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Thread: RUBBER, Versus POLY - The Saga Continues.

  1. #1
    Registered Member NickP's Avatar
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    RUBBER, Versus POLY - The Saga Continues.

    Argue here

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    I wouldn't think about using poly bump stops either. Squishy progressive bump stops work better, along with the rubber bushing adding some progressive spring rate over big bumps, or when it bottoms out, and the spring rate goes infinite, then something breaks. On smooth roads the rubber bushings offer very little rate to the spring. It might not help much, I don't know, but wouldn't the rubber bushing assist the spring in reverse motion, along with the shocks to keep the tire planted on bumpy roads? I've driven plenty of fast, great handling cars, on bumpy roads that felt well planted running on stock rubber suspension bushings. Not that the OE bushings can't fail, but I can't remember when I last had to replace one for a lot of years. I have had countless GM 4 link cars over the years, and they made some great ones. I think where people hinder the rear suspension action on those cars is when they switch all the rubber bushings over to poly, and use boxed control arms. They use an open channel on the stock links so they can twist too, when the rubber compresses so far in the bushing. Otherwise nothing can twist, binds up, spring rate goes sky high, and around she comes. Snap over steer is tough to drive out of. I still guessing of course, but with my imagination I could see that maybe Chevy went to the ugly, but effective composite small diameter dog bones, so they could twist and add compliance to the multi arc 5 link C4 suspension?
    I don't know this either, but I would think the 96 C4's had the best ride? And hell yeah, I would love to hear all about the dynamics, and functions of the C4 IRS. It seems like there is a lot going on back there with all the different arcs, changing wheelbase, camber, caster, toe, roll center, and even track width. Who knows what happens for sure, when you start changing components of the original design? Heim joints seem to be the obvious choice for trailing arms, since the OE bushing are not available. All that is needed is a good well made OE replacement, instead of some sales pitched, poorly made plastic bushing that almost fits. A modified, narrowed "well engineered and tested" IRS that worked better would be an amazing feat. Especially with the smaller suspension arcs, and a pro-stock narrowed track. I'm planning on a full roll cage for mine with a much wider track, with a cheap paint job on the roof until it can hit 1G in a corner on at least 3 wheels. I don't know what the effects are for, but I have read that GM made the axels (upper link) on the C4 IRS as long as possible for some stupid reason.
    Last edited by 55 Rescue Dog; 11-22-2016 at 03:59 PM.

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    I am reluctant to reply because of the shit storm that will go on, but here goes.

    Comparing the twisting action that has to go on in a 60s/70s GM coil spring/solid axle suspension to a C4 is comparing apples to oranges.

    The "Chevelle" suspension has significant twisting motion throughout its travel. The suspension arms are a "hat section" and have little torsional rigidity. When you box them, the torsional rigidity increases probably ten-fold. Add in pu bushings that are stiffer than stock, and you have a recipe for binding - and probably eventually breaking something.

    In constrast, while the C4 "dog bones" are a solid cross section and they are pretty stiff, the dog bones are not required to twist anywhere near as much as the bars in the Chevelle suspension. So even with stiff dog bones the bushings don't have to give much in twist, and they should work fine.

    In making the decision on what to use, you need some good data on what the real difference in materials is. And that's not ever going to be clear.

    As for your comment on rubber vs. pu bump stops - yes, rubber is not a linear material when you compress, tension, or shear it. But neither is pu. The biggest difference is that the pu material you can buy commercially starts out harder. But don't think it's not "progressive".

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    I wonder how many of the great handling cars, supercars, or all out race cars use poly bushings? None would be my guess. It's cheap plastic garbage that sells well. If rubber bushings were cheaper to make, that is what the aftermarket would be trying to produce/sell, and that would be an improvement. No moving parts is where it's at.
    Last edited by 55 Rescue Dog; 11-23-2016 at 05:15 PM.

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    Interesting ad in the Danchuk catalog I got today, and what I've been trying to say about poly bushings in general.
    IMG_0450.JPG

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    Holy crap! $300 a set. From Danchuk, those performance guys, yeah right. I'll pass, they're a ripoff.

    Like with any material you might want to choose for some application on a performance car, you might want to find out what you're getting. Whether the Delrin is polymer or copolymer, and whether the material is virgin, annealed, or double annealed, as well as whether there are any "alloying" materials in it. You might even ask if it's really Delrin (a Dupont brand) or some other acetyl.

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    Registered Member NickP's Avatar
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    BTW and FIY, this product is actually a RideTech™ component. Having said that, it's still worthy of the same questions Rick.

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    Looking at the at NP's drawing it looks like the dog bones create a pretty tight arc affecting the wheelbase lengths, which would also make poly bushings on the camber links a terrible idea too, since they have to move up/down, and for/aft all at the same time. The only things I see in the rear C4 IRS that wouldn't cause a bind issue using poly, is the batwing, and torque arm bushings. Driving the car easy cruising, the poly bushing probably feel great, but when the car is pushed to it's limits, it will bind up like a knot.
    Last edited by 55 Rescue Dog; 11-26-2016 at 02:39 PM.

  9. #9
    Registered Member NickP's Avatar
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    Quote Originally Posted by 55 Rescue Dog View Post
    Looking at the at NP's drawing it looks like the dog bones create a pretty tight arc affecting the wheelbase lengths, which would also make poly bushings on the camber links a terrible idea too, since they have to move up/down, and for/aft all at the time. The only things I see in the rear C4 IRS that wouldn't cause a bind issue using poly, is the batwing, and torque arm bushings.
    Whaaaaaaaat?

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    The suspension arms do not stay at a 90 degree angle to the mounting bolt through the suspension travel.Rubber bushings have enough give to not create a bind condition at the limits of the travel .There are companies that make heim jointed arms for c4 rear suspension .

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