I am one of these people with the Banski suspension that does not like my softer ride. I am trying to figure out how to firm it up. I even called Tom at Banski he told me to check the alignment which I am going to do.
I aslo just purchased QA1 DA shocks so I can dial in some firmness in the back.
My car went to hell after replacing my stock Z51 rubber bushings in the rear.
When I first purchased the car it was very firm and handled great. Now I am not happy with the looser ride. I am hoping it is not the frame moving around back there, I don't think that it is.

 

Interesting... I have an 84' Z51 with the rear end mostly polyurethane bushings now and I always thought the car felt a bit "loose" in the rear end...

 

Student racecars for FSAE competition have been using a pretty low-budget setup to validate torsional stiffness. https://deptapps.engin.umich.edu/ope...AE+Racecar.pdf
Worth mentioning is that the desired chassis stiffness is relative to the suspension roll rate. Other suggested reading is Race Car Vehicle Dynamics, Miliken & Miliken Just for fun reading, I'm not really understanding what the goal is with the OP but just throwing that out there.

 

Improved ride quality through increased chassis stiffness.From a few posts back....

 

I don't want to hijack the thread but my feeling is that GM knew what they were doing with the rubber bushings (slightly binding) not allowing full articulation of the suspension components.The Z51 cars had stiffer durometer rubber and probably binded even more than the base suspensions.
Polyurethane (which is what I tried first) will allow more articulation than the rubber. Then the Banski or similar heim rods ends give even more articulation than polyurethane. Hence the looser feel compared to the stock rubber. Please note I am not knocking the Banski product, they are great pieces but unfortunately it has changed my rear suspension allowing it to float and feel unstable under hard cornering and lane changing.

 

I agree that the intention of the rubber bushings is to bind, the argument would probably be that to get the same feeling out of the rear you'd need a corresponding spring rate change. The unavailability of a rubber bushing set poses a challenge with c4's with old and worn bushings.

 

Guys, in discussing the articulating suspension bushings (as opposed to subframe mounting bushings such as those surrounding the batwing bolts), it would be helpful to distinguish "binding" due to non-axial movement of the control arm vs axial restriction due to stiction (poly) or bonded rubber compliance (OE bushings). Usually when we discuss "bind," we are talking about the former. This happens when an axial bushing (which is designed for only plane of rotation) is forced to allow rotation in a different plane. In the rear suspension, this happens any time the suspension moves, because the upright (spindle) travels in an arc rather than straight up and down. As a result, the upright ends of the trailing arms have to move left and right as well as up and down; and likewise the upright ends of the camber arms have move fore and aft as well as up and down. The large rubber OE bushings allow this non-axial movement due to their compliance - it adds a little wheel rate because the rubber is elastic, but not very much (because the non-axial movement isn't that large). Urethane bushings are not very compliant for off-axis rotation, though. So they add much more wheel rate due to this bind, and the wheel rate they add is also very progressive, building in rate with more suspension displacement. This is why C4s with rear poly bushings tend to have more oversteer: they have more actual wheel rate in roll due to the bushings' bind. Rod-end joints have no bind because they are multi-axial: they allow free movement in any plane, up to the limits of their travel. So they add zero wheel rate.

All of that is very different from restrictions to axial movement. In that aspect, poly bushings are pretty good if they are installed properly. They'll have a bit of stiction, but it's negligible; and they will have almost no frictional resistance to axial rotation once moving (i.e., once static friction is overcome). In the axial plane, therefore, urethane bushings add no significant wheel rate. This is why urethane bushings work great in the front control arms: they only require axial rotation.
But keep in mind that we can't have purely axial rotation in the rear suspension, and the poly bushings add a great of bind to any suspension movement per the previous paragraph. The OE rubber bushings are different than urethane bushings: they are bonded to the inner sleeve and outer shell. So with axial rotation, the rubber has to distort, and wheel rate is added because the rubber is elastic. The amount of wheel rate is still small compared to the contributions of the spring, swaybar (in roll), and damper, but it's there. That added rate is also fairly linear, as opposed to the bind rate of urethane bushings in non-axial rotation. Rod ends, again, have almost no friction and don't add significantly to the wheel rate.

