Has anyone had experience installing or currently run polyurethane bushings on there c4? My original rubber bushings have never been replaced so its probably time and im wondering if its worth the extra money to get the polyurethane ones. heres the kit im looking at https://www.carid.com/energy-suspens....html#features

 

Do yourself a favor and do a search on Super Pro here on the forum. Super Pro bushings are better than plain poly.

 

I don't know what you mean by "extra money." There are no stock rubber bushings available anymore, so regular poly bushings are the cheapest thing you can use. They are okay up front, but they should not be used in the rear because the links all have to swing in multiple arcs and the hard poly bushings will cause bind. Super Pro are a much better option because they allow more off-axis flex without a lot of bind.

 

For the average driver, I have to question this being an issue. I haven't noticed any handling "problems" after changing mine to the black poly (impregnated graphite) bushings -- 5 yrs ago. And...HOLY COW those SuperPro's look expensive as all get-out. I didn't even see Chevy listed on their website but most "kits" were $500-$1k!!!

Also, I wouldn't think there'd be THAT much "out-of-plane" articulation (after see how it all "works" via bushing change). Plus, the graphite-impregnated bushings should allow some "slide" if not enough flex???

 

I would argue that it's actually worse for the average driver. The bind I'm talking about creates a rising-rate rear suspension, and that creates snap oversteer. For a track or autocross car, that makes it difficult to push hard because the handling is not linear and predictable, so you lose time. For the average driver trundling around the street, he'll never understand how it feels or how to deal with it until he has an emergency avoidance situation and the rear end comes out suddenly. He loses a car and maybe gets hurt. Add to that the possibility of tearing apart frame brackets where the links mount, or worse yet damaging the aluminum knuckle. Fox Mustangs were/are infamous for ripping "torque boxes" off their frames after people misguidedly installed poly bushings in their rear control arms. Bad idea.

If you want further evidence, not that Global West and Van Steel make Delrin bushings for C4 front links, but they won't make them for the rear. Guess why? Delrin is even harder than hard poly bushings, and they know how badly it would bind.

There is no significant "slide" along the bushing axis in a properly installed poly bushing: the bolt-nut should be torqued down so the two frame tabs capture the inside sleeve and keep it from turning, and they pretty closely capture the poly also (just not quite). If they could like you say, then the suspension geometry would change.

As for how much movement off axis there is, if one trailing arm is 12" and it sits parallel to ground with the car at resting ride height, and the camber rod is perfectly on its bushing axis in that condition; then compressing the suspension 3" will pull the end of the camber rod 0.4" off axis. If the camber rod is 24", then both trailing arms will also be getting pulled 0.2" off their bushing axis. That's no big deal with rubber bushings, but it is with hard poly. Each link will require significant force to pull it that far off axis (there are two bushings exerting force for each link), and then you have to add up those forces from six links. So we're adding up the force of 12 poly bushings being pulled that far off axis. It's a rising-rate force that is added to the roll resistance provided by the spring and sway bar. And the softer the springs and swaybars (again, going back to the "average" driver in a softer car, even with C4s), the bigger an effect it will have on the handling.

 

Right now they are out of stock, a person would need to call and find out when more are heading into the country.

With that said, a complete C4 Corvette set is $325.00 to $350.00

https://www.corvettepartscenter.com/collections/c4/products/late-1988-1996-corvette-suspension-bushing-kit

https://www.corvettepartscenter.com/collections/c4/products/1984-mid-1988-corvette-suspension-bushing-kit

 

Pretty sure I get what you are saying...at least in general. But, I'm not convinced you identified an issue Poly bushing manufacturers would never think of? If the Delrin guys thought "Hey, we can't make a SUPER RIDGED part for the rear control arms, why wouldn't "poly guys" work on a poly "formulation" with some flex? You know...like tire guys design formulations for temp, use, and comfort? Did you run a study to show poly bushings are problematic? I can see before/after on track day leading to this conclusion but there are (at least) 3 makers of poly bushings....or there were 5yrs ago.

It's also not clear how problematic worn rubber might be -- in comparison to new poly? I'm not challenging your premise about firmer suspension bushing -- just that the problem has been "measured"...and for all options.

