I have a 91 coupe 67k miles with FX3 new tires Kumho asx 275/45/17 with 32 psi cold air pressure. FE1 standard suspension spring rates. Shocks and entire suspension is all original from what I can see. The car seems well maintained and I have been upgrading things over the winter the interior will be done today I trust with fixing a small wiring issue and working on the spring tracks and motors I think I have enough parts to button that all up or get close if nothing else.

Now the real question, not on all roads but many sections of the local interstate around New England it just does not have what I would call a secure road feel above 65 mph. It just feels nervous with a background slight vibration buzzing feeling. I do think the FX3 parts are working and ok and can tell some difference between the setting especially over 50 or so. I had an alignment done and what I believe to be a quality balance job when new tires mounted a month ago. It was a lot better after that. This was done by a local GM dealer that I have been doing business with for at least 10 years and a small town where everyone knows everyone else so the usual rip types don't play well here the news travels way too fast..LOL..

I am up for suggestions as to where to look or if this is normal i bought a car that I will not like driving all that much. I bought it to be an interstate cruise machine and this is a bit un-nerving. I am sure they checked the bushings ball joints wheel bearings etc as i requested it at the time of the alignment and all was reported ok. If there was any problem they would have gotten the repair so an incentive to make sure all is ok. As a side note when the tires were balanced I had them use stick on wheel weights so as not to have any on the outer wheel edge but this has to be very common I would think..

Any ideas???
Dave

 

The whole idea behind the firm Corvette suspension is to maximize cantact and retain balance on the road. That "nervous" feeling you describe is actually the opposite of nervous.

In say, a luxury car, the suspension is designed to keep you from feeling the road. The spring rates are slower. So when you go over a bump the car kind of floats. However, at higher speeds when for example going around a curve, the body will lean, or roll if you will. On the Corvette, you do not get this roll because of the stiff suspension, the car stays flat and balanced. The spring rate is quicker so as to maintain as much wheel to road contact as possible. This also keeps the weight of the car balanced and over the suspension as opposed to being thrown from side to side. The price for this performance is the the driver gets thrown from side to side. The stiffer the suspension, the more you will feel the road, this is the nature of performance driving and actually, at higher speeds, trust me, you want to feel the road.

 

Possibly I did a poor job of describing it. It feels more like a high frequency vibration rather that a pitch force or pulling some g forces. I think what i might do and see if this seems sensible, there is a local Corvette club in my area and possibly have either a current or past C4 owner take it for a ride and get a driving impression from that. A is it normal or B what might you look at. I have driven tons of sports cars and the good ones are very firm and silky smooth at the same time, a Ferrari does not do this and I have driven several. If I did not know better I am going to bet on out of balance rotors shocks with low speed damping shot or a wheel bearing issue that while not really loose has some noise in it that gets transmitted back to the wheel. I am tending towards the shocks for only 1 reason in that if I set them to full stiff it gets less busy and more firm and planted, almost feels like a wheel tramp..
Dave

 

The FX3 shocks are gas charged with an oil fill. The gasl works to help prevent aeration or foaming of the oil. Bilstein deliberately added more oil than usual to allow for seepage. If you have wet oil on the shock body, you could have sufficient leakage that would cause the shock to feel soft in spite of feeling the difference in the three settings. BTW, the FX3 shocks were developed by Bilstein using a Ferrari design.

The FX3 system is designed to have some degree of overlap in the shock stiffness based on vehicle speed (the VSS at each wheel is used by the FX3 controller to adjust the shock stiffness within each of the 3 positions of the selector switch). For example, the Tour setting at 70MPH is actually stiffer than the Performance setting at 25MPH.

The FX3 shocks can be rebuilt by Bilstein for about half the cost of buying new ones which run $200 each. Bilstein can also modify the FX3 shocks for a custom valving for things like autocross or track days.

Vibration at highway speeds can be a number of things, warped rotor, bad u-joint (there are 6 of them ) a driveshaft or halfshaft out of balance, worn front or rear wheel hub (bearings), or even a wheel that is not true. The hubs are not servicable and are replaced as a unit.

 

Check to see if your rotors are out of balance. Earlier rotors have a weight sandwiched in between the vanes for balance. They are a kind of V affair, and sometimes theyre are two in a vane, or the vanes are machined off in an effort to balance them. I heard a noise that sounded like my wheel impacted a rock, and the rock got caught in the wheel somehow, and for a tenth of a second, there was this wierd noise. Well, about a year later, I pull everything apart, and there's a ding in the inside of the wheel, and the keeper for the rotor weight is in a vane. But no weight. I didn't know to look to see if the ding and the keeper lined up, so I sort of surmised, and no way to see if that was the lug position.
It will feel like you have a tire out of balance, and the balances all check out.
For the nervousness, if the car has been lowered, or if you are out of gas, it would be more pronounced.

 

Car has not been lowered as far as I know though have no idea how many have owned it before me bought it november last year. Saying that I can hit the front spoiler on a gas station ramp if not careful to take it on a diagonal but looking at pics of lowered cars I have a lot more clearance between the wheel and fender lip than those cars. Fuel load makes no difference at all.

I am a machinist among other things build one off parts for vintage race cars and have loads of dial indicators etc. I think maybe I will put the car on stands high enough to pull the front wheels to start and indicate the wheels rotors etc for runout and the bearings for play while at it if not that and tie rods ball joints good as far as i can see it can only be two things in the front at least. Those being something out of balance or the shocks are shot. I gave the suspension a bath this afternoon in anticipation of that and will keep an eye out for shock oil though everything was so dirty there is no way to tell what grease came from and if the shocks are really low they could be shot and not drip either as no more oil to leak.. I have to say I am really not up for shocks at this point in the economy.. I did check into the rebuild cost and unless it has changed in the last couple of months it is 150 plus parts and 99% of the time you get a new shaft that is not part of it and come out at the same price as new with only a 90 day warantee..

