How do the suspension bushings work???

[Mike Arteaga]

I stumped! I have pulled the rear spindles on my 67" L79 to rebuild the parking brakes and put new bearings in and it looks like I will be taking the trailing arms off since they need attention. I expected the strut arm and the trailing arms for that matter (when one end was disconnected) to hang down!? I assumed that the bushings in the suspension components were free to spin on the their mounting bolts! They don't!! They are pinched tight and all the rotational movement comes from the rubber bushings that seem to be fixed to the steel sleeves that go through them! Even the trailing arms are pinched so that they didn't drop down to rest on the frame but remained straight out after the shocks and rear spring was disconnected form them! They were held there by the rubber bushings that were obviously pinched and stuck to the trailing arm mounting bolt and the trailing arm itself?? Is this the way it should be??? So that all movement in the rear suspension is from rubber being stretched!???
I'd like to understand how this is supposed to work before I put it back together!! Thanks !!! Mike Arteaga #34566

[Wayne W.]

Re: How do the suspension bushings work???

Thats the way it is.

[Duke W.]

Re: How do the suspension bushings work???

It's probably a common misconception that suspension bushings involve some kind of sliding action between surfaces. They don't. All the movement is strain - i.e. deformation in the rubber - like a rubber eraser.

If there was sliding action, there would be wear and bushing life would be much shorter. Bushing rubber is very tough, but hardness varies. For example, on many cars with A-arm or strut suspensions, the lower A-arm rear bushing is softer than the front to allow some aft compliance of the ball joint, which softens road shocks like potholes. Bushings are also "tuned" to not transmit characteristic road input frequencies so the ride is quieter and less harsh.

Because bushing rotation is taken by strain (deformation) of the rubber, it's important that they not be preloaded. This is why the AIM and service manuals instruct you to only torque the bushing bolts to spec when the car is at normal ride height.

Duke

[Dan Tewell]

Re: How do the suspension bushings work???

Mike, If you loosen the pivot bolt/nut and the arm still doesn't hang down, then I think you have a problem with the bolt seizing to the inner sleave of the bushing. This is not as it should be. It makes it a bear to align! I personally believe that the arm should pivot on this bolt. If you can get it apart, just put some never-seize on the bolt and reassemble.
Dan

[Duke W.]

Re: How do the suspension bushings work???

By design, there is no relative movement between the bolt and the bushing innner sleeve. All the motion manifests as torsional strain in the rubber.

Duke

[John M.]

Re: How do the suspension bushings work???

Duke is exactly right. The only exception to this would be a car which has had ureathane bushings installed, as these bushings are designed for the metal sleeve to rotate in the ureathane bushing. This is why this type of bushing used to squeek so bad before they revised the formulation of the ureathane to include a lubricant.

Regards, John McGraw

[Duke W.]

Re: How do the suspension bushings work???

Another exception might be solid axle Corvettes. I recall from my youth working in a gas station in the early to mid sixtes that older cars at the time - early fifties - had zerk fittings at the control arm pivots, so they might have had some kind of sliding contact bushings.

The new '55 Chevrolet supension with rubber suspension bushings and ball joints for the steering knuckle, instead of kingpins was the new state-of-the-art design, which is still used on modern cars, but Corvettes didn't get this front suspension until 1963.

Duke

[John H.]

Re: How do the suspension bushings work???

Yup, C1 bushings are sliding metal-to-metal, requiring copious quantities of chassis grease at regular intervals; C2 and later bushings have the inner sleeve O.D. bonded to the rubber, which is also bonded to the I.D. of the outer sleeve. The ends of the inner sleeve are serrated so that when the through-bolt is torqued, the inner sleeve is captured and held stationary by the bracket walls on the frame (or by the stepped diameters and retainers on the front control arm cross-shaft); all motion is absorbed by the rubber - the inner and outer sleeves are stationary in all rubber bushing applications (including trailing arm and camber strut bushings).

[Dan Tewell]

Re: How do the suspension bushings work???

Duke, John, I value your knowledge, but as I was telling Mike, there is a good chance that the bolt is rusted to the inner sleave. I've seen my fair share of these come through my shop. If GM would have put ten cents worth of never seize on these bolts, this would never happen. I always add never seize and replace with urethane bushings. Not origional, just better!
Dan