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Thread: Lower Control arm bolt comes loose

  1. #11
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    I think Chevynut's comments on the length of the bushing and sleeve are pretty much what's going on.

    If the maker of the pu bushing just mimics the rubber bushing it's not going to do the job very well. If you want a bushing setup that's free to rotate, the Delrin/aluminum bushings may make more sense for a lot of applications.

    I have seen the shaft end bolt work loose on a tubular control that had poly bushings. But those were not even close to the style of stock bushings. There didn't seem to be much that could be done other than Loctite and torque.

  2. #12
    Registered Member NickP's Avatar
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    Quote Originally Posted by Rick_L View Post
    I think Chevynut's comments on the length of the bushing and sleeve are pretty much what's going on.

    If the maker of the pu bushing just mimics the rubber bushing it's not going to do the job very well. If you want a bushing setup that's free to rotate, the Delrin/aluminum bushings may make more sense for a lot of applications.

    I have seen the shaft end bolt work loose on a tubular control that had poly bushings. But those were not even close to the style of stock bushings. There didn't seem to be much that could be done other than Loctite and torque.
    Maybe safety wire them.


  3. #13
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    I've heard good and bad about PST, that's what brand bushings mine are, from about 25 years ago. For all I know, the bushing may have slid right in and I didn't know any better back then. Anyway I forgot that when I got new uppers with rubber, I was going to change the lowers to rubber but I forgot all about that. So new rubber bushings are in order.
    I may or may not reply for a couple days, taking a short time off to see my sister 5 or so hours away. She needs help getting her house ready to sell and she is giving me some nice tools her ex left that are "in her way". Sounds like enough to pack my cargo van.
    Tony

    1955 Bel Air Sport Coupe

  4. #14
    Registered Member chevynut's Avatar
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    If you want a free-moving front end to lift and shift weight better the poly bushings are better than rubber. Notice they have serrations on the end of the sleeves just like the stock rubber ones. The shaft, sleeve, and washer are all supposed to be held solid to the frame with no rotation. The bushing is supposed to rotate around the sleeve, but be locked into the shell in the a-arm so it doesn't rotate in the shell. Rubber ones are bonded to the shell and sleeve, and they restrict motion and "bind" when the suspension moves. That's why you have to tighten them with the car at ride height. The aluminim/Delrin ones are probably just as good or better as far as allowing motion, but they will give even a harsher ride since they don't absorb or isolate any NVH.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


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    56 Chevy 2-door BelAir sedan
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  5. #15
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    Mostly right on, but rubber does not bind. It can easily twist a few degrees under load, adding just a few pounds of progressive spring rate, which is why billions, and all production cars use them, and probably always will. They just plain work. In a race car, anything can be made to work, but it will never be smoother, or quieter than rubber. I don't know what the fastest current production cars currently use, but I would assume it is probably just a very well engineered rubber bushing.

  6. #16
    Registered Member chevynut's Avatar
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    Rubber bushings acts like a spring, and as soon as it moves away from a neutral position the rubber is in shear and resists motion. Call that anything you want, but I call it a bind that gets worse the further you move it. It doesn't allow the suspension to act freely. The reason production cars use them is because rubber is cheap, and OEMs are concerned about isolating NVH which is better with rubber. But rubber has poorer performance characteristics due to its softness which allows things to move around and go out of alignment if enough force is applied. It's just a well-known fact of material choices and tradeoffs.
    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

  7. #17
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    There have been so many people that have totally fucked up their rear 4-link GM suspensions by replacing the rubber bushings, and flexible control arms, with something hard. It has to be compliant to work as designed. I would love to know which state of the art performance production car uses poly bushings? The last time I looked, OE bonded rubber bushings are way more expensive than plastic ones, if you can even replace them. Usually you have to buy the whole assembly, which you might not even be able to buy. Then alternate bushings make good sense. If poly bushings are so perfect, why is that not the standard? There is so much to the story than NVH.

  8. #18
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    Here's something to think about. Rubber can be made in many degrees of hardness. The rubber in a suspension bushing would be measured in Shore A hardness.

    Polyurethane can also be made in many degrees of hardness. The bushings on the market are probably only a little harder than the typical rubber ones. Thing is, if they are pour molded, it can be hard to control. Why are all the aftermarket bushings polyurethane? Because it's cheap to do. A harder rubber bushing would probably be better if made right. But it would cost more, and it's probably not a viable product to sell because of cost. If you want the bushing free, then use the Delrin/aluminum bushings. They will be free and predictable, and will have less deflection. PU bushings not so much.

    The torque resistance offered by a rubber bushing is negligible and doesn't really contribute to spring rate of the suspension.

    Then there's the typical polyurethane disintegration problem.
    Last edited by Rick_L; 07-05-2018 at 05:20 PM.

  9. #19
    Registered Member chevynut's Avatar
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    You seem to have a mistaken impression of Polyurethane. Poly isn't "hard", it's typically harder than rubber and different Poly compounds are used to get different durometers for different applications. It's not rigid like hard "plastic" as you seem to think and it's relatively compliant so it can absorb some (quite a bit of) misalignment. You can't seem to understand that FACT.

    I don't see how you can "fuck up" a GM suspension with poly bushings if installed correctly. And who the hell uses "flexible control arms"?

    Rubber is used by OEMs due to its noise reduction and softer ride that some people want in a new car. Poly has been proven for decades and in millions and millions of applications as a performance improvement. If it didn't work, there wouldn't be so many companies offering it and motorists enthusiastically accepting it. Most people see it as an "upgrade" to their stock rubber bushings that tear and crack.


    "The main advantage of a bushing, as compared to a solid connection, is less noise and vibration are transmitted. Another advantage is that they require little to no lubrication. Disadvantages include:

    • Rubber bushings can deteriorate quickly in the presence of oils (e.g., motor oil, mineral oil) and extreme heat and cold.
    • The flexibility of rubber also introduces an element of play in the suspension system. This may result in camber, caster, or toe changes in the wheels of the vehicle during high-load conditions (cornering and braking), adversely affecting the vehicle's handling. For this reason, a popular aftermarket performance upgrade is the replacement of rubber suspension bushings with bushings made of more rigid materials, such as polyurethane. Polyurethane bushings are also available for many vehicles with approximately the same characteristics[citation needed] as the manufacturers original bushings, but with greatly increased durability.[citation needed] This is useful on vehicles that have a reputation for wearing out standard rubber bushings, but for which harder bushings with increased harshness of ride are not wanted."
    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

  10. #20
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    Whatever. I would love to test drive a C7 and see how sloppy the suspension is. And, if you look at how the ancient GM 4-link rear articulates you would see everything needs to twist, and move in multiple directions. My 13 Tahoe PPV even still uses that basic design. If you tighten it up with stiff bushings, and rigid control arms, it will BIND! And that's a fact Jack. If you have oil and grease all over your suspension bushings, then poly would be a great choice.
    Last edited by 55 Rescue Dog; 07-06-2018 at 04:42 PM.

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