"A"Body 4 control arm

[joepenoso]

Assuming you have a 1971 "A"Body 4 control arm suspension............using stiffer control arms and poly and /or delrim bushings.........in order to prevent binding is it necessary to use both upper lower control arm "J" joints???
Could you get away with using rubber bushings in either or upper /lower control arms?
Thanks
joepenoso

[Vince@Meanstreets]

almost, you will get alot of unwanted movement if you use rubber.

are you on a budget or just curious?

[joepenoso]

Both budget and curious. I'm not sure how much difference rubber verses plastic bushing will affect rear end compression during turns.
joepenoso

[BMR Sales]

Remember with the the number of links involved, you don't want unintended movement. Rubber Bushing give a lot of movement, but they were installed by the factory because that was what was available & they were softer, so it gave a better ride.

Poly came along because they are stiffer, last longer & provide a more consistent precise movement.

Delrin is a step up from Poly as they are stronger & don't squeek as much

Spherical Bearings are Race oriented as they give razor sharp precision, but no comfort level

T.C.

[kevmurray]

Originally Posted by joepenoso

Assuming you have a 1971 "A"Body 4 control arm suspension............using stiffer control arms and poly and /or delrim bushings.........in order to prevent binding is it necessary to use both upper lower control arm "J" joints???
Could you get away with using rubber bushings in either or upper /lower control arms?
Thanks
joepenoso

The factory setup worked in what would be considered bind because both the bushings and arms gave. The compliance of the rubber bushings allowed twist and also absorbed some NVH. The factory arms would also twist a bit.

Once you go to rigid arms you really should go rubber or spherical. Rubber for comfort or spherical for precision. The Delrin in most spherical joints absorbs a little NVH, but rubber is king in that regard. Poly usually squeeks because of bind, not so much because of the material itself. Grease helps for a while until the twisting forces push it aside.

Consider how the upper arms angle in from the chassis to the axle ears. When the arms swing upwards the axle ends want to swing outwards, but they can't because the axle ears are a fixed distance apart. With rigid arms and rigid bushings this results in bind. Some people never have ussues with poly bushings but I wouldn't bother with them simply because they might squeek. I have Spohn arms that are all spherical - with the addition of a set of UMI Roto-joints. I had rubber in the axle ears with same arms before and didn't notice a difference in ride quality after replacing them with the UMI rotos (though the initial change to tubular arms with spherical joints was noticable).

Kevin Murray

[joepenoso]

Thanks Kevin for giving some real world experience.......
joepenoso

[BMR Sales]

I have to disagree with Kevin on a couple of points

"Once you go to rigid arms you really should go rubber or spherical. Rubber for comfort or spherical for precision. The Delrin in most spherical joints absorbs a little NVH, but rubber is king in that regard. Poly usually squeeks because of bind, not so much because of the material itself. Grease helps for a while until the twisting forces push it aside."

For Rigid Arms it would be Poly, Spherical or Rod Ends. Sure Rubber would give a more comfortable ride, but Rubber twists and initiates Bind. There are reason that no one in performance aftermarket parts uses Rubber. A properly greased Poly Bushing will not bind - squeeking comes from the Bushing being not lubricated & binding.

Delrin is a Hard Acetal Co-Polymer that needs to be milled and can be used as a Bushing when made out of the correct Grade Delrin. Spherical Bearings may or may not use a Poly Sleeve to absorb shock. Delrin being so hard would not do that

[kevmurray]

TC I agree that no performance car should use rubber. My post was intentionally brief and in hind sight a bit unclear. I think rubber bushings are good for comfort in a street car. When I said "rigid arms" I literally meant the arms, excluding the bushings. Unboxed factory arms deflected but modern tubular do not. This is why I recommended bushings that either give (rubber) or allow articulation outside of a plane (spherical).

I know of racers who have had success with poly bushings but in my opinion spherical is better in this regard. Heim joints are fine for racing but roto and johnny joints have a little more NVH reduction because of the Delrin. Key word being "little." They also last longer than heims and can be tightened and rebuilt. I have heard of some with a poly isolation layer but who offers them escapes me.

On the cause of bind I respectfully disagree with you. Bind occurs when a suspension member does not track the arc dictated by it's bushing. Bind is what causes a bushing to twist, not the other way around. Any sort of spherical bushing allows its member to travel outside of a plane. Rubber and poly do also, but do so through distortion of the material. Rubber simply is higher compliance and so gives more easily. Poly resists more and so there are much greater resistive forces at play (which eventually evacuate the grease and cause the squeaking, I think we agree on this).

Joe, my intended message was to use rubber if you want a comfortable street car or spherical types if you more precise handling and can tolerate increased NVH. I went all spherical in a street car and don't regret it one bit. To give you more context on my setup I have a GM A-body with one inch drop springs that are firmer than stock but not crazy, Bilstein shocks off the shelf, and rubber body bushings.

[BMR Sales]

Kevin, No Biggie, we are close in our thoughts!

T.C.