My 1990 Z51 FX-3 car has leaking shocks that aren't working well anymore. It seems like a good system if everything else is OK - convience of adjusting from the cockpit instead of crawling under the car. What are the options for replacing them? I know I can buy new ones for about $200 each or maybe contact Bilstein and get them re-built for a little less. Are there other options or improvements I can make? I use the car as an almost daily driver and will do several track events per year.

 

I found my answer. Thought I would share info for other new FX-3 owners. Bilstein will rebuild and revalve with much improved performance over stock set-up. A new prom and selection box is also available that improves the adjustability and reduces the speeds required to get valving changes. Cost= $200 for prom and box, ~$100 ea for rebuilding and revalving shocks. The revalving and new box settings were worked out with Solo II competitors, etc. Hope this helps someone else too.

 

That's good information to know!!!

Also, how "modified" is your 70 Mach I? I used to have a 70 Boss 302, and two 69 Mach I's. The Boss and one of the Mach I's were totally stock, but the other Mach I, I had pulled the stock 390, and replaced it with a 427 side-oiler with a dual-4bbl intake.

 

$100 included revalving and rebuilding, and that was if it needed everything. For shocks in "good" shape it could cost a little less. The guy I talked to at Bilstein was the one who did all the modifications to dial in the solo II cars. He told me that Chevrolet left a lot of performance on the table with the original valving.

 

Much appreciated, thanks for passing this on.

Who's the contact at Bilstein for getting this done, and how long does it take?

 

There are two ways to do this.

First: (and cheapest) is to send your OEM shocks to Bilstein and have them rebuilt, as posted above. I did this about 4 years ago and so far have been very pleased with them.

Second: IF you buy the replacement shocks from Bilstein, they have a Lifetime Warranty on them. They will re-valve them for you, and the warranty is still good. The only reason I mention this is "How long will you have your Corvette?" I plan on keeping the C4 until it fades into fiber components. I can get multiple rebuilds out of them.

Just FYI.

 

Joe90,

How long do the shocks last between rebuilds? I figure it would take 2 1/2 rebuilds to pay for the new ones. The new ones also have the stock valving, not the revised performance set-up, so they would have to be changed at $50+ ea. Did you get your shocks re-valved or just rebuilt? If you have the valving changed how do you like it? It sounds like the prom is also helpful because it changes the speeds required for the shocks to change within settings as well as adds extra settings. Did you do that too?

Thanks.

To answer the other post: Call Bilstein at 800-537-1085. They are moving facilities so may not be able to do them until some time in september. I have to wait also. The contact is Bill Hendorf (I think that is how it is spelled).

 

Thanks for the info i have fx-3 and they need rebuilt i will give that revalving a try :bs

 

I have yet to pull the shocks to check them...should be sometime in the next few days. Something just doesn't "feel" right....you know how it is. I think mine might be leaking, but am not sure yet.

It has been about 4 years since I had mine re-built. They valved them at Sport, 80% locked & 100% locked. I got the new controller and had some interesting things happen on the first few outings with the new set-up. I took overall FTD's for starters for the first 5 events I was at. I also had some photos taken of my car along with others at the events. When comparing shots of my car in a corner compared to others, there was a dramatic difference. My car was flat, virtually zero body roll or nose-dive under braking. All the others were very pronounced in both those categories.

I had to change the controller because they upgraded my shocks to the newer style. The older shocks turned MUCH further from stop-to-stop. The new chip changes the envelope the shock controllers operate in.

The only negative part about this whole thing is the ride is a little harsher. Take yours around in "Sport" mode all the time and see what I mean. I didn't mind it all that much, it is still a LOT softer than my '86 Z51 was!!! But...the girlfriend didn't approve too much.

When I need them re-done, I'll get new ones with the "Lifetime" warranty on them. I'll never let this car go, so in 15 or so years I'll more than pay for them. I'll keep the OEMs and have them re-done to put on the shelf, though. That way, if anything happens I can always pull the spares and use them until the others are finished. When racing, spares are always an important part of your traveling parts warehouse.

