The Inside Story of C4's Shock Absorber Revolution, Selective Ride Control

[Rob]

New tech article released here at the Corvette Action Center by Hib Halverson:

Corvette Action Center | Tech | C4 Corvette's Selective Ride Control - Six Steps for a King's Ride

 

[tonylong]

Very interesting. Thanks for posting.

 

[So Bay Vetter]

Question for Hib.

My '96 has FX3 but the shock actuators are located differently (so, I assume the shock is different as well). Any ideas on what happend to this system in "96 and why?

 

[Rob]

My '96 has FX3 but the shock actuators are located differently (so, I assume the shock is different as well). Any ideas on what happend to this system in "96 and why?

In 1996, you didn't have the FX3 system, but rather the F45 system which was known as Selective Ride Real Time Dampening. The RTD system is different than the FX3.

 

[B17Crew]

Interesting read, thanks for the story!

B17Crew

 

[So Bay Vetter]

In 1996, you didn't have the FX3 system, but rather the F45 system which was known as Selective Ride Real Time Dampening. The RTD system is different than the FX3.

You're right! I was mistaken . . .thanks

 

[Ugolino]

Wow, what a well-written article. That was pretty sophisticated technology for an option offered twenty years ago. I never really understood what FX3 actually did until I read this article and saw the diagrams, maybe more people would have ordered the option if they understood it. Years ago I had FX3 on my 1990 convertible and the car was quite "floaty" in tour, it was a real pleasure to drive on long trips, but you could definitely tell the difference when you switched it to "perf" on a winding mountain road, the car was so flat on the curves it was like being on a roller coaster. I now have F55 on my 2008 coupe and it's quite soft in "tour", but in city driving "sport" bounces you around like a bag of potatoes (I guess this must be what Z51 feels like).

 

[Toms007]

I would agree as well, it was a very well written, informative article. I have one of the 3900 odd Z07s that were built between 91 and 95. Unlike Ugolinos experience, even in touring mode the Z07 is very firm. I really didn't think that the system was working when I first got it, but upon driving down I70 at speed and switching between settings I could, darn sure, tell the difference. With the Z07 package I find that I can leave it in "Tour" most of the time, and still have the ride and handling I want. However when I took the trip down the "Dragon" I had it set to "Perf" and she was very firm, no body roll or dipping. That's where the Corvette really shined.

Good job Hib!

 

[LT4man]

My '96 has FX3 but the shock actuators are located differently (so, I assume the shock is different as well). Any ideas on what happend to this system in "96 and why?

Dave Hill became the third Chief Engineer of Corvette on November 18, 1992. Dave came to Corvette from Cadillac and brought with him the Cadillac Real Time Damping System. He first installed this on the 96 Vettes. This system separated out each shock individually from the others. Very sophisticated. This system was capable of changing the shock valving at 60 MPH within one foot (12") of travel. Within 10-15 milliseconds for those keeping score. The FX3 system changed the valving on ALL the shocks at the same time. Not so with F45.

They continued with the system on the 1997 C5 and for the next several years. Then Corvette came out with the Magnetic Ride Control system.

The issue with the F45 system is lack of parts and to this point in time, no one rebuilds any of the parts (actuators or shock absorbers). Mine is probably not working as well as when my Vette was new.

Some folks with F45 install regular shocks and disable the electronic part of the system to prevent DTC lights from being illuminated. They report very good results!

SAVE THE

 

[Hib Halverson]

My '96 has FX3 but the shock actuators are located differently (so, I assume the shock is different as well). Any ideas on what happend to this system in "96 and why?

Your 96 does not have FX3.

What you have is F45 "Real Time Damping", an inferior system which has nothing in common with FX3.

F45 is a marketing ploy which was developed in-house by Delco (which was soon-after spun off as "Delphi). It was a bi-state ride enhancement only which had no performance advantages. What's really sad is it was a one-year option so parts support is close to "zero" and the shocks are not rebuildable...or, at least, no one is rebuilding them at this point.

I disagree with "LT4Man" on the idea that the F45 for MY96 was "very sophisticated". In fact, it was quite crude...even when compared to the 97-02 version of F45. It was a bi-state, rather than a continuously-variable system, and thus had very limited band width, ie: damping was either really soft or soft.

 

[LT4man]

I disagree with "LT4Man" on the idea that the F45 for MY96 was "very sophisticated". In fact, it was quite crude...even when compared to the 97-02 version of F45. It was a bi-state, rather than a continuously-variable system, and thus had very limited band width, ie: damping was either really soft or soft.