What are these SuperPro bushings made of? Sounded like a poly (blend?) to me....when I read a blurb off their website.

EDIT: Also, it's been too long since my reading on rear end suspension...Don't the use of 2 trailing arms help to keep up/down articulation more "linear"?


NOTE: I assume you're saying the rear-end "loads up" under turning forces and springs back HARDER than with rubber -- kind of "shooting" the rear around a turn. Since poly is firmer than rubber....or at least presumably is. The result is "snap oversteer".

 

Economics. The current formulation works just fine for the majority of cars that they are targeted at. Out of all the old muscle cars and such, the only really popular car with independent rear suspension is the Corvette. It is the articulation that makes the heim joint solutions work so well.

Plus it is the rest of the old car guys that spend money on their machines, do you notice how many ratty C4 Corvettes AND later model C3's for that matter are on the road ? Around NE Ohio there are lots of beaters driving around.

Also handling. The solid rear axle cars get their suspensions really tightened up with polyurethane.

 

I wondered about the trailing arms and heim joints. If I understood Matt, that wouldn't change the issue for the lower rear control arms, right? Poly bushings vs heim joings on the trailing arms may not allow true up/down of the lower control arm?

I did a quick search on poly vs rubber bushings oversteer and didn't find much. WAY more websites tout the use of poly saying mild increases in vibration/feel were offset by improved geometry since components stay more in their "plane". Like this one...

https://dsportmag.com/the-tech/quick...t-to-the-test/

Looks like similar control arms on the Miata...though you can't see in front of the suspension (trailing arms or ???)

If I understand correctly the main point of concern is where the control arms attach to the rear diff carrier?



EDIT: This sight provides some counterpoint (to the one I linked 3 lines above...
https://www.iwsti.com/threads/bushin...ethane.206293/

 

They don't formulate their own polyurethane, I'm almost sure of that. They are just buying "bar stock" and milling it down, or buying off-the-shelf ingredients and pouring their own molds. SuperPro apparently is using something fairly unique, but more likely they didn't develop it but rather found it and made an exclusive deal with the company that makes it. They would have to be molding that instead of milling it, I'm sure.

Anyway, the regular poly bushing makers are vying for being able to advertise the least flex possible. Just look at their ad copy touting why their bushings are so much better than stock rubber. That's why they don't look for poly formulations with more flex. They've spent many decades convincing consumers that bushing flex is universally bad. I've got news for you: they don't care how your car handles. They care about convincing people who don't understand suspension dynamics that stock rubber bushings are terrible and they will have an F1 car if they just put hard bushings everywhere. And since 99% of their customers never really drive their cars hard, they don't know the difference. You see the same thing with suspension companies that encourage car owners to replace their "flimsy" stamped U-channel control arms with boxed or tubular ones, and the exact same thing happens: bind, because the torsional flexure of the stock parts was designed in on purpose to prevent bind. The vast majority of aftermarket companies have no idea what they're talking about and/or have no intention of making cars handle betters: they are marketers of crap, pure and simple. The Banski and After Dark Speed types of companies are few and far between.

I drove my 96 with rubber and then poly, way before I owned it. It wasn't good. There is copious engineering research to show how a rising-rate bind condition affects a suspension. No need for me to repeat that research.

They aren't very different in durometer hardness, though...except for SuperPro.

No, I'm not talking about linear movement - I'm talking about linear wheel rates. The amount it takes to compress the wheel a certain amount. Like a linear spring with a rate of 500lb/in requires 500lb to compress it another inch no matter how compressed it already is. The bind I'm talking about rises in rate quite rapidly, meaning you have a rear wheel of some amount at rest and a significantly higher roll rate after the car has already rolled some amount...meaning your handling balance can change from mild understeer to oversteer in the time it takes the car to lean in a turn. That's snap oversteer.

No. You're going to read some basic suspension theory to understand how relative wheel rates between the front and rear affect handling balance. Suffice to say the stiffer the rear suspension (roll rate) relative to the front, the more grip the front has and the less grip the rear has. With a binding rear suspension you are making the rear gain relative stiffness very quickly as the car leans into a turn, which is the worst possible time to do that.


