Thread: Wishbones and Tube Axle

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(I meant hairpins - jc)

Ok, here's the deal. I realize that wishbones are best used with I-beam axles because the I-beam will flex, and tube axles won't. My project (in the photo) is a Gibbon body on a P&J chassis. However, I bought it unfinished from Gibbon, and the tube and 'bones were already installed.

Based on my AutoCadd anallysis, if the right front wheel moves up 2.5" (over a bump) and the left does not move, about 0.200" of displacement needs to be taken up somewhere. One wishbone tube on each side is going to try to compress, and the other is going to try to stretch. If everything equalizes, each bar (less any twist in the axle) is going to have to take up about 0.100." Seems like a lot of pulling, pushing and twisting for good ol' steel.

Any odds on this thing falling apart in the first 500 miles? Opinions?

I guess I'll call Jason or Jerry Slover and ask them.

I'm no engineer. But I have an opininion (and just like everyone else I have one of those other things too). You said wishbones but it looks like hairpins to me. Hairpins have a little flex in them if they are not "bridged" together in the middle. Wishbones are traditionally mounted using truck tie rod ends and are quite rigid. Wishbones used to be mounted with spherical rod ends that are also quite rigid. More recently hairpins (and some split wishbones) have been mounted with rubber bushed ends. I think the combination of wishbones and rubber bushed ends should have enough give to work. Alan at Flatlanders in Newport VA (don't have the number right at hand) has been making and selling tube axles for years. Find the number and give him a call. I suspect he will tell you that your set up is OK.

Duh on me . . . ! They're certainly hairpins, not wishbones. Must've had a brief walkabout.

The hairpins have clevises at the batwings, and urethane bushed bar ends at the frame. They are not bridged.

I'm guessing that between the various flex points and the urethane, it will keep it from breaking.

Here's the response from P&J. Thought I'd pass it on . . .

Jack

Through our lab testing we have found that the tube axle flexes more than anyone in our industry ever imagined. Not as radical as an I-beam but it does flex non the less. We have also found that the hairpins vs. original solid wishbones carries a tremendous amount of flex. The taboo combination is tube axle and stock Ford wishbones. Although I have seen this done, but we do not recommend it.

Now back to your original question, this has been used in several vehicles in recent years. No stress related problems at all. So with lab tests, vehicle tests, and overall knowledge and experience with hairpins/4-BARS and tube axles our opinion this system is fine.

Thanks,

Jason