So it's true that, compared to OE bushings and especially poly bushings in the rear suspension, rod ends (like the Banski joints) will reduce the wheel rate somewhat. This could be easily compensated for with an increase in spring rate, or possibly just a bigger swaybar, if desired. OTOH, if the suspension feels "loose" or "unstable" or "floats" in transitional maneuvers, that's a different problem. The decreased rear wheel rate should cause the opposite of those symptoms! Something else is going on with your car, and I agree with Tom Urban's suggestion of checking your alignment before doing anything else. I'd especially be looking for rear toe out, which will quickly make a car feel the way you're describing.

 

Well I received the QuickTrick alignment system and just checked rear toe and camber. Toe looks to be set at zero. But camber is way off!
Right rear looks like it is -1.1degrees and left rear is -.3 degrees.
Would this cause my problem?
I am going back in to adjust the camber to 0 on both sides and then recheck toe again. I will let you know if I feel any change after adjusting everything.

 

Based on reasoning like this - found in multiple places - on this forum, I've decided to go with a full Banski rear set up and polys up front. The money is already spent and the parts are on the way to the builder.

 

I honestly doubt that's the problem, but you should get it set properly regardless and then see how it feels. You might want a teensy bit of rear toe in, actually. Check your batwing bushings and your halfshaft U-joints while you're under there (remember, your halfshafts are also your upper lateral suspension link!).

 

The batwing bushings look fine no cracks that I can see. The half shaft U joints are not that old I had replaced them a few years ago. I will still look them over again anyway.
This car is 21 years old but it never sees the snow and I can count on one hand how many times it has been in the rain. So the undercarriage is clean. I really believe that it is either the car needs stiffer shocks from the change to Heim rods or the possibility that I am feeling too much frame flex. Once I adjust the camber and I install the QA1 DA shocks (I did not go with springs because it is a factory Z51 spring and it is not delaminating) I will report back with my findings.

 

36 years ago when I redid the suspension of the '65 I had, I used a combination of OE rubber bushings and hard teflon bushings that I made from scraps/bar ends I saved at work. I made bushings for the sway bar links and for the shocks.

Fast forward and Tom is carrying these:

https://www.banskimotorsports.com/pi...ck-mounts.html

36 years ago I found out that removing some of the rubber deflection from the suspension components made them extremely fast reacting. The guy I sold the car to (not a neophyte corvette guy, he bought and sold them in the area) all but wrecked the car taking it home (I followed him). I asked him what that was all about and he said he forgot that it handled and reacted so quick. A twitch of the wheel would cause the car to change lanes and it wasn't set on the "quick settings" (at least my C2 had 2 sets of holes for the steering linkage, normal and quick).

I have acquired a set of the pin top mounts for my car to go in with the suspension and a set of Delrin bushings up front.

So we will see. I am also on a waiting list to get a set of the beam plates to snug up the C-beam from the ZF-Doc.

 

That sounds like a good plan.

 

 

I don't think this thread should affect your decision at all. The C5 has the same problems...only less so. I had a C6 and leaving a gas station or driveway diagonally, it still groaned, creaked and the roof popped. Same problem...only less so.


What should REALLY determine which car you buy, is which one you enjoy driving more. Drive 'em both...then decide.

 

Drive both before making a decision. The C4's frame is not a limp noodle to the average person. Hell I never even noticed the frame is wiggly until I started reading about it. I went up a friends super steep driveway with mine and I had it teetering on 2 wheels. I had the top off the car and I was still able to get in and out without issue while the car was teetering. The left rear wheel was a good 5-6" off the ground and the front right was just barely resting on the ground. I expected the door to jam, but it didn't.

Its when you get into road racing and really testing the limits of the car that you will instantly notice the structural issues. Some things you can notice normally though like the cowl shake. Most people just putter around in their C4 and never even notice the flaws.

Some swear by theses...

https://www.corvetteforum.com/forums...me-braces.html

...and others say they don't do anything. I would like to see a car with those rods do the same test that Tom did.

The convertible X brace supposedly works and seeing that GM used them from the factory i would imagine they do something. Too bad they are hard to find...

Same with the aftermarket X brace that R-D Racing produced, hard to find because I don't believe they are being made anymore but ppl liked it.

 

And even then, note that a C4 with a stock frame and suspension pickup points just won the NOLA Optima event. These cars don't suck.

 

You are correct, they don't suck. They were world class performers in their day and are still a force to be reckoned with. Clearly the body might shimmy and shake but it can hold its own!