Heim joints allow rotation in any axis around a single point. They have no bind in any plane as long as you don't try to exceed their limits of travel. They are the best bushing replacement for the rear of a C4 in terms of performance, but are definitely overkill for street driving.

Quote:

I did a quick search on poly vs rubber bushings oversteer and didn't find much. WAY more websites tout the use of poly saying mild increases in vibration/feel were offset by improved geometry since components stay more in their "plane". Like this one...

Most websites have no idea what they're talking about. This one talks about poly bushings reducing the roll angles of a Miata. That tells you they are stupid. You should never pay any attention to their tech articles, because they don't understand this stuff. Also, the Miata's rear suspension may not require its links to move in multiple axes. I'd have to study it more. I know its front doesn't, and neither does the C4's. Poly bushings are fine up there. The C5 rear suspension has upper and lower A-arms and also is probably fine with poly bushings.

Quote:

If I understand correctly the main point of concern is where the control arms attach to the rear diff carrier?

On a C4, the point of concern is both ends of both camber rods and all four trailing arms: 12 bushings, as I wrote before.

Quote:

Originally Posted by drcook

Also handling. The solid rear axle cars get their suspensions really tightened up with polyurethane.

Solid axle suspensions will bind with poly bushings also. It can be even worse, because not only do the control arms often have to move in multiple axes but when the car rolls the arms have to allow torsional movement because the axle doesn't roll along with the sprung mass. That's why they all came with stamped U-channel control arms that were rigid in tension and compression but flimsy in torsion. And so many "hot rodders" screw this all up buying stupid boxed or tubular arms that are stiff in torsion and come equipped with poly bushings. Super snappy, and then they also start breaking control arm mounts.

 

well matthewmiller you seem super well versed in this stuff so im gonna take your word on it lol, im planning on tracking and maybe some light drifting for my vette so snap oversteer doesnt sound too fun. ill look into the superpro bushings and see if i can find a set of those. thanks everyone for the info i appreciate it hella

 

I was speaking more about sticking the bushings into the spring eyes, or in the old school coil spring cars, into the arms that only move in 1 linear plane and the front control arms which also only move in 1 linear plane. The ones that I have worked on had a bar that went in between the ears on the front A-arms and the bushings were pressed in over the ends. Then the bolt holes to attach to the frame were in the middle.

The control arms really only move up and down on the front. I suppose that there would could be some out of plane movement on rear control arms (coil spring cars) but when the old black rubber got hard, there was no movement other than around the bolt.

When I torched the bushings out of the front a-arms of the '65 I did the bushings were hard hard hard.

Then you look at these. The articulation is coming from multiple pivot points that allow movement. Any radial deflection in the bushings is secondary and can cause a lot of stacked up slop.

https://www.drivingline.com/articles...tion-got-flex/

 

Yep, poly bushings in the spring eyes of a rear suspension are just fine.

There's no solid axle setup where the control arms only move in one plane, though. If the arms are all parallel they will stay in plane when both rear wheels move equally (squat or lift), but when the car rolls then the control arms have to be pulled off parallel (the axle ends move closer to the centerline of the car) and they also have to twist.

Yes, in the front control arms poly is fine.

Yeah, those guys take it to an extreme. I don't know enough about their suspensions to say how their bushings look, but you'd think that would be the ideal case for heim joints.

 

Here are some really good pictures of the different types

https://monroe.com.au/trade-corner/t...ear-suspension

The entire car "works" on all four corners, limiting how much deflection is at the bushings.

I agree, when new, that rubber bushings absorb and allow suspension pieces to move before the rest of the car starts moving and relieving radial twist through other suspension pieces moving. The entire car "works". If you have a lift under the right rear tire, the left front starts to squat, relieving radial twist in the suspension components/bushings themselves replacing it with mechanical motion on all four corners.

I found out about rubber bushings 43 years ago when I started into the Corvette world. When I worked in a defense shop, the military used lots of Teflon components. I saved bar ends. I machined bushings for the shocks and sway bars on the '65 I had. The rest of the suspension was new, I stripped it to the frame and rebuilt the suspension back. With the addition of the Teflon the suspension was quick and tight. The guy I sold the car to almost wrecked it going home it was so quick. He was an experienced Corvette guy, but experienced with a suspension that just didn't react.

