well, i installed the energy front and rear control arm bushings, and the sway bar end link bushings. I am extremely happy with the ride and had no issues. I just recommend lubing the ever living crap out of them when installing. Make sure to clean the old rubber that is left behind in some of the holes when removing the old rubber. The aren't noisy nor do they squeak.

 

I know it's not the popular opinion, and I'm in no way an expert but I installed the Energy Suspension poly bushings all they way around on my 84 and I'm happy with them. They squeak just a little but it's not bad at all.

But I also went from totally worn out factory bushing's to poly. I felt it was an improvement. But maybe I don't know any better because I never drove the car with anything else.

 

I think the R-joints some of those parts use is fine. But some of those also have Delrin axial bushings at one end, and I wouldn't use those on a dare.

 

I was surprised out how much the components cost now. I did NOT go back in time via the Wayback Machine to look at the websites
and see if there have been price increases now that the competition is fading off into the sunset.

 

If I wanted to KEEP the rear control arms (largely for rear view appearance), can you think of a solution to create maximum articulation? And, eliminate "snap oversteer? For example, how much would JUST heim trailing arms accomplish? I bet SUPERPRO wouldn't sell JUST 4 control arm bushings. I wonder if there's some press-in Johnny-Joints or similar that would work -- in the control arms? And, in the trailing arms for that matter?

 

I emailed Super Pro here in the States. C&S Corvette out of Florida is the sole distributor. They get them to the other vendors.

I sort of figured that as C&S is who persuaded Super Pro to make them for the C4. (I spoke to the owner and other folks back
when I first found these and let everyone know about them).

With that said, I have been watching and they have some limited quantities back in stock. If you are thinking about it, today
would be the day to either p*ss or get off the pot before they go out of stock again.

https://www.corvettepartscenter.com/...ions/c4?page=1

there are vendors out of Australia selling them individually

https://www.ebay.com/sch/i.html?_fro...r+pro&_sacat=0

 

Without having done any actual measurements, my sense is that if you have hard poly in the trailing arms and camber rods right now, the majority of bind will come from the trailing arms. Ergo, replacing them with rod-end links would eliminate most of the bind. However, you get other benefits from replacing the stock camber rod setup (with or without hard poly bushings) with rod ended links: namely you get rid of the stupid eccentric camber adjuster and replace it with threaded rod ends that give you way more camber adjustment range and will never slip and change camber settings.

 

I wonder if there's some press-in Johnny-Joints or similar that would work -- in the control arms? And, in the trailing arms for that matter?[/QUOTE]
I'm sure you could find something could work. How practical it would be to machine control arm bores to retain the bearing is a issue. . IMO the camber rod has the most binding going on. The aftermarket kits also eliminates the alignment cams. Allowing precise adjustment by altering length.
My experience with snap oversteer relates to try to control rear body roll IMO relates to spring, bar, and shocks. Not so much control arms.

 

Another contribution into the thread for other folks, be aware that the 1996 dog bones are different from the other years. Prior years are aluminum, 96 are composite and I have read (but not confirmed) that the bushing size would be different.

Watch these

 

Johnny joints or those "R-joint" things Ridetech uses would probably work pretty well. The challenge is getting ones that are sized to fit the C4 control arms. I have no idea if they exist as off-the-shelf parts - seems unlikely, but you never know. That's a lot of trouble to go through to avoid the two obvious good solutions that are available right now: SuperPro or rod-ended links.

they are different. I have measured them. Took me by surprise!

 

I'll add one small bit of information about the superpro from my install experience. The rear ones are not a perfect cylinder. While it is a poly material the "movement" it allows seems to come from its shape... the superpro isn't a cylinder when pressed in. It's high centered and smaller toward the outside of the bore. With the sleeve installed it kind of operates on the same principle as a heim joint I guess. It's basically, and this is a drastic generalization, is like a football in a snug pipe. You can tilt around the ends but the middle is tight.

Obviously it doesn't and isn't capable of moving as much or freely as a heim joint but it does allow movement. I was able to "test" that on the bench with a screwdriver in the sleeve and the suspension component in the vise. You observed the sleeve moving with the screwdriver with force. The fronts which are completely cylindrical like a traditional poly bushing hardly moved.

Just a bit of information I thought people might find useful.

