Rubber Control Arm Bushing Recommendation?

[Dr G]

Hello,

I am building some new control arms for my vehicle (to add caster).

Since it is mostly street driven and LA roads are getting pretty beat up, I want to use rubber bushings for the lower control arms.

It's sort of a Mustang II style setup, with a 12" long bolt going through both control arm bushings, which are currently small poly units. The bolt is 5/8" diameter.

Question = could anyone recommend a vehicle type (and model year) that employs a good size, rubber, lower control arm bushing, which accepts a 5/8" bolt?

I bought some for '73 and up Chevelle which looked quite promising, but the ID is actually 9/16". Too bad.

I don't care much what type of car they come from.

Thanks in advance for any assistance.

Gustave

[bret]

We have these made for us:
http://www.ridetech.com/store/rubber...ng-insert.html

We use them is several applications of control arms and 4 links. They need about a .050" interference fit to "crush" the rubber for proper operation.

[Dr G]

We have these made for us:
http://www.ridetech.com/store/rubber...ng-insert.html

We use them is several applications of control arms and 4 links. They need about a .050" interference fit to "crush" the rubber for proper operation.

Thank you Bret. That is exactly the type of bushing I am searching for. However, no dimensions are given on the webpage. Are they made to take a 5/8" bolt? I assume so, since you recommended them based on my post, but just thought I'd double check. You have some very usefull fabrication related hardware listed their which I was not aware you offered. Thanks for the tip. Is one of the listed weld on sleeves the correct size for the recommended bushings? That would be even better as I would not have to make them.

Gustave

[Dr G]

Bret - Regarding the weld-on sleeves, I read your site more carefully and saw that p/n90001595 is indeed intended for the p/n 90001942 rubber bushing. Excellent.

Now just need to know if the bushing is 5/8" ID?

Also, I assume the 0.050" "crush" you refer to is in the axial direction. Are these bushings designed to "twist" in operation? That's what I'm used to from my experience with BMW's. It's this twisting action that makes rubber bushings very low friction, and why I don't like poly or Delrin for moving parts.

Gustave

[dontlifttoshift]

Honest question.....How is twisting rubber less friction than a properly designed delrin bushing? Don't get me wrong I like rubber bushing in most applications but I have never heard of using rubber for less friction.

Donny

[Dr G]

Honest question.....How is twisting rubber less friction than a properly designed delrin bushing? Don't get me wrong I like rubber bushing in most applications but I have never heard of using rubber for less friction.

Donny

In a twisting rubber bushing there are no parts sliding against each other, unlike a Delrin bushing. Sure Delrin is a "low friction" material, but when used for bushings, movement of the suspension depends on some steel part sliding within the Delrin.

With a twisting rubber bushing the only friction is within the rubber molecules moving around, which as shown by tires getting hot, is not zero. But not on par with sliding friction.

Now I have not quantitatively measured this. But if you ever get the change to grab an unfettered suspension part which is held by a rubber bushing, and move it up and down, you can feel the lack of friction. A returning spring force sure, but very little dissapative friction.

Gustave

[bret]

Most suspension components move in a very narrow range...maybe seeing a total of 20 degrees of rotational articulation. A properly designed rubber bushing will accommodate that range of rotational movement very well. As the degree of rotation gets toward its limits the rubber offers more resistance, inducing somewhat of a "progressive" spring rate. That is why it is recommended that you set the final torque on suspension components at ride height instead of hanging freely.
Rubber also does a nice job of isolating road noise. Where it sometimes falls short is the precise positioning of the suspension component in the horizontal plane...resisting the turning and braking forces that are induced in spirited driving. Depending on the overall suspension design this problem can range anywhere fron completely insignificant to miserably significant.
Delrin is a really nice material to provide precise positioning of a rotating component with a minimum of induced friction. It's shortfall is that it typically cannot accommodate lateral articulation [misalignment], and it does not absorb as mush road noise. It is also quite expensive [at least in its current machined bushing format].
Bottom line...if you are fabricating a street suspension that will see a couple track days per year...use rubber. If you are chasing serious performance...use Delrin [or Delrin/Kevlar lined heim ends].

[dontlifttoshift]

Doesn't the added "spring rate" of a rubber bushing trying to twist negate the advantage of assumed low friction?

Again, not being a jerk, but this is an entirely new theory to me.

[Dr G]

Doesn't the added "spring rate" of a rubber bushing trying to twist negate the advantage of assumed low friction?

Again, not being a jerk, but this is an entirely new theory to me.

In bump (compression) the spring force of the rubber bushing adds very slightly to the overall spring rate. It is progressive as Bret mentions, so the further the suspension moves from its neutral point, the more the added spring force. But it should still be small relative to the force produced by the actual spring. In droop (extension) the rubber bushing acts against the spring a bit, and in theory you might change your rebound damping to compensate. But the bushing spring force is just too small to worry about.

Over the years I've tried and driven with it all, street auto-x and track. Rubber, poly-urethan, Delrin, and Heim joints (rod ends and spherical bearings). On the street Delrin is very harsh. So are rod ends, but if they are PTFE lined, then at least their low friction makes up for it to some extent. Due to lack of impact resistance over potholes etc, they do tend to get worn out rather fast though.

Gustave

[bret]

"Harshness" is somewhat subjective. Rodney, our development fabricator here, has a 96 Suburban with a full air system and a custom 4 link. We changed from all rubber to all Delrin bushings about 4 months ago to test some upcoming products. He reports no change in the ride quality...it might have even gotten better. I don't have a definate explanation for this...just reporting observed results.
We changed all of our shocks over from Poly to a kevlar lined bearing about 2 years ago. That change eliminated all bushing failures and I feel the ride quality actually improved. Bearings had gotten a previous [deseved] bad reputation for noise because many manufacturers used a cheap chinese bearing that got loose and rattled. The good kevlar lined bearing have shown no such tendencies.
I think all these materials have merits...it's just a matter of which performance criteria is most important.

[Bryce]

"Harshness" is somewhat subjective. Rodney, our development fabricator here, has a 96 Suburban with a full air system and a custom 4 link. We changed from all rubber to all Delrin bushings about 4 months ago to test some upcoming products. He reports no change in the ride quality...it might have even gotten better. I don't have a definate explanation for this...just reporting observed results.
We changed all of our shocks over from Poly to a kevlar lined bearing about 2 years ago. That change eliminated all bushing failures and I feel the ride quality actually improved. Bearings had gotten a previous [deseved] bad reputation for noise because many manufacturers used a cheap chinese bearing that got loose and rattled. The good kevlar lined bearing have shown no such tendencies.
I think all these materials have merits...it's just a matter of which performance criteria is most important.

Agreed.

I have kevlar lined races on all my chromoly rodends on my car It dont really notice much harshness.