 

Joe90,

Thanks for all the input. You are right about spares. I do run my car in sport mode all the time anyway, because it feels like the z51 springs overpower the shocks in tour setting. Besides, my shocks have 90K miles on them so they are gone anyway. It sure sounds like the revalved shocks with the controller are the way to go for any type of track use.

I read your list of mods and wondered about the single mass flywheel - how much additional noise (if any) do you get compared to the dual mass? I am trying to make some other decisions regarding my choice in motors too - I have many SBC parts with older style 4340 cranks and JE pistons, good rods, road race pans, etc. I've been thinking about running either a 383 or 400 shortblock and changing over to a single mass flywheel at the same time. Is the single mass flywheel with the ZF OK for a 90% street car?

 

2many, you would make a wise choice having your FX3 shocks revalved. They were originally used in the Corvette Challenge, but using much different valving and more agressive maps for the black box. Talk to Bill at Bilstein about your situation. I worked with them about four years ago to develop a valving set up that's perfect for a-x, street, and with bigger bars and agressive bushings, great for track events. There are some maps for the controller that will give you a wide range of adjustability.

BTW, your "Z51" springs are base springs in a '90 FX3 car. (unless they were changed by you) So they are not "overpowering" the shocks, it's just that GM mandated such wimpy shock valving. If you have Bilstein valve them using the "TM" valving, your car will have very minimal front end dive and rear end lift under braking.

There *was* (maybe still is) a plethora of posts early on in the Forum's existance, in the archives. Check your "search" function.

 

http://www.corvetteactioncenter.com/tech/fx3.html

 

DO you have these installed yet if not when you get them on please post as to how they ride and perform

 

h rocks,

I'll try some searches to see what I can find. I didn't know that GM only put in adjustable shocks and called it a Z51! I did look at the bars and the front is definitely not 30mm. Softer springs are OK I guess as long as I put in bigger bars. The wimpy shocks don't cut it and almost as bad are the changing valvings that will occur as you are slowing down for a corner on the track. The worst time for the shocks to soften up I think. Anyway, thanks again hy rocks for the shock info, and the alignment tips. If anyone knows of the previous threads to look at, please let me know.

 

2many, your car can have the Z51 option, along with FX3 and FE7 (I believe) and it will still have the base springs. If you do not have the FX3, but *do* have the others, then you would have the stiffer springs and larger swaybars. A straight Z51 car (no FX3) does not have adjustable shocks. Are you confused yet?? Anyway, I have done a lot of study on this setup, and again given the proper valving and programming, it's a sweet system. One of the earlier poster's asked if I had actually revalved my shocks and did it work. Yes, of course I have, and as previously noted, it works exceptionally well. To anyone interested, punch in "FX3" in the search function in the "Racing" and C4 Tech forums, (or "All Forums") and you should come up with many, many threads.

 

Yes, I am confused now. My car has both Z51 and FX-3 options marked inside the center console. I guess Z51 for this car is identical to base with FX-3 with the exception of brakes, bushings and maybe a different ratio steering or a few other things like the little oil cooler/heater? It's strange that even the spring rates are the same, but I guess GM is a strange animal too. Maybe the spring rates were changed on this car. It also has 13" rotors and I don't think those came with Z51 in 1990. I didn't have any luck with the searches, but I'll keep trying.

 

Your car should also have J55 brakes. (HD/ "ZR1" 13" brakes) Your springs are base '90 springs unless changed by a previous owner.

 

The FX3's are speed sensitive so the same setting at 30mph is not the same at 80mph, this from people I autocross with. Then run them full stiff, but since they don't get out of first gear, it really doesn't do anything!

Bilstien will custom valve them if you send them back for a rebuild, don't know if that will alleviate the problem.

BTW here's the infamous C4 suspension chart.
http://www.zr1.net/ZR1_suspension.html

 

Brian, while your statement is basically correct, it confuses the issue. If he follows the recommendation regarding the PROMs that I developed with Bilstein, or uses even one of their standard road race chips, it will eliminate that map and *optimize* the revised valving.

 

Didn't quite ketch the "reprogramming", I was refering to the stock setup.
Which sounds like what he is experiencing.

Is that reprogramming legal in SS?

If so I might be sending a few local competitors your way! :D




[Modified by BrianCunningham, 12:17 PM 8/14/2001]