 

So guys, I want to make sure I have this straight. The rubber bushings on my ‘95 with 73k miles have some dry rot cracks on the visible parts on the front suspension. I would imagine the rear suspension has the same. So if I were to replace the entire front and rear, where exactly should I look to replace the rear with heim joints? In other words what links/arms should be replaced with an aftermarket heim joint design to avoid binding?

 

That is really very interesting! I'm glad you shared that. It makes perfect sense: the highest pressure on the inside sleeve is in its center, which helps to solidly locate the link from any movement in tension or compression; while there is less pressure on the outside ends of the inner sleeve, giving it more freedom to move around the center. I'm even more impressed with SuperPro now!

Two-Part Answer:

1. The links where we don't want old-school hard poly bushings are the camber rods (lower lateral links between the diff and the knuckles) and the trailing arms ("dog bones" that run fore/aft from the frame to the knuckles). In both locations, using either heim joints or SuperPro bushings will minimize bind.
2. If you use links with threaded heim joints in the camber rods, you get a lot more range of rear camber adjustment and eliminate the chance of slippage/movement of the camber setting.

 

It's nearly 5yrs since I converted to poly. I'm TRYING to remember how I visualized it working. At the time, I remember reading about trailing arms, how they work, and geometry differences in C4s vs C3s. In short, I'm trying to decide if the [large] lower control arm moves laterally out of it's up/down, hinged axis? In your explanation above, it seems likely -- as the effective length of the most perpendicular control arm "shortens". Is outer end of the control arm moving toward the trailing arm "mount", then back as the other arm "gets longer"? If that's happening, is that where you say geometry is changing?

Even with heim joints, wouldn't this still happen?

It sounds like the poly rotates around the cylindrical center metal bushings? With flex/compression, the control arm could remain in plane. (I'm picturing the trailing arms "stretching" toward the control arm as the "axle" rises/falls.) THAT ability seems a plus -- for control arm geometry/movement.

In short, I'm not understanding how the [poly] bushings rotate and "allow" lateral articulation. For instance, without the ability for the trailing arms to "stretch" in/out (using heim joints) would the control arm be forced into more lateral movements -- as it hinges up/down?

 

I'll add one more point of clarification, the poly shape on the inner bore of each rear component is a little different depending on location/part. So how it moves inside the part its pressed into is a little different as well. That's why there are several part numbers for the rear even though they're mostly all similar.

I agree though. I thought tweaking the bushing within the bore of the part its pressed in because its spherical-like instead of a perfect cylinder was quite clever and an easyway to get around the inherent stiffness of poly in that application.

You can see what I mean here for the rear compared to the straight cut front here. It isn't much but provided a surprising amount of movement so to speak.

 

Miller, thank you very much for that. That’s exactly what I’ll do when the time comes. When I raced circle track cars, the entire suspension, front and rear, and the steering linkage were all radius rods with heim joints. Not only did it offer full range and zero play, it was easy to dial your settings in.

Thank you all for the info. Great thread. I never would have known about the bind in the rear.

 

I'm having a bit of trouble exactly following everything you wrote here, but your last question that I bolded is correct. Think about it as you look down onto the suspension from above (plan view) and look at my crude drawing below. The trailing arms and camber rod form a right triangle with the car at resting ride height (not exact, but it's close). The black rectangles are the axial bushings (pretend they're black poly). They only allow free rotation around their axis, which is perpendicular to the link itself. If the link were not connected to one another, then swinging the camber rod would make it look shorter in this view, but it would always remain perfectly vertical in the picture. The trailing arm would always remain horizontal. But they are connected (through the knuckle, which I left out because I'm shitty at drawing this drawing this stuff). Therefore, when the suspension compresses, each link pulls the end of the perpendicular link toward its frame or diff mount and it's no longer a right triangle. The links are also no longer perpendicular to their bushing axes, and that's where the bind happens.

This is way more extreme than real life in a C4 with a few inches of suspension compression, but I drew it that way to make the point more clear.





The angles of the links would still change, yes. But heim joints don't have a single axis of rotation: they have full freedom of rotation around a single point, so if the links are no longer perpendicular the heim joints don't care.

Yes, around the inner metal sleeves.

