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Old 10-22-2007, 10:37 PM
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Thinking about building a custom straight axle front suspension

I am thinking about building a custom front axle for my street rod, and just wanted to run my thoughts by some of you who have actual experience with straight axle front ends. Here's what I have in mind
  • I have a pair of GM G-body (Monte, Regal, Cutlass, Prix) front knuckles (complete with rotors, bearings, and calipers) that I plan to have line-bored through the tapered ball joint holes to accept bronze sleeves.
  • The axle itself would be a dropped configuration, fabricated from sheetmetal, with sleeved tubular ends designed to mount the G-body knuckles, with a long bolt.
  • The bolt would be the strongest hardest sucker I can find, with a nylon insert lock nut on the bottom; and a pin or saftey wire for extra peace of mind.
  • The axle would be mounted with really short, dual, semi-ellipitical leafs; with custom frame rails that arch over the axle.
  • The front spring mount, on each side, would be a pocket inside the frame rail; and leaf sliders for the rear mounts (instead of shackles - cleaner)
  • I am also thinking about adjustable blocks between the spring and axle for precise alignments.

Why go through all this? I get relatively modern brakes and bearings, and a really trick front suspension hanging out in front of the truck, and the satisfaction of saying "I did it my way".

Thoughts?

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Old 10-23-2007, 07:37 AM
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Some drawings or sketches might help here to visualize what you have in mind. But if I understand you right (which I probably don't - not enough coffee yet this morning), it seems to me what you have here is a "twin beams" setup (I think Flaming River now makes something like this). But due to the short length of your axles, I think you are going to end up with some real camber problems and some bump steer issues as well. The Flaming River axles are half the width of the front track (they meet in the center) and the old Ford twin beam set ups have overlapping axles - to get even more travel radius and reduce camber fluctuation.

Again, a sketch would help. But I think what you are trying to do will get very dicey in terms of geometry.

Dewey
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Old 10-23-2007, 01:21 PM
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Sorry this is so generic - I didn't have a lot of time to put in it.

It would be a solid straight axle, not twin-beam independent. I would love to have independent but my plans are much to narrow for that; and the camber curve would be crazy - just as you mentioned. I owned some Ford twin I beam trucks before, and am aware of that style. For how I plan to use this project, I don't think it would be worth the extra engineering hassle to do that, even if the geometry was decent.

I just did a simple tube shape for the axle in the model, because of the time issue; but I am really thinking more along the lines of a fabricated axle. I was thinking about making it look like an I-beam with the vertical piece cut from 1/2-inch plate and the top and bottom horizontal pieces cut from 1/4-inch - all welded together. If the budget allows, I can have the 1/2-inch piece cut on a water jet with lightening holes...

Hope this helps make the idea a little clearer.

Last edited by toddshotrods; 10-23-2007 at 01:27 PM. Reason: wrong pic & typos
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Old 10-23-2007, 05:16 PM
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Quote:
Originally Posted by toddshotrods
Hope this helps make the idea a little clearer.
Yup.

I'm a huge fan of using existing parts to fashion novel setups, but in this case it sounds to me like the amount (and risk) of specialty fabrication work might outweigh the "did it myself" badge of courage. But if you're up for it...who's to argue.
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Old 10-23-2007, 05:23 PM
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Are you saying that you are going to mount the spindles with a long bolt instead of a king pin?
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Old 10-23-2007, 05:56 PM
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Quote:
Originally Posted by Henry Highrise
Are you saying that you are going to mount the spindles with a long bolt instead of a king pin?
I didn't elaborate on that because I wanted to see if it would draw attention to itself.

Yes, that's exactly what would have to be done. That is the one area of te deisgn that I am not sure of, and wanted more feedback on. There is not enough "meat" on the spindles (in the balljoint mounting areas) to bore them for relatively large diameter king pins. When I first realized this I started to just scrap the whole idea, but then I thought about how small the tapered shaft of the ball stud portion of the factory balljoints are. I decided to at least give the concept a serious once over.

Maybe a better option, over bronze sleeve bearings in the knuckles, might be to bore them for a press fit solid shaft. A bronze sleeve bearing (I.D. sized for the shaft) would still be in the axle to allow the knuckle to pivot freely, and without wear. The shaft could have a rounded head on top, and external retaining ring on the bottom.

Quote:
Originally Posted by cboy
I'm a huge fan of using existing parts to fashion novel setups, but in this case it sounds to me like the amount (and risk) of specialty fabrication work might outweigh the "did it myself" badge of courage. But if you're up for it...who's to argue.
Point taken. I am pushing myself there purposely. I'm more than up for the challenge, just want to mix in some experience-based wisdom from seasoned rodders.

I haven't decided whether or not I am going to do it yet - I don't have enough info yet. I can easily abort and go with fabricated tubular upper and lower arms but... I am going to do some research on the strength of the shaft next...

Last edited by toddshotrods; 10-23-2007 at 06:05 PM.
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Old 10-23-2007, 09:41 PM
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Custom straight axle front suspension

Mas will build you an axle to almost any configuration you want. Have it made to use '45 Chevy spindles. Then look at what Speedway has for modified spindles. I don't know about making an 'I' axle out of CRS.

Youngster
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Old 10-23-2007, 10:38 PM
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I've looked at the offerings of those companies countless times. Speedway's catalogs are normally close by when I am planning. Nice stuff, but just not what I am looking for.

CRS as in "Cold Rolled Steel"? I would be using 4130 Flat Stock; .250 and .500 thicknesses.

I could just model the axle and have it cut from 6061 or 7075 billet, but that runs up the cost and strays too far from the theme and method I chose. With the high-end fabricated axle, I'd have about $250 in materials, and about $350 in services (laser cutting, TIG welding, etc.). Of course, that' not counting my labor, but that's one of love.

Last edited by toddshotrods; 10-23-2007 at 11:51 PM. Reason: wrong info - typos
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Old 10-24-2007, 07:41 AM
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Mt first two reactions to your drawing are; The joints at the axle i-beam or tube to the up-right are high stress areas due to the length of the up-right and the design looks to be rather heavy, having a lot of unsprung weight. Additinal bracing would strengthen the joint areas, add even more to unsprung weight.
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Old 10-24-2007, 08:29 AM
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Quote:
Originally Posted by Dugg
Mt first two reactions to your drawing are; The joints at the axle i-beam or tube to the up-right are high stress areas due to the length of the up-right and the design looks to be rather heavy, having a lot of unsprung weight. Additinal bracing would strengthen the joint areas, add even more to unsprung weight.
In that design there would definitely be gussets to strengthen the joint of the axle and knuckle mounts. Probably .250" 4130 with a lightening hole in it. I didn't have time to do anything else to it, so there are plenty of issues in the first model.

While the design appears to be very heavy it should actually be in the same ballpark as a traditional aftermarket straight axle. A traditional axle has somewhere in the neighborhood of 300 square-inches of .250" wall steel. My fabricated I-beam design has about the same.

I hope it doesn't seem like I am trying to discount your points guys, because I am actually taking everything you have pointed out here into serious consideration. The counterpoints I bring out are merely my thoughts on the design; and are by no means considered to be more valid than your insight. I posted the idea here for it to be critiqued and possibly even ripped to shreds. I actually have a second generation design brewing in my noggin, that incorporates some very important changes, based on the discussion here and my personal thoughts on this.

Please keep it coming...

Last edited by toddshotrods; 10-24-2007 at 08:37 AM.
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