Board logo

Polybush point of rotation?
cloudy - 21/6/06 at 10:35 AM

On a suspension bushing, is the actual part that rotates the metal sleeve on the mounting bolt, or the sleeve on the poly bushing?

Thanks,

James

rayward - 21/6/06 at 10:57 AM

HI,

the metal sleeve (crush tube)stays fixed, the bush rotates around it.

Ray

Avoneer - 21/6/06 at 11:12 AM

Can 'o worms...

Pat...

cloudy - 21/6/06 at 11:28 AM

well the sleeves in mine are stupidly tight, any suggestions for loosening them up?

James

DaveFJ - 21/6/06 at 11:40 AM

Can anyone say "Arrrrrrrrrrrggggghhhhhhhhh......."

cloudy - 21/6/06 at 11:57 AM

sorry, I take it this is a much discussed and sore topic!

James

NS Dev - 21/6/06 at 12:00 PM

dunno why? The bolt pinches the bracket onto the crush tube and the bush and wishbone etc rotate on it, simple as that! If they are tight, drive it for a bit before worrying, they will usually loosen up pretty fast.

David Jenkins - 21/6/06 at 12:04 PM

Originally the discussion was regarding rubber bushes, and whether the steel inner tube should rotate on the bolt, or if it should be clamped tight so that the rubber does all the work.

There was no agreement, the discussion split into 2 camps, and in the end very few people cared anyway!



rgds,
David

cloudy - 21/6/06 at 12:09 PM

Thanks guys, the worry was more as to whether I needed standard bolts or whether I need an unthreaded portion of shaft for the crush tube to 'run' on

James

MikeRJ - 21/6/06 at 12:32 PM

IIRC the camps were split into almost all people beliving that a mild steel/mild steel bearing interface was a really bad idea and that the crush tube was not machined to the required tolerances anyway, and one or two people thinking it was a good idea.

With a polybush, the bush is the bearing material and should rotate around the crush tube which should be tightly clamped in the suspension bracket.

My GTS bushes are very tight, because the tube into which they are pressed is a little too small, but I think they will loosen up quick enough.

JoelP - 21/6/06 at 05:18 PM

the actual fall out in the original thread revolved around the length of the crush tube. Everyone agreed it should be clamped tight, but it wasnt agreed if it should be slightly longer (to leave the bush clearance to move freely, but some claimed it would be sloppy loose), or the same length, or slightly shorter, leaving the bush fractionally compressed but still hopefully free to move. I guess the shore rating affects this, myself id say make them the same length, but in reality i'd use a spherical bearing/rose joint.

MikeRJ - 21/6/06 at 07:44 PM

quote:
Originally posted by JoelP
the actual fall out in the original thread revolved around the length of the crush tube.


That was a different thread to the one I'm thinking of then, which was definately about the crush tubes revolving on the bolts. I searched for the original a while back but it appears to have been deleted.

JoelP - 21/6/06 at 08:19 PM

many old threads and posts have been deleted! It is hard to imagine why the crush tube would rotate on the bolt, and surely it wouldnt then be called a crush tube!

907 - 21/6/06 at 09:08 PM

quote:
Originally posted by cloudy
well the sleeves in mine are stupidly tight, any suggestions for loosening them up?

James



I had the same problem James.

My crush tubes were 9/16" o/d so after inserting them into the wish bone I ran
a 9/16" drill through them to ream them out.

When mounted on the chassis now they are tight enough to hold themselves up
but can be moved up and down with one finger, well, maybe two,
that is without the upright on.

I think my problem arose because of shrinkage of the w/bone eye when I welded them.
Serves me right for using stainless.


HTH

Paul G

NS Dev - 21/6/06 at 10:54 PM

quote:
Originally posted by David Jenkins
Originally the discussion was regarding rubber bushes, and whether the steel inner tube should rotate on the bolt, or if it should be clamped tight so that the rubber does all the work.

There was no agreement, the discussion split into 2 camps, and in the end very few people cared anyway!



rgds,
David


sorry to be blunt (and not to you I hasten to add David!) but one of the camps was evidently full of complete prats then!!!

Why use a bushing material if you are going to pivot the suspension on a metal to metal joint on a bolt!!!?


Duh, doesn't take much thought really to realise that is going to wear the bolt out very quickly!!!!!!!!!

Crikey.............and they're building cars, thank god for SVA!

C10CoryM - 22/6/06 at 03:46 AM

Not going to get involved in the "can 'o worms" but Ill probably get yelled at for my next comment anyhow........

Poly bushings suck!

I built up a camaro and used poly bushings in the control arms. I was deflecting the rubber ones badly, and on a daily driver I figured solid bushings were too much.
After a couple weeks of hard driving and a couple weeks of sitting (blew something up, dont remember what went that time) the poly bound up to the point I didn't trust the car on hard bumpy corners. Which when you think of it is damned near every corner.
Did a little research into it and found that poly has some propeties that make it a poor choice for bushings. To start with it is a sticky material. Meaning that unless you grease it on a weekly (daily?) basis it will grab hold of the steel sleeve when loaded hard. Rather than delrin or teflon that will slide even with no lube. Its wear properties are poor for a bushing and it also cold creeps (very slowly oozes out).
If I was getting such severe bind in my heavy sow of a camaro I am suprised that a light weight locost doesn't notice it more. Less load on the bushings to squirt the grease out maybe?

Anyhow, I really recommend against poly bushings unless they at least have a grease nipple. If you need to reduce the road noise go for rubber. If you need something that works well as a bushing use delrin bushings or rod ends. Delrin is easy to machine too if required.

One thing I do like poly for is static mounts (engine/trans). They suck up lots of vibration but do not squish as much as rubber.
Cheers.

leto - 22/6/06 at 05:29 AM

quote:
Originally posted by C10CoryM
Not going to get involved in the "can 'o worms" but Ill probably get yelled at for my next comment anyhow........

Poly bushings suck!
.........


Well, almost

I can't say i disagree with you but just to make things clear. “Poly” isn't a material, it's a wast grope of materials. Even PU is a group of several hundred different materials. The one you used was obviously not suited for it's task, some other material within the same group might have worked better.
The bushings (in the suspension of a locost) have to be somewhat elastic as well as a good bearing. Delrin is a good bearing but not elastic enough to work in a fourlink e.g. Some PU-rubber materials have, with the help of lubrication, both the desired qualitys. As to finding the right one: Good luck!

Cheers!

C10CoryM - 22/6/06 at 02:08 PM

I know what poly means, I'm just too lazy to type polyurethane
The ones I used were from Energy Suspension and were supposed to be black graphite impregnated. One would hope they would use the best available polyurethane in their components but I never confirmed that.

Yes delrin is too hard for a 4link, or any suspension with bind, but it works well in an IFS.
Thanks for adding to my post, I often leave important bits out in my haste.

Cheers.

cloudy - 22/6/06 at 02:14 PM

can. open. worms. everywhere!