, temp changes, length of thread engagement, thread loading at ft/Lb etc to do that job. A very hard ,high psi hardened nut may crack from shock loads or something,----hardening to high psi reduces
ductility... and that nut was a compromise of all this, well proven, by 25 +years of use. Safety factor is huge just looking at it, more likely it is that big ,to allow developing the axial force at a torque to seat taper fully, --not to "hold drum on" so
much.. Your old nuts are fine , NOT new ones with thick washer, due to resulting less thread engagement --the limited distance to cotter hole wasted under a washer hole.
With a washer it reduces thread length engaged with male end of the axle, a very bad idea. It is tall now to load the available threads a certain way, without deformation, fewer
threads leads to failure. The way this joint would most probably fail is a crack at the root of first inner male thread , breaking off the end of axle, not nut failing.. That is because fewer threads are distributing the same load, less threads working you
cause a stress riser at root of first thread, or even worse stretch it to yield with too much thread load. Then one day it snaps off on its own. I would not worry about the aesthetics of lug holding nuts. Why?
PS look at ARP site for more tech info. Especially around "toughness" or ductility. But old nuts are best.
Well,
I have spent days and could not find nut that has the rather large OD as the factory Castle Nut. They just do not exist.
One could order a Heavy Hex Nut and use one of those cotter pin toppers with it I suppose. The problem is that a heavy hex nut is also taller. It would have to be put into a lathe
and cut down.
Yes, I can find other used ones. But most of them have been battered by the pushed down threads of badly removed drum keys.
So much fun.
James
Thanks Zach, I have some used spares from my 1940’s Desoto’s. I was looking for some new nuts. Why? Because over time people pull off the hubs without giving the square pin a hit
on the end with a hammer and punch to make sure that then they pull the hub off it does not come with it. When it does come with the hub that destroys the threads on the axle shaft.
Idiots then do not case the axle shaft threads with a cleaning die and just stick the nut on and crank it down. That screws up the nut threads and they are never the same again.
If you chase the nut and chase the axle shaft you get a sloppy nut that will not torque correctly. Hence, why I am looking for new nuts.
I suspect that I am looking for a ghost and will have to just use the new nuts available and have to machine a washer to make up for the flange area and depth of the nut. In any
case a close inspection of the washers show that they are “cupping” a bit which means that the drum is pushing back on that nut. A hardened slightly thicker washer may not be a bad thing, I just hate to lose even 4 or 5 threads of depth with the available
new nuts. A VERY high-quality cotter pin is a good idea on these very old threads.
James
From: Zach Hietsch <zhietsch@xxxxxxxxx>
Sent: Friday, December 1, 2023 07:24
To: James Douglas <jdd@xxxxxxxxxx>
Subject: Re: {Chrysler 300} Chrysler Castle Axle Nuts - Correct Size - Finding
Hello James,
I have a 300B and I’m pretty sure I have a few spare castle nuts for the spindle to hold the drums on. Is that what you are looking for?
If it’s for the suspension I might have those too. I got a bunch of parts when I got my car and I haven’t gotten through all of it yet. There is also potential that they are not
for a Chrysler as my grandfather kept everything from everything.
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