Bouncity Bounce Bounce???

[Ludigdrums]

Every once in a while I get a very strange bounce while I drive. Especially at slower speeds. Even on smooth pavement and I noticed it on the Dyno while getting an inspection. My mechanic said something about it.

Here's the thing. I've had this problem since I got the car, and since then I've changed the following: Complete Offset Trailing Arm assemblies, w/new rotors, New front rotors and Calipers...Full 4 wheel alignment, Brand new custom 18x10 wheels w/brand new tires.

So, I know that the springs and shocks are relatively new, 3-4 years old, but only a few thousand miles on them.

Any ideas?!

Thanks!

- Jeremy

 

[Bob_K]

Mostly just thinking out loud here, but I'll give it a try. If it even happened on the dyno it I don't think that it's suspension related, since there should be nothing for the suspension to react to. Almost sounds like a something is way off balance. If you had this before you did the work, I'd guess a halfshaft because you didn't change them out, but from what I've read they never balanced them, even at the factory. I guess maybe if there was a large enough chunk out of one or if a piece of cement or other heavy debris became attached to one that may do it. It will be interesting to see what some others think.

 

[Ludigdrums]

Thanks for the thoughts Bob....

I forgot to mention, I had the half shafts redone by a local Corvette shop w/new U-Joints. I also put in poly bushings in the strut rods. The only other thing I can think of is I don't have a spare tire...maybe the lack of weight sometimes causes a weird bounce? Doubt it!

Keep 'em coming...thanks!

- Jeremy

 

[76okievette]

Just a guess but what about the body shock mounts and the differental mounts if they are worn out or missing you could be getting the body boucing on the frame????

GO SOONERS

 

[Bob_K]

I don't have a spare tire either but I have never noticed a bounce. Then again, I probably wouldn't ahve since my suspension was in such sad shape before I started the overhaul.

 

[vettepilot]

Every once in a while I get a very strange bounce while I drive. Especially at slower speeds. Even on smooth pavement and I noticed it on the Dyno while getting an inspection. My mechanic said something about it.

Here's the thing. I've had this problem since I got the car, and since then I've changed the following: Complete Offset Trailing Arm assemblies, w/new rotors, New front rotors and Calipers...Full 4 wheel alignment, Brand new custom 18x10 wheels w/brand new tires.

So, I know that the springs and shocks are relatively new, 3-4 years old, but only a few thousand miles on them.

Any ideas?!

Thanks!



Does this occur shortly into the first drive of the day, or is it occurring at any time. I was thinking flat spot on one or both of the rear tires, and since it occurred on the dyno that eliminates anything in the front end.
I wouldn't think it was a balance problem in the half shafts because of the relatively small diameters of drive shafts, compared to large diameter rotating components (such as the tires), it usually takes more RPM to produce noticeable vibrations, and you stated that it's more noticeable at lower speeds.
I would start by taking a good look at the tires. Belt separations, sidewall deformations, unusual tread wear and or tread deformation could be signs of something internal to the tire casing is not right.
Other than the tires, I can't think of anything else that would give you a "bounce". I can think of other things that would cause vibrations, but bounce is as you described the condition so that's where my thoughts were confined to.
Keep us posted on what you find, this is interesting.

vettepilot

 

[JohnZ]

If you have a composite rear monospring, it's probably the rear shocks; with that type of spring you need shocks that are specifically calibrated with a higher level of rebound damping to avoid the "bouncy-bouncy" syndrome. VBP has several types of shocks calibrated for that application, as they sell lots of the composite springs to replace steel ones.

 

[tom102]

Bounce

Have the shop check the tires for a a belt seperation, this will cause the symptoms you described.

 

[Ludigdrums]

Thanks again for the replies...

This is the thing....this happened before the new wheels and tires and everything. I had a complete different set of wheels and tires and had the same symptom.

I have the steel spring.

One thing I have yet to get to, is the front end of my car sits real high. Maybe that's causing some problems. Check out this thread http://corvetteactioncenter.com/forums/showthread.php?t=48972

Again, the tires are brand new, and balanced real well.

This is a tough one because it seems to be random. The only thing being consitant is the slower speeds, just going down the block.

Thanks for all your suggestions so far! Keep 'em coming!

- Jeremy

 

[Bob_K]

Just a sec, racking my brain. Shouldn't take too long...not much there. Hopefully by morning I'll either come up with something good or at least something that sounds good. It makes sense that if it happened on the dyno it wasn't front suspension related. A dyno should be a smooth ride though I would think (never been on one myself), so I think that should rule out suspension all together...meaning it has to be a moving part. Here's a (silly?) question: where is the bounce (front, back, one side) and does it just go up and down (front and back) or left and right? Might help narrow down the culprit.

 

[Ludigdrums]

It seems to feel like it's coming from the back, and it's just a straight up and down bouncing motion. No side to side or anything. What's the weirdest thing, is that it is not consistant. I remember when I was first looking at the car, and I drove it to my house, and as I turned the corner on my block, I first noticed it. It doesn't happen all the time either. Can't figure what it could be!

Don't know if this helps, but I know that the shocks are all Monroe Sensa-Trac. They were put on by the previous owner a couple of years ago.

Thanks once again!

- Jeremy

 

[VRGSVET]

I have the same problem. I thought it was due to worn out shocks/springs. But, I recently had all the suspension bushings replaced along with new AC Delco shocks and a new rear spring (steel) from Mid America. It seems less noticeable, but not completely gone. I just figured it was due to the unique rear suspension set-up with the tranverse spring. I'm guessing that if I got stiffer shocks, like the Bilsteins, or equivalent, it would go away. It doesn't bother me that much, though, so I'll leave it alone for now. I'm curious if someone does have a solution, though.

 

[Ludigdrums]

I'm glad to hear I'm not alone. Maybe it's the white paint?! ;-)

- Jeremy

 

[wishuwerehere82]

I have noticed on my '82 that one of the factory aluminum wheels is off center. That is, the hub hole is not centered in the casting. I know you said you have new wheels but if the center is off, then at certain times after turns both wheels will be symetrically at the same "Off" center. and will start hopping.
Yes, it seems like a dumb thing to happen when the wheels are supposed to be machined symetric with the center hole in the CENTER, however, that is the case. Balancing can fix the balance of the whole tire and wheel, but the thing can still be loping along and is a lot more noticeable at low speeds. I noticed mine was off center while on the Dyno.
Believe it or not!

 

[wishuwerehere82]

P.S.

I also have Sensa-trac shocks and they don't dampen much of the small stuff out. There are better ones out there and we probably should spend the money and get them.

 

[Robin7TFour]

Pete, i too have sensa-trac shocks on my car. came with the vehicle.i thought i was just being critical on how my vette rode,now i see you have the same issue.
guess ,shocks will be on the list.

robin

 

[Ludigdrums]

I think we may have found the culprit!!! I'm excited to find out whether or not this is the case. I do not, however, after all the recent purchases, want to spend more $$$ quite yet!

Thanks for everyone's responses, if anyone has anything else to add, please do!

- Jeremy