Hello,

I finally got my car legal and on the streets after an 11 year hiatus. It runs great tons of power. I installed a complete new suspension as well. Except for the springs, they are still stock. It has new Continentals on it as well, that made a huge difference. The suspension is polyurethane and the shocks are new Bilstein all the way around. The car is bouncy in the back and it groans with hard bounces. It rides terrible. Doors rattle like you wouldn't believe. I expect it to be firm and a little rough on rough roads but this is so bad it upset my stomach after about 1/2 an hour. Anyone else have issues getting a good ride? Feels like a lowered mini truck.

 

What year, base model or Z51. With what you have it should not be bouncy per say unless you have too much air in the tires Groaning is most likely your rear suspension bushings. After sitting that long the groans and ride will get better with use.

 

Did you have a 4 wheel alignment done after you put this all together? Did you grease the poly bushings?

 

It's a base model. I did grease the bushings, maybe not enough. I have not had a 4 wheel alignment. But when I was driving it around before I did suspension and tires it was bouncy and vibrating. Did the suspension and tires and now the vibrations are gone but the groaning is really loud and the bouncing is not acceptable it's terrible and it's really defeating to put all this work and time and still have it ride like a bag of bolts. 4 wheel alignment is in the cards VERY soon. I found a corvette shop close by that will do it for $199.

 

Did you tighten all the suspension bolts with it loaded at ride height?

Possible you also installed the swaybar upside down. Post up a picture of you have one.

 

What Bilstein shocks did you use? Do they have heavy duty and regular versions and if so what did you choose?

 

I tried to tighten all the suspension bolts at ride height. But the new shocks and bushings would not compress enough get it at proper ride height before the car lifted up. Hope that makes sense. I got it as close as I could then tightened it all up. The first time I lowered it off of the jacks it was sitting several inches higher than normal. A quick drive around the block and some easy left and right turns and whole car settled right where it should be. I have had the car on jack stands since then for other things and I notice when I let it down it still sits high then settles with the first drive.

I will get a pick of the sway bars asap. I did take pics of the sway bar on the car and matched them going back on.

 

I ordered the Bilstein B6 front and back. That was all I could find when it was time to order. I think they are the heavier ones. I have the standard spring, NOT Z51, in the back and it does have a few small splits but nothing major. I mean like a few fibers have split off.

 

What cold inflation do you carry in the tires?

 

Tires are at 33.

I was thinking last night I would go back through and remove the dog bones one at a time and add grease to the bushings where they meet the mounts. I greased the bushings going into the dog bone but maybe there are groaning where they rub the mount on the car. That is where it sounds like it's coming from. I will also loosen everything and retorque at ride height and see if that helps. I am thinking now since I have some miles on it I should be able to compress the system to the proper ride height. On my truck I just set it on the ground with everything just barely loose and it went to the proper ride height and then I tightened it up, easy. I cant get to all of it that way on this car.

Here is a pic of the rear sway bar.

 

If all your bushings are urethane, then it doesn't matter whether the suspension is loaded when you tighten down the bolts that capture the bushings. The inner sleeve is supposed to rotate inside the urethane. The need to load it before tightening only applies to stock rubber bushings, because they are bonded to the inner and outer sleeves and work by twisting the rubber inside the sleeves. It's possible that rear urethane bushings is making the ride harsh. They do cause binding because they don't properly allow off-axis movement like the rear suspension links require. However, I seriously doubt they'd add so much bind that they'd cause the ride problems you're describing. I'm also sure it's not alignment or wheel balance or the shocks.

I think ChumpVette called it. It's hard to tell from your pic, but I'm pretty sure your rear sway bar is upside down. It has to do with the clearance between the frame and arms, not the center portion of the bar. The arms have kinks in them, and that kink needs to be facing down so the bar clears the frame. If you put it in upside down, it will fit while on the jacks, but when you set the car down the frame will be sitting on the arms and you will have exactly zero compression travel. That makes for an bad ride! You can probably guess how I know about this...

You can jack up the rear and pull a wheel off. Does the bend in the middle of the arm go up or down? Are there witness marks on the arm where it's hitting the frame? That will tell you what you need to know. Also, below are three pics of how it should be installed. If the bar is upside down, the bar will hit the shiny aluminum-looking piece above the swaybar arm in the third photo.

