Hi,

I recently replaced front shocks because one of the gears was broken on a FX3 controller (I still have the old shocks for possible rebuild). I could have replaced a single shock, but decided to replace both so that they would match.

At the time, I did not ask mechanic to also replace rear shocks. I feel like that may have been a mistake, but I do not have too much money burning a hole in my pocket.-)

The car rides great, has no issues with handling or comfort on smooth roads. However, even the highways are not pretty smooth where the car is used (overseas). Since the tires are so wide, if there is an inconsistency in the road surface, the car becomes a little scary. It is not so much the pot holes, but the level of the asphalt may change in the width of a 275 series tire, or road crown, or ruts due to truck traffic etc.

I feel I have to brake for such, where as I feel safer those in a compact vehicle with 185/65 R 14 tires at a faster speed. That said, my tires are two year old Kumho MX series (purchased new). I am running them 35psi, partly because I do not want them to flat spot when parked for 11 months out of 12. I only drive the car in July.

I was reading 101 Projects for your Corvette by R. Newton, and he says rear shocks are more important for ride control on the Corvette. That said, I looked at reviews when Corvette was introduced on Popular Science etc. and they dinged the C4 because it was uncontrollable at non smooth road surfaces.

I have tried Competition mode on a slow cobble stone uneven street, and no creaks, suspension and body are tight as a drum. On the street, I am now defaulting to Comfort only as Sport is overkill.

The car is all original, it was sitting in customs from 1993 till 2008 when we bought it. Customs are like %200 of retail price, so the guy who used it had fake plates. Because he never registered the vehicle officially, we had to pay customs on the price we paid in the auction.-)
Since the oldest car you can import is about 3 years old, this is perhaps the only 1989 in the whole country.

It has original 30K miles.

The reason I am asking is that Bilstein has a reputation that it will last indefinetely especially with low miles, especially in Mercedes community.

In my case, it may be a better idea to scrap the FX3, and just get Gabriel Ultra's for $100 or less, or Monroe Sensatracs. The road surfaces are simply not made for this type of supercar.

C4ZF6nut

 

The problem is mainly your highly uneven road surfaces. You could try an inexpensive non-performance shock absorber and change the springs for softer ones, but you might derive more of a benefit by installing tires and wheels that are not as wide and running them at lower than 35 psi. Wide tires will grab at uneven surfaces, the relatively stiff springs on C4 Corvettes amplify this.

Thomas

P.S. When I ran 315 tires on all four corners I also noticed that my car became less stable in a straight line on roads with rough surfaces - it wanted to dart from side to side. Of course it cornered fantastically.

 

When you replaced your front shocks, did you get FX3 shocks?

Shocks do "wear out" after a period of time, even the FX3 versions. While they are adjustable, they do have dampening oil and are gas charged.

Bilstein in the US does offer a rebuild service but they shocks are sent to Southern California. They do offer custom re-valving for performance use. In fact, the custom valving (called Moracca) was designed by a CF members.

If you did not install replacement FX3 shocks, the FX3 system will not be working. Any error codes in the system will automatically put the system into Tour mode and no adjustment at the selector switch is possible.

 

I do not know if the shocks needed replacing, but sending parts from the US, I simply bought used controllers from a low mileage car (solenoids) and new front shocks and shipped them overseas so the local Corvette shop could install them. They noticed that the solenoid was not attached to the left front shock and the gear was broken. They could have alerted my father that the rear shocks needed replacement, but they did not.

When I drove the car, there were no error codes, and there was a difference between competition, sport and tour modes.

When I was purchasing FX3 front shocks, I remember a fellow who sold a set of Gabriel Ultras (which were going new for $100) for $15+shipping. I wish I bought the Gabriel Ultras....and disabled the FX3...unless the replacing the rear shocks would bring some controllability.

I have Gabriel Ultras in my older Mercedes and Honda vehicles, and they are great over rough patches of road. That said, those cars do not have as stiff springs. The Mercedes has springs softer than 450SL-380SL-560SL (73-88), but the same suspension. Honda has full double wishbone suspension like the Corvette, with polyurethane bushing kit which made the ride very rough when installed, but either it is getting softer or I got used to it (Energy Suspension). I probably could hit 100mph with the Honda, and barely lose control on the same surface, which is scary at 50mph with the Corvette.

I also was planning to install the Corvette, Prothane polyurethane suspension kit, but it probably will make the problem worse.

C4ZF6nut

 

The chances are that the rear shocks are worn out given your description of the handling issues. As long as you have spent money for the front shocks, it would make sense financially at this point to replace the rears. I am a fan of the FX3 Selective Ride Control (had it in my old 92 convertible) and once you get an understanding of how the system works, it is (was) a good design. IIRC, Bilstein originally worked with Corvette engineers to develop this system utilizing a similar system that appeared in a couple of Ferrari models.

One other thing to consider is replacing all of the sway bar bushings and end link bushings. There are polyurethane sets you can get that will help with handling and reduce body sway. Poly bushings in the sway bars only should not make a big difference in ride comfort. The trick is to lube the sway bar bushing with the proper grease and to follow the install instructions closely. It's when you start adding poly bushings in the control arms and shock bushings that the suspension can become very hard.

Your ride characteristics you are experiencing are not uncommon with Corvettes and wide tires. Heavy traffic on roads will cause ruts to form and the wide tires have a tendency to "follow" the ruts. Sometime experimenting with air pressure can help as can making changing in alignment specs. Maybe a little less negative camber and an extra degree or so of toe-in can make a big change.

It's difficult to make a true comparison between European sport coupes and a Corvette especially when comparing suspension design and setup given the differences in US roadways and those in Europe.

 

Follow up

My car turns out to have excessive wear on the left front wheel bearing. I was surprised as this is a low mileage (30 000) sample.

I also have some doubts on Richard Newton´s 101 projects book where he says front bearings rarely go bad. He also recommended Timken bearings which I purchased at Rockauto. Of course people who use them say they go bad after two track events.-)

C4ZF6nut