Hib, maybe this was true on the 96 F45 equipped Vettes you have driven. I can only speak from personal experience. My own Vette and the Vettes I worked on which had the F45 option.

A very easy way to tell how effective this option was, was to find a road with a lot of undulations and imperfections. Living in Chicago, this was very easy for me to do. :L

I would drive on this road with the setting on Tour and pay very close attention to the middle bulge of my hood. The hood would stay almost perfectly straight while hitting all the bumps. I would then move the knob to Sport. One could actually see the hood move up and down a little. On the Performance setting, the hood would physically move up and down with the suspension.

Of course, on a very even road (an Interstate for example) the Performance setting was a hoot for me to use. There was a distinct difference between the soft (Tour) setting and the hard (Performance) setting.

Until just the last couple of years, this system was working very well. I have noticed a deterioration of the ride over the last two years. I am trying to decide what repairs I would like to make.

As I said earlier, the F45 system was based on the continuously-variable system which was designed and developed by Cadillac. Your reference to Delphi seems to be more an "old wives' tale".

Corvette knew they were going to install this system on the "All new" C5. Along with the new water borne paint system, Corvette wanted to make sure these changes were working up to par.

My information came directly from Corvette engineers I spoke with during the middle '90s.

DON'T WORRY, JUST SAVE THE !

 

[Hot Rod]

Hi Hib. Great article, really enjoyed it and learned a lot!

Any chance that you can get any numbers/figures/graphs on the regular shocks std/Z07/Z51 compared to FX3 shocks? Bilstein must have that info.

What I would like to see is how stiff FX3 is fully closed compared to std/Z07/Z51 or how "loose" they are fully open compared to the same.

That would be nice in an updated article!

All the best from Hot Rod in Sunny Sweden.

 

[rockycatt]

i have ordered a replacement gear for the top of the bilstein front passenger fx3 shock
can it be simply replaced ,without rebuilding the whole shock [my vette is 1991 roadster ]

 

[tcxd40]

Well, I will concur an excellent article! My ride is optioned with the Z07 pacakge as well, wish I could use it. The original owner raced this car from day one, pulled the factory shocks out, diasabled the ride control and used Koni fully adjustable racing shocks.
On the good side I have been in contact with Bilstien they will rebuild my shocks and warranty them for around $145.00 each. The original owner did keep everthing he removed and saved it all and not just the shocks either.

tcxd40

 

[Hib Halverson]

I know this is an old thread, but there is so much inaccurate information here, I need to comment on a post made back in January. I'm sorry "LT4Man" but you've got no idea how much incorrect information the old post, above, contains. You may believe a lot of that stuff but some of it is just flat wrong.

Hib, maybe this was true on the 96 F45 equipped Vettes you have driven. I can only speak from personal experience. My own Vette and the Vettes I worked on which had the F45 option.

I've driven several and understand the system quite well.
I'm confident of my facts.

(snip)
As I said earlier, the F45 system was based on the continuously-variable system which was designed and developed by Cadillac. Your reference to Delphi seems to be more an "old wives' tale".

Dude...I freakin' do not publish or post "old wives tales."

Here's the 411 on this sitch...

Delphi was the ride control products designer, developer and manufacturer for GM back then. Cadillac was a marketing group. As for the engineers who developed Cadillacs, they worked for GM engineering on Cadillacs, Buicks and even GMC trucks. Delphi designed, developed and made all the "RTD-type" ride control products (the shocks, the electronics hardware and software) used by Cadillac, GMC Truck, Chevrolet SUVs and Corvettes.

What the various vehicle development groups did is take that hardware, integrate it with the vehicle platforms and do the calibration work, which, of course, was platform-specific, ie: a ride control calibration for a Cadillac DeVille obviously wouldn't work for a Corvette Coupe.

Corvette knew they were going to install this system on the "All new" C5.

That's inaccurate.
Neither MY96 F45, MY97-03 F45 or 04-10 F55 were ever standard equipment, ie: installed on "all" C5s or C6s. Those ride control systems were always an option and, thus, was never installed on "all" Corvettes. I'll add that, with respect to Corvette, there never was any thought to making F45 or F55 standard equipment.

Why?

Cost.

The statement above about F45 being based on the Cadillac continuously-variable systems is partially inaccurate. In fact, the development that resulted in F45 for MY96 occurred before the Cadillac CV system was completed. What was "based" on a Cadillac system is the CV RTD which was introduced for MY97 on C5 and for MY96 in selected Cadillac products. Now, it may have been that the 1996 Corvette RTD was based on some previous bi-state system used in the mid-90s on some Cadillac products. I suggest that's possible because, the time that work may have been going on at Cadillac may have been the same time that Hill was still the Chief Engineer for the Allante. I'm not an Allante expert but I recall that some Alantes had some sort of variable ride control system as an option or maybe as std. equip.

