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Thread: Does using polyurethane bushings on a C4 rear suspension cause a major bind?

  1. #1
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    Does using polyurethane bushings on a C4 rear suspension cause a major bind?

    After trying to visualize all the different arcs the rear suspension arms have to move in, during bump travel, it seems like there would be a tremendous amount of binding/twisting forces applied to the anchor points, if you replaced the original compliant bushings, with poly bushings. It would be great if there was a available spherical bushing that could be pressed into one the pivoting ends of all 6 control arms. Newman had the right idea, but it could surely be done for less than $700, I would think.
    Last edited by 55 Rescue Dog; 03-12-2016 at 03:53 PM.

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    Doesn't Cnut build some of the links custom with spherical rod ends? Not sure what pieces you get for $700 from Newman, seems like if you could do your own you could save. No idea what Cnut charges, but it's probably somewhat reasonable. Some other commercial solution may or may not be as expensive.

  3. #3
    Registered Member chevynut's Avatar
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    How much "binding" is there over 2-3" of travel? Let's see some numbers.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


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    I can only comment on this from what my father knows about polyurethane from a manufacturing perspective (but what he says is corroborated by some pro-touring communities, and one Mary Pozzi who is no dummy). Polyurethane will ovalize over time (that is, it doesn't have the same properties as rubber) so, personally, I think it's a poor choice for any suspension component that needs to rotate/articulate/house anything that needs to maintain alignment on an axis that's subject to shock (which is the case with all control arm and leaf spring bushings). It's great for body mounts and sway bar bushings though. I honestly think they'll all squeak so I wouldn't even consider using them without a greasable zirk fitting.

    My pop has poly bushings on his 67 Vette...they squeak something fierce. He greases them every year or so and while that helps for about 3 months, the poly bushings push out the grease eventually and squeak again.

    I think delrin is where it's at for control arm and leaf spring bushings unless you want to go with rubber. Just my opinion. Delrin is more expensive, but it's a far superior material if you're not concerned about noise and vibration transfer. Delrin also doesn't wear out like rubber or poly so it's a one-time deal.

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    Unless the rear C4 spindle upright stays completely vertical during its 5 inches of travel, something has to give. Any change in camber, caster, or toe, is going to try to twist, and turn every bushing. Since the OEM rubber bushings can only be replaced with poly, it will no longer work as designed. I would think a poly bushing would be fine on one end of the locating links, if there was a spherical bearing available that could be pressed into the other end. Or, replaceable OEM bushings. The poly bushings are just to hard to work properly with an IRS, IMO.

  6. #6
    Registered Member chevynut's Avatar
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    Chad, I personally think Delrin is too hard for a suspension bushing for a street car. For racing it would be good. Polyurethane has been around for decades and millions of cars have used poly bushings. Your father's vette is probably squeaking in some place other than between the sleeves and poly, like where there's a washer over the end of the poly. That's why greasing them doesn't help much. As far as "ovalizing" most of these bushings are designed to be constrained between washers so if they're used correctly I don't see that happening. In fact, it's probably more likely to happen at the swaybar bushings that aren't as constrained. I use them on my pinion support. It's made of two bushings 1.25" OD and .75" ID so there's .25" of poly all around the sleeve. At the ends it's constrained by a bracket that compresses the poly. IMO it's not going anywhere. Most suspension bushings are designed similarly...or should be.

    Poly bushings improve the articulation of the suspension by allowing the inner sleeves to rotate in the bushings. Rubber bushings are molded solid to the outer case and the inner sleeve so the rubber has to flex. Eventually it will tear. Poly is soft enough to allow some misalignment too, as is rubber.

    There are no rubber replacement bushings for C4 suspensions, so poly is the common replacement that most people use. I think using steel bearings is ok for a race car, but they'd probably rattle your teeth on a street-driven car and they will eventually wear out causing alignment issues...not to mention the cost. And what's the point if polyurethane improves articulation? How much articulation do you need over a 2-3" up/down movement at the wheel? That's only a few degrees at the bushing. Small misalignment angles are easily accommodated with poly bushings. Put one in a dogbone end and move it side to side....it moves a bit. IMO polyurethane is a better choice than rubber or steel. I used polygraphite on my Nomad, greasng everything well, and time will tell how well it works.

    RD, you have it backwards. Any deflection of rubber or poly bushings is going to change camber, caster, or toe. Rubber deflects more than poly.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

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    It looks to me for example, if you had solid bushings in all the rear suspension links, and just camber gain alone would cause the dog bones to try and rotate lengthwise for one, and the suspension would be bound up. If the toe changes while turning that would make it bind some more.

  8. #8
    Registered Member chevynut's Avatar
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    "Some" is the key word. Nothing "binds up" with poly bushings. Go with the spherical bearings if that makes you sleep at night.
    Last edited by chevynut; 03-13-2016 at 01:54 PM.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  9. #9
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    The bushings appear to bind in this video, and they are not even loaded by weight or g forces.https://www.youtube.com/watch?v=6qgAXtVCauY
    Here is a good under car video of the C4 rear in action.
    https://www.youtube.com/watch?v=MhK5eKXC8Og
    Last edited by 55 Rescue Dog; 03-13-2016 at 02:53 PM.

  10. #10
    Registered Member destroyertta's Avatar
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    When I did the bushings on my Camaro I used polyurethane my friend suggested using powdered graphite instead of grease worked great I never heard it squeak I plan on doing the same when I do the bushings on my c4 parts

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