Center link...now what?

raygreenwood · Post by **raygreenwood** » Fri Jul 25, 2008 11:50 am

No Problem. And yes...it was the reboundrate...or elasticity of the urethane that got you. Thats the problem with urethane.
Rebound (bounce or elasticity) are not linear with durometer. There are tthousands of formulations.
I think the new mod with the ball will be better all around. It is simply a ketch on a micro-soft word document but you will be able to see the gist. Ray

ubercrap · Post by **ubercrap** » Fri Jul 25, 2008 12:59 pm

raygreenwood wrote:not linear with durometer. There are tthousands of formulations.

Crap, that's what I thought. I should have known, though- the stuff I had was so elastic, it was tough to even cut, drill, or shave it with a dremel- just wanted to deform. It was "stiff" in a way- difficult to compress, but very elastic in that it wanted to stretch easily. I could see the ball idea being better than the plate collar design- it would lessen the pinching that caused the donut to pop over the collar I bet.

raygreenwood · Post by **raygreenwood** » Fri Jul 25, 2008 1:44 pm

Yes.....and if we also have much better control arm bushings that greatly lessen the need to have a really flexible donut there....it just becomes more of a rotational issue.

In fact...The only real compression that happens to the donut...is from that dang disc welded to the bar.
The only rear the reardonut exists is to damp rebound from when the front donut gets compressed slightly...or pinched from rotation...and causing flexing.

Just like going to Delrin for the control arm bushings....
The conventional wisdom has always been that you had to have a rubber based bushing to keep from transmitting vibration.

Audi found that not to be true a few years back when they went to Delrin on A-4 control arm bushings. As long as you are not requiring the bushing to be a point of flex or shock absorption....there is not need for an elastomer....just a vibration damping material that is still rigid.

I think the same issue holds true for our control ram bushings....and even more so with teh radius arm donuts.

Picture this...if there is no real for and aft movement......AND.....you get rid of that flange that compresses the donut during rotation of the radius arm....you could easily make that forward donut into something rather rigid but low friction to aid rotation.

A rigid forward bushing would also locate better in the "eye"...to keep up and down motion at bay....and you could for the sake of keeping things soft and keeping tension on the whole mess...have only a rubber or urethane donut in the rear donut position.........or better yet...just a fat freakin spring around the end of the shaft between the rear washer and the back side of the ear. Ray

wshawn · Post by **wshawn** » Fri Jul 25, 2008 1:44 pm

Rather a long link but there is a centre link on e-bay now, I'm assuming these are for left hand only and as mine has the steering on the 'right' side of the car of no use to me

http://cgi.ebay.com/ebaymotors/NOS-VW-T ... 0241195657

ubercrap · Post by **ubercrap** » Thu Jul 31, 2008 10:59 am

Ray- I have been thinking- is there a real need for the donuts to be perfectly cylindrical? Could they have more of an oval profile/cross-section? In the case of the material I have, maybe this could keep them from being pinched to the point of popping over the collar?

wshawn · Post by **wshawn** » Thu Jul 31, 2008 11:51 am

An interesting idea, I have decided to go with Rays idea of cutting of the flanges/retainers and replacing them with half-balls but your idea sounds like an easier version of that? Making the bush into a curved surface for the pivot?

raygreenwood · Post by **raygreenwood** » Thu Jul 31, 2008 12:10 pm

I have tried that a long time ago. It helps....but its just not enough. The only thing I have not tried...is a radiused oval donut like you are suggesting....and a reduced diameter on the flange.

the other issue is that pinching the donuts also is what responsible for most of the wear and damage to the center ring gromment undernearth.

Its worth it to remember that the only reason the large flange and donut on the radius are important is because the original control arm bushings had no way to control backlash of the radius arm.
Whether through tire force or bumping small obstacles at speed....the original control arm bushing softness and lack of a flange...continually smacked the radius arm flange backward against the donuts. A lot of that will be gone with new control arm bushings.

The problem with the flange pinching the donut is a defect of design. It only happens because the end of the radius arm is bent at angle out of mounting necessity.....it also only happens on maximum strut compression and extension.

The real problem with having the pinching action of the flange and donut...is that every time it happens...it pushes the donut sideway...elongating the hole in the center and mislocating the donuts seat in the eye socket. It allows the load of the radius arm to fall completely on the plastic centering ring...which beats it out of round.

Its just a bad design. Having a radiused donut mean that when it goes to full pinch its easier to shove out of the set. Its an improvement for sure...just not a complete answer.
I think its worth trying to reduce flange diameter by say....1/2" and using a crowned donut. Let us know how it works. It certainly will not break anything.

Of course going to a half ball....AND flanged control arm bushings alleviates the issue totally. Ray