JB666

Not even sure what to call it, but, when I'm on the highway, at around 70-80 MPH (Passing someone, of course), if I hit a bump, the car feels like it wants to jump lanes.. I only have around 45k on the car(95), what could be causing this?? I've been thinking alot about the R&D Camber Brace, but, would it clear up this issue?

tempest

one question, is it when one tire hits a bump or both?

in either case, if it really is bump steer, your alignment must be really out of whack, or your steering rack is crooked or really off center. could also be loose tie rods.

i can hit some pretty nasty bumps on one side but i don't feel her jumping the lane.

i don't think the camber brace will help unless you have some unusually excessive flex in the frame.

hope you find the cause soon since losing your steering at 80 is not a pleasant experience.

bogus

bump steer is not uncommon... the transverse leaf spring is the main cause.

I just don't like the way they absorb bumps...

hence, my desire to get coil overs.

2dogs

Has it changed behavior?

Things that cause that:
Wide tires on uneven pavement
Bad shocks
worn sterring pieces
bad ball joints
low tire pressure

JB666

Thanks guys, I'll check all those things out!! I'm getting it aligned this Friday, anyways, so maybe that'll help. It's not like it jumps over 10 ft, but, I do find myself over a couple of feet if I dont watch it... It makes sense (the wide tire theory), but I just figured I'd be glued to the road, like I am on the side roads.. Bad front shocks could be a good possibility too, since they are still factory.......

Jeff

92PoloVette

If you're not seeing any weeping from the shocks and they only bounce once, they should be ok. Don't assume bad shocks just because it is still the original part. If I remember, your car has relatively low miles. Also, they could have been rebuilt by a previous owner.
:yesnod:

JB666

Your right, it has low miles, that's what was concerning me... But, I'll re-check tire pressure tonight(didn't take the car to work today). When it's aligned, I'll have my friend check the front end over, just to be safe...

Jeff

JB666

Ok, well I went down tonight, and checked tire pressure.
Front tires both at 28-29 PSI - put them to 33.
Rears were about 30- put them to 33 also.
This is the pressure they came from AFS with, so I was ASSuming it was right... Could this small bit make a difference??

2dogs

That will definately help!

Tell us if you notice any difference.

vetracer

I think you are doing the right thing by getting an alignment. It can make all the difference on a C4. Mine used to take my undivided attention to keep it going in a straight line. Now it just takes one finger on the wheel!


[Modified by vetracer, 12:13 AM 5/22/2003]

JB666

Ok, when I left this morning, and checked pressure with my good gauge, it read 32PSI COLD, on all fours... Took it to work, the 63MPH "vibration" and a lot of the bump steer were gone... Now It's at about 68MPH :banghead: . So, what I'm gonna try, before the alignment Saturday, is putting it up to 35PSI (cold) and see how that works out.. I think, by reading through the archives, that 35 is a decent pressure to maintain, and won't kill my ride.

Jeff

2dogs

Vibration:
side to side in the steering wheel or a vibe throughout the car?

Get your tires balanced while you are at it....

Mach85

Things that cause that:
Wide tires on uneven pavement
Bad shocks
worn sterring pieces
bad ball joints
low tire pressure
________________________________________ ________________

:iagree: I have a friend that this happened to he hit a bridge and wiped out his 93 Vette. He was ok. I would hate to see it happen to anyone else. I would have everything checked just in case.

mvitacco

J:

I have had a '92 and currently own a '95LT1. I always suspected some
roll steer in the rear and purchased a Longacre Bump steer gauge to
actually measured it.
======================================== ====
I don't know if this is true for 1st gen cars because the K member and
LCA are different so I'm talking about a 2nd gen C4 (91 and up).
======================================== ====
There is NO bump steer in the Front over the full range of suspension
travel. I measured this 4 times just to make sure, I'm talking 0's out to
3 decimal places over 2 inches of compression and 2 inches of rebound.
======================================== =====
There is a problem in the rear. Bump steer in the rear is actually called
roll steer. I measured about 65 thousands on the drivers side and .080
to .1xxx on the passanger side. That is a lot. I called Dick Guildstrand
and talked to Dick
======================================== =====
Guildstrand make a tie rod kit for the rear of the C4 that will get it
pretty close to 0 (.002-.003 close enough for me). What I called Dick
about was to ask him how my rear tierod heights can be different
from side to side by about 3/4. This is a non-issue because I simply
added more shims on one side than the oter. The only way that can happed is it the rear hubcarrier rotated. Dick said then can happen in service the
uprights can get "tweeked" he's seen worse.
======================================== ========
Now if you look at your rear suspension at the relation ship between the
4 parallel locating links and the rear tie rods, you can see that if those big
rubber bushings sompress the rear hub carrier can rotate, IF the tie rod
gets higher you get roll oversteer (not good), if the tie rod gets lower you
get rollundersteer (you can live with that). So the next item on my shopping
list is a set of heim jointed rear parallel links.
======================================== ========
Having said all of that, I taked to friends that I know who autocross these
cars and apparently this is common knowldege, these guys run 1/8 all
the way up to a 1/4 inch of toe in on EACH side to work aroud the issue
because in the stock classes you cant relocate stuff.
======================================== ========
What you mention in your email sounds like a alignemt, tire, or combination
of both issue, worn wheel bearings, ball joints, etc etc.
Get you car on a digital Hunter alignment machine have the front end checked
out and see how
wacked out it is, get it to factor spec and then see if you really have any
sort of a problem. STock C4 specs have a very large range (for Showroom
STock racing?) so I would keep things close to midrange or 0 for a daily
driver. Look at the tie rods closely and MEASURE the tie rod heights. If
you see noticeable difference from side to side in the front, they you got
somethng bent, but the bumpsteeer on the front of a C4 is for all practicle
purposes non existant.
Feel free to email me when you get the alignemt specs and wear parts
checked.
Also, what rims and tires do you have?
Did you go up in front spring rate?
Some people complain about the transverse springs, however they are well
designed, and isolated. Put it this way all the SCCA TCC Corvettes,
Corvette Challange cars, used the stock configuration springs, they may
be higer rate that you want on a street car. The design of the spring is not
your problem in my opinion all things being equal