The Jalopy Journal
Discussion in 'Traditional Hot Rods' started by tinhunter, Dec 14, 2013.
Actually it was Frank Kurtis who first used the axle pivot in the mid 50s.
HRP...torsion bars and sway bars aren't tubes, they are solid shafts.
A tube axle with split 'bones will work on a light car, the whole car rocks instead of the axle twisting. Like a big sway bar.
Might want to rethink that.
I've seen a few failures caused by potholes (and ditches) with a stock style axle too.
Just looked at your project thread if it's a bellytank that running in a straight line over a relatively smooth surface it'll never matter ever
As usual, Always good info on this site.!
How about a ply.'wavey axle(it is a tube?)?
Would it have a problem w/ Not, flexing/twisting using 'split bones?
Is there any significance in the axle being wavey, ie: Allowing twist perhaps!? Or maybe just to clear parts of the vehicle it was designed for? Thank you
I'm wondering if the 'smile' in a Superbell tube allows a small amount of twist to occur? I would always agree that an I-beam works best with split 'bones, especially if they're anchored out on the chassis rails, but in this case maybe not a problem?
Same as with Chuckles0's case with the wavey Plymouth one? And '37 Ford tubes were an oval section, I think, and also curved, so again would allow some torsional flex.
Being as the truck as had a lot of miles on it with the tube it would appear as it might not be a big problem being as the wishbone is in near orig. position ( not split wide), however I guess my concern is that it may just let go at some point and being as I'm planning/doing a freshen up, I will be replacing it with an I beam..
I think what happens with a rigid tubular axle that is held by split wish bones is that the spring twists as one wheel goes over a bump. This also happens with an I beam axle but probably less because the axle is also able to twist.
You ever watch a front end guy bend an I beam axle for alignment? I had to walk away when they did my coupe. Just wondering if they can do the same to a tube axle?
Regarding the twisting tube axles I always understood this to be an issue twisting the axle through the welds where the cast or forged ends join the center tube. If the axle were truly a straight tube it would stress where and how the bones were mounted which could be minimal.
I think the answer to this on 35-40's with most or all 4 bar set-ups have no turning radius.
No one mentioned the 'cast' parts in the aftermarket business...cast perches....cast I beam axles, etc......what's the 'give & bend' characteristics here. There are some parts that do not need the forged steel material, but in my book....NO CAST parts......but, that's me. Robert
totally agree !
R Pope, remember when Jim Ewing brought out the Super Bell tube axle ? Pete & Jake's immediately produced their 4-bar setups, and both companies sold millions of each, partly because, together, you end up with a great handling frontend with no bind whatsoever. My '37 Ford has a tube with slightly-split "bones", and it rides like a fucking tank. It has been sold.
Dean Lowe, consider yourself one lucky individual. Lucky or not, you are fighting Physics, which will win in the long run. Good luck with your ill-designed car.
I know if you get the geometry of the front end correct , your car will drive much better, getting all the flex and bending outta the front end will be safer period . !
Thats a bit harsh....
Dean brings up some good points regarding split bones and a tube axle in that most times the suspension is only gonna see a small range of movement.
Combine that with some chassis flex, plus a lightweight vehicle and you will never see stress get to the point where failure will be a problem.
Now...go to a heavy vehicle with more of the weight over the front, combined with a stiffer X member frame AND the looser style spring ahead/panhard bar axle assembly (designed by Ford to have much more flex for ride), rather than preloaded shackles and you are likely gonna see a problem with fully split bones and a tube.
Gotta remember here, not everything is absolutely black or white in building cars...and by nature Hot Rodders operate in the shades of grey somewhere in between.
If you lay two straight edges or rods along side the bones and extended back a foot or so you will probably find out that they come real close to intersecting at the spot where the original bones rear mount was. That is what makes the setup work without a lot of issues that concern folks on tube axles with split bones.
Yep, I pretty much figured that..Thanks ..
I think it's spot on actually ... Bad advise is bad advise ... Telling someone it's not a problem when it is... Just because his hot rod hasn't had a problem is not sound advise... I have done all the things your "not supposed to do" but also weigh the risk and adjust the design based on application ... I have seen lots of failure because someone said " you'll be fine I did it on my car" I have used 36 ford rear bones many times on open drive rears.... But I have also seen them twisted like pretzels , rear housings with chunks busted out of them because of poor geometry ...
I have seen perches busted because of tube axles and bones ... These so called expert hotrod builders are no where to be found when you are broke down on the side of the road because of their advise
Speedway tube axle and others are just tube material with bungs welded in. You are relying 100% on the weld to hold up and IMO this is dangerous.
The stresses with a lightweight vehicle like a tub or roadster is not a big deal with this type axle. Especially street driven (pot holes excluded)...
Magnum, Superbell, Lucky 7 make tube axles with forged ends with a tube center. IMO much better design for the tube. (kind of a hybrid of sorts) Looks good and saves a couple pounds in comparison to a I beam type.
Either way the tube design is not as good from a "strength" point of view. You need a much larger cross sectional area of material to have the strength of an I beam in the cantilever mode. (tubes are for twisting and beams are for loading)
Two good things about the tube is aerodynamics and they are equally strong up and down and front to back, and strong in torsion.
I Beams are really designed for up and down loading and not so much for front to back.
One thing I never understood is that the most extreme loading (excluding potholes) is front to back loading from braking and acceleration. But understanding the dynamic stress applied to an axle under acceleration, deceleration, cornering, as well as cyclical loading is an intensive amount of calculations and experimentation.
So all said, I you are scared go get an "forged" I Beam. I never seen one break and they last forever.
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It was harsh...for the very reason you mention above.
It's fully conceivable that Frank Kurtis would "weigh the risk and adjust the design based on application" and there's no reason to think Dean wouldn't as well.
But this thread isn't really about Dean, Gary or Frank Kurtis...its about a nose heavy 40 pickup surviving with split bones and a tube axle.
Dean mentions his A R/pu with a tube and hairpin radius rods. Not really the same thing. Lighter vehicle with a more flexible mounting system and frame.
Gary has anything with a tube and a 2 point attachment written off...and thats not correct as there are ways to do that without causing undue stress. (Not all pretty, but thats not the point.)
Bottom line...when it comes to a heavy vehicle + stiff chassis + tube axle + wide split bones, we're all likely in agreement.
It's the absolute worst case senario for a pretty unforgiving suspension setup.
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