The poly bushings have to flex to allow their inner sleeves to no longer be on axis with the hole bored in the bushing. Same as with rubber bushings. Only rubber is pretty flexible and creates minimal bind within the small amount of off-axis movement required. Regular poly is not very flexible and it takes a lot more force to force the inner sleeve off axis. That force is the bind. It adds to the force it takes to compress the suspension, and the rate at which it rises also rises the more suspension is compressed (i.e. it does not add a linear/constant wheel rate). It requires zero force to move a heim joint around it's center point in any direction, ergo there is no bind.

 

You understood me. If I look at the pivot point on the lower, back part of the rear wheel (using a still taken from youtube vid above), there appears to be almost zero room for the lower control arm to move laterally. (IOW...for the hub to move forward)

You mentioned some measurements in the .2" range. Because my rear wheels extend beyond the plane of the fender, I'm assuming the range of overall "articulation" isn't that much? Specifically, if in normal driving, the up/down movement of the control arm is, maybe, +/- 2" -- leading me to think that .2" lateral movement doesn't happen unless/until EXTREME body roll occurs? Because I have wider ZR1 rears, I'm considered the need for a bigger rear sway bar. Would that help reduce (body roll) hub articulaion -- making it harder to put the poly in a so-called "bind"? Conversely, would complete heim-equipped control/trailing arms allow MORE vs less out-of-plane movement?

My first thought is: SOFTER trailing arm bushings would all allow more stretch so the control arm stayed closer to it's up/down plane. Eliminating ALL "stretch" via heims intiuitively seems more likely to increase fore/aft hub movement. Maybe the lower control arm "needs" heim joints MORE than the trailing arm? To me, it seems RUBBER in the trailing arms with Heim control arms would be ideal. So, I'm probably not completely understanding.

 

Bind happens whether the suspension moves due to roll or left/squat. It just doesn't cause handling problems unless you're turning, in which case roll is at least part of what's happening. There isn't a ton of fore/aft movement, which is why rubber bushings work pretty well (they would also bind if the movement were a lot more). It's just that hard poly is a lot less tolerant of even a fraction of an inch of off-axis movement.

I don't think you need to worry about the movement in the context of tire clearance with your fenders. It's not enough in real life to worry about it. A stiffer rear sway bar wouldn't help because you'll have the same movement in lift/squat whereas a swaybar only functions in roll. And you'd be adding even more wheel rate in roll, which would only exacerbate the handling imbalance caused by the bind. So don't do that! Like I said, I don't think you have to worry about clearance.

There's nothing to make the rubber stretch in that way, though. It's going to move the knuckle/wheel around (toward the front of the car) the same amount regardless of which bushing/bearing type you have in there.

 

Same stretch -- but different compression/rebound? I give up. That's not intuitive for me. (No offense).

After watching Newman's vid, intuitively I can see heim's are best. That's not a fact, it's only a feeling. Your last statement leads me to wonder if/how the use of poly can be quantified? Is the issue any different that choice of tires...where one model is "mushy" and skids versus another that's "grippy" and (to some) a bit over-responsive? (While reading reviews, the term "twitchy" was given to one tire -- until they got used to it. Furthermore, that character might not be desireable? You said people who don't practice "evasive maneuvers" might benefit from sluggish tires -- to prevent over-reaction in an emergency. Is this somewhat the same issue? Is the use of poly more "dangerous" than the choice of tire?

I'm asking because I can see reactions to people reading this being anything from mild to extreme.....possibly too extreme?

For me, the rear kicked out once in a situation I did not vigorously "practice". It was when I still had rubber. That said, it wasn't nearly as bad as letting someone drive my vette -- who had zero seat experience. It was a mild/moderate "mistake" that created (what I call) oversteer. (If that's oversteer?)

I would assume that most/all Corvette owners know steering is WAY more responsive than the average passenger car. As such, smaller [steering] movements are likely to be delivered in "close-call" situations. It's not clear after 5yr-use of poly that my car is "dangerous". Hence my underlined question above.

Do you consider your content in this thread: observational feedback, strong-to-severe caution, or a reason for class-action lawsuit!?!?

What's the best way to directly observe real-world effects -- for current polyurethane users -- in a safe manner? To me, the answer might provide adequate "prep" for any sudden maneuver situation. Or decide if poly IS the "wrong" choice?