The Del-alum (and other solid) bushings, while imparting a harsh ride don't have the tolerance stack up from rubber squishing before the rest of the car moves. I would surmise that this is what cracks polyurethane. I have had poly shock bushings crack on my trucks through the years. It starts compressing before the shock internals start to move. Over and over and over until it cracks.

Black rubber compresses before the rest of the suspension moves, over and over and over, until as it ages and gets harder, and then starts wallowing out, or becoming so bound up, the suspension just doesn't work. The '65 was a combination. Some of the front control arm bushings were wallowed out, some were just twisting the sleeve inside the rubber.

This is why I like the pin-top shock bushings that I got from Banski so much. It is the shock internals moving, not the bushing compressing and then the shock internals. I will say though, there is some radial movement at the top of the shock. This is relieved by the top of the bushing being machined spherically, with the "washer" on top having a corresponding internal cut, that forms a ball and socket.

 

The c4 bushings were service by replacing the component they were made to or other words suspension bushings weren't available as a service part. As previously stated front suspension moves linear. There is more options from Poly to roller bearings, with the rear every part of the suspension is moving up, down.,in and out. The stiffer the bushing material the more binding that occurs. Now, these are old cars was in many cases the bushings are cracked and failing. Poly is far better than the arm riding on the bolts. NOS rear links do show up from time to time. I had worn-out bushings the were falling apart. I installed pro thane kit. I noticed the binding in during reassembly,. I haven't been able to commit to spherical rod ends on a primarily street driven car. Although If I were competing I would. Banaski sell boots for their rod ends to reduce wear from debris.

 

I could honestly tell no difference between Banski rod end links vs stock rubber in terms of ride quality. Road bumps really aren't absorbed by the bushings/joints in either the trailing arms or the camber rods, so there is minimal effect on ride quality. I do agree that the rubber boots would be a good idea for those who are street driving cars with rod end links. However, typical rod ends aren't very expensive to replace, so it's not a big deal either way. I daily-drove my C4 for about two years with the Banski parts and no boots.

 

When I priced them from Rod End Supply (down the road from my house), it was about the same price as buying complete new rods.

 

At some point I needed to replace a couple ends on the Banski links I had. They were off-the-shelf Aurora teflon-lined rod ends and I believe they were maybe $15-20 each.

 

I might be remembering this: $[8 new rods ends] + $[4 used trailing arms] = $[all new trailing arms from Banski]

Of course, that's when Banski still carried them. Maybe the ends WERE $20-25 each at Rod End Supply? I remember they had two types....One might have come with zerts?

If they were [some-how] sealed, I probably would have gone for it.

I wouldn't be surprised if all new ends for trailing arms > $200. At least SOME ONE still sells trailing arms and control arms with heim joints. If I wasn't retired, I'd probably "upgrade"...even w/o being sealed. Now-a-days, I try to keep all four tires ON THE GROUND! LOL

I just didn't know poly was "that bad". I had the ***-end kick-out one time. Almost clipped another car. ALMOST - BUT NOT QUITE! That's the only time since 1999. And, I still had the OEM rubber. At least it wasn't as bad as a co-worker I let drive the car when "new". He got up to an intersection, floored it -- while turning -- and did a 180. Immediately got out of the car and walked back to work. I had to run and get it! LOL Some people can't drive worth a crap.

 

Vansteel, amongst others are still offering componentry like Banski's. Banski is out of most components, is in the process of:

Ridetech has some components now, HOWEVER, nothing is inexpensive. Everything is now mucho dinero. Super Pro is the best remaining option for most people in my opinion.

https://www.ridetech.com/new-corvett...-even-tighter/

https://www.ridetech.com/product/198...trailing-arms/

https://www.ridetech.com/product/198...ower_11567295/

https://www.corvettecentral.com/c4-8...-arm/?count=45

https://www.vansteel.com/index.cfm?f...&subgroup=1906

Rubber boots for rod ends are available on Amazon (other places also) really inexpensively. The installation tool for the rubber boots is inexpensive and also available.