My information came directly from Corvette engineers I spoke with during the middle '90s.

You say you talked to "Corvette Engineers"
Ok.
Who were they?

My information came directly from interviews I conducted with: 1) Scott Allman who was the Lead Engineer for Corvette Ride and Handing between 1988 and late 1994, a period which included the time MY96 F45 was developed, 2) Mike Neal who took over Allman's job and had it until 2005 and 3) Mike Rizzo who was the Technical Integration Engineer for Corvette Chassis Controls in the mid 00s. Those guys were the people who actually ran Corvette ride control development of both F45 for 96, F45 for MY97-03 and F55 for MY04 In addition to those three guys, my statements are based on several interviews (both on 96 RTD, 97-04 RTD and 04 F55) with Darin Dellinger who, back then, worked for Delphi and worked in the group that developed the shocks which were used in the two F45 versions and in the F55 system introduced for MY04. He was the point man for Delphi's relationship with the Corvette engineers.

Now...which Corvette engineers did you say you spoke to about Corvette Ride Controls?

Finally, let me restate the facts about F45 in 1996
1) It was a bi-state (ie: two discrite levels of damping...soft and really soft) system with very limited bandwidth in damping.
2) It was a ride enhancement only and not a performance enhancment. Just the fact that Z51 did not includeit and all 96 RTD cars had incredibly soft springs further supports the ride-enhacement-only idea.
3) It was a one year system and parts support going forward, if it hasn't ended already, is going to become impossible.

At this point in time, I'll suggest that the existence of F45 in MY96 was more GM internal politics and a wet-dream of various GM marketing groups than it was a useful feature for customers. At the same time F45 for MY96 was being developed over at Delphi and advocated by Hill who was, of course, partial to Cadillac, Bilstein and the Ride and Handling engineers at Corvette Development were working on a "high-speed" "third-generation" version of the existing Selective Ride (FX3). It would have used more powerful actuators on the shocks which could move the bypass valves in the shock much faster. It also would have used the same type of "ride sensors" the Delphi RTD system was going to use and, because it would have become ride-movement dependent rather than speed-dependent, would have resulted in nearly the same ride enhancement as 96 F45, but also, because the SRC shocks had so much more bandwidth of available damping, it would have resulted in some significant performance gains, too.

In the end "high-speed" SRC (which also may have been known internally as "fast shocks") was killed and the pet project (the bi-state RTD) of Dave Hill and bunch of moronic GM marketing weenies, which used shocks made by Delphi (which, back then was still owned by GM), got the nod for production.

That was a big mistake which did not serve Corvette customers (or the car's performance) very well.

 

[rockycatt]

i have ordered a replacement gear for the top of the bilstein front passenger fx3 shock
can it be simply replaced ,without rebuilding the whole shock [my vette is 1991 roadster ]

well does any one know if the shock gear is a simple in place replacement or does the shok have to be benched to replace the top gear on the fx3 shock
ty vm rockycatt

 

[aboatguy]

well does any one know if the shock gear is a simple in place replacement or does the shok have to be benched to replace the top gear on the fx3 shock
ty vm rockycatt

Besides rebuilding the actuators they sell the gears and should be able to help you out.
Diagnosis

 

[rockycatt]

thanks for replying ive ordered the gear and paid for it it should be in m y hand in a day or two 8+)

 

[Hib Halverson]

well does any one know if the shock gear is a simple in place replacement or does the shok have to be benched to replace the top gear on the fx3 shock
ty vm rockycatt

If you are talking about the gear on the end of the bypass valve shaft, that gear cannot be repaired in the field by a DIY. If that gear is broken, either the shock need to be returned to Bilstein for overhaul or the shock needs to be replaced.

If you are talking about the splined ring or "gear" inside the shock actuator, I've heard of people repairing that gear but I'm unaware of a source for just the gear. Complete replacement actuators are available from Bilstein and a few other sources.

 

[rockycatt]

If you are talking about the gear on the end of the bypass valve shaft, that gear cannot be repaired in the field by a DIY. If that gear is broken, either the shock need to be returned to Bilstein for overhaul or the shock needs to be replaced.

If you are talking about the splined ring or "gear" inside the shock actuator, I've heard of people repairing that gear but I'm unaware of a source for just the gear. Complete replacement actuators are available from Bilstein and a few other sources.

here is the picture the one on the left there offered by captian z