 

What does "I installed a complete new suspension as well" really mean? Exactly what did you replace?

 

I installed new bushings including sway bar and batwing ALL the way around. Installed new shocks. Installed new upper and lower ball joints in the front. Installed new outer tie rod ends on the front. Installed new outer control rod ends in the back. Installed lowering bolts in the back. Lowered it about 1". Looks great. Installed new half shaft U-joints. I did not change the front or rear spring.

Here is a pic of the sway bar before I took it off. I matched this pic when I re-installed it.

DMA Corvette here in Dallas has the car now for the alignment. He said he would drive it around and see what he thinks is going on with the ride. He had 2 other C4 in the shop when I got there. Plus a whole host of other vettes around in other various stages of repairs.

 

I wrote the below, then read Matthew's post about the sway bar hitting. That seems a lot more plausible since your shocks are new. If that's not it though, see below.

I know you said you replaced shocks, but you're describing how my car rode with bad shocks. Highway speeds on tilt-slabbed concrete would nearly bounce me out of my seat on each ridge. I know little about shocks, but:

• Is it possible the shocks were damaged on installation?
• Is it possible the shocks' travel isn't suitable for your car? I.e., could they have overextended or bottomed out?
• This seems unlikely, but could the shocks be defective, or could they have been damaged in transit?

C4s are pretty harsh in general, is it possible you just misremember how it rides? Mine is so rough on cobblestone I can't go more than ~5mph. And even on a slightly bumpy road there are plentiful squeaks, groans, and rattles. I have poly bushings, but I don't remember ride quality changing when I switched from the stock rubber bushings. It's normal for the car to not immediately go back to normal ride height after doing bushings.

Edit: Lowering it 1" is definitely relevant. You sure you're not hitting the bump stops? Maybe you could stick on a lump of Play-Doh and see if it gets smashed after a short drive.

 

If it looks like the pic you posted, then it's correct and shouldn't be hitting anything. I don't see any reason that the bushing changes should add that much to ride harshness - maybe a little, but not tons. Lowering 1" should not be a problem, but do verify you aren't sitting on the bump stops.

Ride harshness in a C4 is almost always related to the rear suspension, since we sit almost on top of the rear axle line. I think the next step is to jack the car up and support on the frame rails, then disconnect the rear spring only. Then use a jack to cycle the rear suspension through its full range of travel and ensure you have full range of travel. If not, start disconnecting things one by one to see which part is preventing full travel. I'd start by disconnecting the swaybar, then dampers. Beyond that, if you still don't have full travel, then check the trailing arms.

 

Has anyone suggested to inspect front and rear leaf springs for cracks/splintering? Any cleaner other than simple green will cause the springs to crack.

 

Hello,

Thank you for all of the great responses and help. This forum has been a life saver on this project. As soon as I get the car back from the shop where it is getting aligned I will let you know what he thinks as well and see where this goes.

Thanks again.

 

Did you use the correct torque specs for poly bushings? That could cause the bushings to be locking the “travel” of suspension parts.

 

Hello,

I got the car back from the corvette shop today. The alignment is now good. He gave me the print out showing how far out it was. The back was pretty bad. It drives straight now. He even complimented me on my work throughout the car and said everything in suspension was correct. He said he drove it around and said the ride is a little harsh but not out of the envelope of normal. He said my spring is showing some small splits but nothing major and a new #228 spring might help it smooth out some. He also said I could take off those Bilsteins and go with a standard AC Delco which wont transfer every pebble and bottle cap you touch right to your butt. But he said the new bushings cause a harsher ride and rubber is really not available so this is what you get. He did say there are supposed to be a new type of urethane busing coming out that is about half way between what there is now and rubber.

Guess I am just used to newer cars and my 2016 truck. It's been a long time since I drove around in a 25 year old car for any length of time.

 

'84 Z51 with all poly, Heimed rear, zero rubber, lowered and street driven. Stock, was reportedly the roughest-riding Vette ever from Chevy and had a 'happy' butt; bouncy.

Per advice during a chat with their engineer, I had Bilstein rebuild the stock shocks using 'Challenge" specs years ago; cured the bounciness. Car is rock solid and ride is firm, but not bad at all. Don't recall the PN, but aftermarket Bilsteins weren't okay, and two sets of Monroes leaked in short order.