THSCC Forums

Not strictly true (except the Soylent Green part, that really is people), it's a thermoplastic elastomer, so a plastic with rubber-like qualities. A lot of people like to replace their rubber bushings with it, which I consider a bad idea, because it can permanently deform under stress. In normal driving it might take many years, but at the track it can happen faster. I like to use solid metal bushings, spherical bearings, or Delrin (very hard plastic that will not deform or even deflect), but when I put some new shocks on the Duff car a couple of years ago I put a set of Energy Suspension polyurethane bushings on them, mostly because I'm less critical of shock bushings than control arm bushings. Here's what they looked like when I took them off today:




I've seen pictures of this from others, mostly from cars on race rubber, but this is off the Duff Beer car, which has only ever seen street tires. It may have been driven relatively aggressively a couple of times in the past 2 years , but rubber held up better.

_________________
"Every ship is a minesweeper, once."

*cough*SEBRING*cough*

Not surprising, I would see pretty frequently posts on the Camaro5 forum about my car pulls when braking but the brakes aren't the cause. Or their car pulls to one side under hard throttle, etc. Most often the cause was they put poly bushings in the suspension and they had deformed similar to that.

Sure, they stiffen it up for awhile, but then when they go bad it causes weird things to happen.

_________________
2017 Autocross Chief of Tech

2000 E Street Miata
2015 Focus SE EcoBoost 6 speed
2015 Fiesta ST (Wife's ride)
2012 Yamaha FZ1 sorta crotch rocket? All I know is 150HP and 487 lbs is fun!

Thanks for sharing, Roger. I had a similar experience with my Mazda. I've replaced all the frame-to-body rubber bushings (8 of them) with solid aluminum.




I did poly bushings in all the front control arms (10 bushings) and after 4 HPDEs a couple of them were deformed and loose. I found the ones that were molded/bonded to a shell and pressed into the control arm have held up very well.

Like these (top-rubber, bottom-poly):


The ones that slip into an opening (no outer shell) and just have a bolt sleeve (unbonded) were junk.

Like these (poly-right, rubber-left):


I've switched back to rubber in these applications.

_________________
09 Bullitt - DD
11 Fusion - Wife's DD
03 Mazda6 - Track car
00 PSD Excursion - Tow rig
67 Firebird - Don't you still own your 1st car?
61 F100 - Dad's truck
90 Moto Guzzi Calif III - Tourer
00 Cagiva - Adventure bike
00 DRZ400 - Woods bike

I am switching my car to all delrin except for the eccentrics where it will be a poly bushing with a teflon impregnated bronze sleeve riding on an allow steel center. I figure I will be replacing those every few years but they won't need the constant greasing maintenance of an off the shelf poly setup. These are similar sleeves to what will go in my car:

How often did you regrease the poly bushings? The ones in my Miata don't look anywhere near that bad. Likely close to 100 track hours on them by now.

I greased them when I installed them.

I think Cash has it right, because the ones that are bonded to a metal shell, like my front shock mounts, seem to be holding up better, while the rears, which just slip in the hole in the control arm, are toast.

_________________
"Every ship is a minesweeper, once."

I think all of the ones on the Miata are the split design with the metal sleeve insert.

Extremely interesting, thanks for sharing.

If they deformed like that I'd wager they were used in a suspension part that requires movement on more than one axis. The binding must have been great for handling before the deformation. That's the main problem with any urethane bushings.

Along those lines the first thing that comes to mind is some Honda rear suspension setup that moves about multiple axis. But the problem still happens even when it is about a single axis. Early Porsche 911 (and 914) front suspension uses a macpherson strut setup. On the lower arm there are two mounting points that really only need to rotate about one axis, but you will see that type of deformation in poly bushings due to cornering loads. The same somewhat also happens with the rear suspension (trailing arm).

Common solutions for the 911/914 are hard plastic (Delrin) which has it's own issues or Poly/bronze combo that have a predominantly bronze construction with some poly. And of course there are solid metal solutions for race/track application.

Richard

_________________
Richard Casto
1972 Porsche 914
2013 Honda Fit Sport
2015 Honda Fit EX
http://motorsport.zyyz.com
Money can't buy happiness, but somehow it's more comfortable to cry in a Porsche than a Kia.

They have a metal sleeve, but they aren't bonded. I'm in the middle of replacing the springs/shocks on my Miata. I'll post some pictures if they look trashed as well.

You mentioned this is a shock bushing, I wonder if they are just really poor in applications that take the vehicle weight.

That may be true too. The Civic has coilover springs, so they are supporting the weight of the car, but I never really had this kind of problem with rubber bushings. Also, the front shock bushings, which are thicker and bonded to a metal sleeve, do not have this problem. It may just be that the 2-piece design is not good for this application.

The lower control arm connects to a trailing arm, so there is motion on more than one axis, but the motion on the second axis would be very minor. For the most part, it operates like an unequal-length upper-lower control arm design, which it kind of is.

_________________
"Every ship is a minesweeper, once."

To expand on that, when I used rubber bushings, the ones that got trashed earliest were the front lower control arm bushings, which makes sense as that's where I put most of the stress on the suspension. I can get bronze shock bushings; I may have to try that.

_________________
"Every ship is a minesweeper, once."

Cash, did you buy those metal subframe bushings off the shelf, or have them made custom? I'm looking to have similar (but not the same) work done. Could you pm me, or maybe chime in in my sway bar thread, and let me know who made them?

I'm trying to solve a similar problem. The end link design on the Focus ST rear sway bar is silly. I think it works okay with a stock bar, but with something stiffer, and especially something adjustable, it's hokey.

_________________
Karl S.
2014 Baby, 2014 House, 2013 Ford Focus ST, 2013 BMW 328i, 1994 Mercedes E320
(Insert passive aggressive signature line here)