At the end of the day it could be the crappy roads in SE Connecticut but we will see. I can not believe that Calloway would go to all that trouble to build cars that drive like this one..
Dave

 

my friend has a 1990 vette which made a loud humming noise with a vibration. It was found to be that metal bar from the rearend to the transmision (the bolts were not torqued) after the car had a clutch put in. He took it in for wheel balancing, checking the rims, u-joint inspections.

 

Alright I get it. What threw me was that you said it didn't do it on all roads just some roads. But I know what you're talking about. There are certain road conditions that bring out troubles that other roads will not. I would have the tires rebalanced first. Sometimes after a little road time a rebalance will zero things in. An alignment will help as well, these suspensions will notice if something is off by a degree. Mine is smooth now after aligning and new tires, but alas I say smooth in the relative sense. Afterall, it is a Chevy.

 

Regarding the car feeling 'nervous', I would suggest the following:

1. tire pressure -- If I recall correctly, some C4's with the same tires all the way around (i.e. yours) actually called for 35 psi cold all the way around. We run 33 psi cold and the car feels great 65->90 mph, but our 94 has 255/45 Front and 285/40 rear with new Bilstein FX3 shocks from Eckler's.

Have you tried increasing and decreasing the pressure to see if it makes any difference?

2. Alignment -- incorrect 'Toe' or 'Camber' could cause the car to feel unsure of itself -- and even if you have the before/after printouts, if not set-up correctly or out-of-calibration, or the 'mechanic' "knows better" or just had a 'bad day', the printouts don't always tell the 'truth'.

Our 94 is set-up with a total front toe = 0.08 degrees and rear toe = 0.06 degrees, and front camber at 0.1 at each front wheel.

Also, 'within tolerance', may not be right for your car and 'butt'.

Further, failure of the 'mechanic' to check the ride height or 'jounce' the car 3 times before checking the alignment CAN make a difference.

There are also different recommended settings based the type of driving -- you 'butt' may be more sensitive and need a more 'agressive' setting.

Also, a little bit of extra Toe-in can compensate for slightly worn suspension parts.

Suggest checking out this website and comparing the alignment results: http://www.vbandp.com/instructions/h...ruct/align.htm

 

I am running 33 psi as well..
I am reasonably certain the alignment is correct to the specs provided in the link above I used the advanced street settings but left the toe the same as stock after reading it might wander or pull on uneven pavement at 0 toe. We have a lot of that around here..LOL Did a little road test the afternoon on I95 this time with the roof on and windows rolled up. Southbound had zero issues northbound a tiny bit but not nearly as much. Shocks set to full stiff on the FX3 the best setting either direction ran it up to about 75-80 very breifly and firm but good still not what I am looking for. To the FX3 owners what is the life expectancy of the shocks?? Obviosly the roof on means a lot of what I was feeling at least to me is flex in the chassis.. and the roads suck here as well LOL.. If it is shocks not sure I am mentally ready for 900 bucks worth of shocks for a street car saying that the HD or standard shocks are a third of that. Another question for the FX3 guys is the firmest setting firmer than the hd or sport non FX3 shocks... Well a potentially worn out FX3 shock at 67 k miles. I have to say I love the concept as in town and on bumpy roads the soft setting is nice but over 40 full firm is called for on any decent road. Any and all opinions welcome and appreciated.
Dave

 

Sorta OT... but I believe it was from the Porsche 959 program, not Ferrari. Though Ferrari did also use this setup on some of their cars. I believe after Corvette adopted it though.

 

Your running 33 psi.

Have you tried 35 and 30 to see if any difference?

On the life expectancy of FX3 shocks, not sure, but many have issues in the 50k-70k range so you might be near the end of their life (however, ours which has 90K had no leaks, but did have broken gears, so they might last a bit longer).

You mentioned 'believing' the FX3 system is working correctly, but are you sure?

Does your DIC have a 'service ride control indicator' light and does it illuminate for a few seconds after the key is turned on and then go off (no need for the engine to be started)? Unfortunately, some folks have removed the bulb to 'hide' the problem or to ignore it.

Also, do you hear or feel each shock's 'actuator' (motor on top of shock) do its 'little dance' (rotates one direction, then the other, then settles in the middle) when the key is first turned on (engine does not need to be started)?

Lastly, have you carefully removed the 'actuators' (read how to first or ask) to verify the shock gear and the actuator's nylon toothed-gear-engagement piece is not cracked or damaged? BTW, rears will require shock removal to do this inspection.

Even though most of the time when the gear or actuator are damaged, the FX3 computer will store a 'code' and disable the FX3 system. However, occasionally, the gear may be damaged, still operate and NOT throw a code, albeit likely not setting the shock equal to the others.

 

Will try a couple of pounds less air and do not have any codes for the FX3 system. I suspect it works as when changing a setting the cornering changes pretty dramatically and speeds over 60.. The light does come on when you turn the key on for a few seconds. Possibly I am not used to the 45 series tires so it is a new feeling rather than something wrong. The only other thing I can think of is there is some runout in the wheels or tires. The wheels have no road rash at all and no signs of scrapes or dents anywhere and these new tires are much better than the old ones as far as ride and handling.. If there is no runout or loose wheel bearings loose suspension parts i can only think of 2 things to do. First have the wheels balanced on the car and if they need a lot consider changing the rotors as they are the only thing that could be out of balance if the wheel checks good by itself. Second would be get at least a new pair of front shocks and see if that makes a big difference.