bushings

[Michael Oritt]

I know we have kicked around the subject of bushing material before but can we do it again?

Of the various materials (rubber, poly and nylon) what are preferences and recommendations for "moving" and "non-moving" joints, and what for road and race and why?

 

[zblu]

Iuse a bit of "silicone" grease to put them in with, not normal silicone grease, we use it in the dive gear, prefer rubber if you can get the quality from yesteryear, just finished trashing an austin, and the rubber bumper to body closures are still in good nick and flexible after 50 years+!

 

[Dave Russell]

There are so many diverse opinions on the subject that I hate to get into it.

If you are talking about suspension bushings such as the inner lower A arm pivots on a Healey, I feel that the conventional steel sleeve bonded rubber type is the best. The metal parts of the bushing are firmly clamped mechanically & rely on twist (torsion) in the rubber for movement. They obviously don't require supplemental lubrication.

Poly & nylon bushings are not bonded & rely on movement between the bushing & the adjacent metal. They usually require lubrication which is not provided for. These bushings are often available in several hardness grades.

For bushings that do not rotate, either will work. Rubber gives the softest action. Stiffer bushings also transmit more force to the mounts & put more stress on the attaching parts.

For "race" bushings, where things are frequently replaced, disassembled for regular maintenance, ect., hard bushings are favored for the last little bit of control precision,-- maintenance, mount stress, noise, harsh ride, are secondary.

Since so much of it is personal preference, I think you will just have to go with what you think is best. It can always be changed back if you don't like the result.
D

 

[MarkA]

I recently installed a set of poly bushings up front of my BJ8. A lot more (than I expected) road "noise" gets transmitted through the car. My biggest complaint started 6 months after installation. The assembly lube has worn out or dried up and now I get bushing creaking when there is a lot of movement in the arms. I plan on going back to stock bushings when I have some free time.

Mark

 

[BUNDYRUM]

I would have to agree wholeheartedly here with Dave Russell once again.

My theory is that as far as the suspension mounts go they were designed for rubber/metal bushings (the original type) and not for solid bushings.

If however you want to go and completely redesign the suspension mounts and the way they mount to the chassis then I'd say go for the hard "poly" bushings.

bundyrum.

 

[GregW]

I’ve heard the issue is the horizontal planes of the upper and lower control arms are different. The lower arm slopes down 2° towards the front if memory serves me.

 

[Dave Russell]

I’ve heard the issue is the horizontal planes of the upper and lower control arms are different. The lower arm slopes down 2° towards the front if memory serves me.

Hi Greg,
I think it's that the lower control arm mounts are square to the frame rather than square to the control arm pivots which are slightly angled. Ie - Twisted two degrees out of alignment. The castor is produced by mounting the front of the lower control arm higher than the back is mounted. This effectively moves the bottom of the king pin forward of it's top which creates the castor. (The projected king pin axis hits the ground ahead of the tire to ground contact point.)

There is an interesting discussion on the subject here:
https://www.netbug.net/blogmichael/?p=103

If you read down through the comments you can see where John Kilmartin disagrees with Jim Hockhert & I.

I think John is referring to the upper & lower arms being out of alignment.

The bind problem is just that the lower mounts are cocked with regard to their pivot axis. The lower mount vertical ears should be tilted two degrees back in the vertical plane to remove the bind from the bushings.
D