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Fanns en artikel om FX3 på Corvette Actioncenter men nu är den borta? Jag har den i min dator så jag postar den här, ett långt inlägg...
1989 - 1995: Technical Article: FX3 Selective Ride Control
FX3 Selective Ride Control Shock Absorbers - Part I
A look at the RPO FX3 Selective Ride Control system on 89-95 Corvettes. The "SRC" article is by Hib Halverson, a technical writer and CAC member who, at one time or another in the last 20-years, has worked for every Corvette magazine that is distributed nationally, including Corvette Quarterly, Vette and Corvette Fever. He is best-known in the Corvette community for the "Big-Block from Hell" and "Purple Project" series he's written for Vette Magazine.
Copyright June 3, 2000 Hib Halverson
Hi Vettenetters and Zroners- Some subscribers to these lists are aware that Bilstein Corporation of America offers a repair and revalving service for many of their shock absorber products including the ride-adaptive, Delco-Bilstein shocks used on 89-95s equipped with RPO FX3 Selective Ride Control (SRC).
For a period of time in 1998 and 1999, if you sent SRC shocks into Bilstein for revalving or repair and they found them leaking, the shocks sometimes could not be repaired and had to be replaced. This was caused by a long-standing, back-order of the SRC shock absorber piston rod assembly at Krupp-Bilstein in Germany, the only source for that part. The piston rod back order was finally filled earlier this spring and Bilstein North America now has them in stock.
This piston rod assembly is actually two shafts, one inside the other and is manufactured as a single unit by Bilstein in Germany. The outer shaft doubles as both the piston rod and the outer section of a sleeve valve that controls the flow of oil bypassed around the shock's main valve. The inner shaft is the other part of the valve. As the inner shaft rotates, the bypass valve opening varies. The top of the inner shaft is splined and engages the SRC electric actuators which, in turn, are operated by the SRC controller. To vary the bypass valve opening, the SRC actuator turns the inner shaft. The larger the bypass valve opening, the softer the shock valving and the smaller the opening, the more aggressive the shock valving.
There is a potential wear problem with this piston rod assembly. If the seal between the two shafts fails, the shock will begin to leak oil. If the actuator is attached, the leakage will appear to come from beneath the actuator. When the seal fails, the oil is forced up, through the space between the two shafts, and out the top of the shock through the small gap between the splined end of the inner shaft and the shoulder of the outer shaft. Any oil leakage out the top of the shock or, if the actuator is in place, from under the actuator is indicative of piston rod inner shaft seal failure. This type of leakage is not to be confused with the slight oil film the Service Manual says is permissible on the piston rod or on the sides of the shock absorber itself.
Cars with over 30,000 miles that have had frequent changes of the SRC selector switch and/or have had many ignition cycles will be most susceptible to shock leakage due to this seal failure. Whether or not the seal fails seems to be affected by how much valve movement there has been during the life of the shock. Every time an FX3 car is started, the SRC actuators index themselves by moving through their full travel then returning to the valve adjustment called for by the selector switch setting and vehicle speed. The more often the inner shaft is moved, the more likely there will be a problem with leakage.
The front shocks can be inspected for leakage when they are in place. If leakage has existed for some time, shock oil will be present inside the actuator retaining bracket at the very top of the shock, on upper shock mounts and, maybe, on the frame's upper, shock mounting bracket. The rear shocks must be removed for leakage inspection. Rear shock removal requires the rear actuators be separated from the shocks after they are unbolted but before separating them from the car. Any oil leakage from the top of the shock will be obvious once the shock is removed.
If you have SRC shocks that are leaking oil in the manner discussed above, they can be repaired. Bilstein has the parts in stock and the charge for repair is minimal compared to the price of new SRC shocks.
If you are an aggressive street driver, autocrosser or road racer, you can significantly improve the handling of your FX3/SRC equipped car by having Bilstein revalve your shocks. Several valving configurations are available including one that works well for 89-95s that are dual-purpose, street/track cars. The valving for all six-ranges is stiffened up with the low ranges changing only slightly, but the upper ranges becoming significantly stiffer. Additionally, the rear shocks get a substantial increase in rebound valving which helps the 92-95 ZR-1's tendency towards drop-throttle oversteer. This problem is caused by a combination of: high lateral acceleration, sudden forward weight transfer, 200 lbs more on the front end, soft spring rates and soft shocks. The approximately 50% more rebound valving Bilstein dials-in, resists the weight transfer and makes the car less susceptible to drop-throttle, oversteer.
My 95 had problems with leakage from the front shocks. I removed all four and sent them to Bilstein. Sure enough, the word came back that both the front shocks were low on oil and one of the fronts was almost dry. Since my shocks were there for repair, I had Bilstein revalve them, too, and I picked the street/track valving configuration.
The effect revalving the shocks had on my car's handling was outstanding. In the lower SRC ranges, the wheels seem better damped. The floating effect of the OE valving's soft rebound control is gone. I occasionally autocross my 95 and the upper SRC ranges are noticeably stiffer offering better control during aggressive maneuvering.
I recommend the Bilstein revalving of SRC shocks to anyone who drives an FX3-equipped car aggressively. The revalving is especially useful for 92-95 ZR-1s and 92-95 Z07s. For more information, contact Bill Hindorf at Bilstein North America, ph: 800-537-1085 . You also can write Bilstein at 8845 Rehco Rd., San Diego, CA 92121.
FX3 Selective Ride Control Shock Absorbers - Rear Suspension Bushings - Part II
Below, is a followup by Hib to Part I above...
Copyright June 8, 2000 Hib Halverson
Vettenetters, Zroners- Last week I started a thread on SRC.
I was amazed by the response and how widely that post has been circulated. Because of that, I'd like to expand on my original comments a bit.
First of all, my recommendations were specific to the 1992-95 iteration of SRC. The 1989-91 version is somewhat different, both in the shocks--they have no valving on the bypass circuit and I believe a larger (in degrees) valve movement--and the system may use a different controller. The revalving I discussed on my post of last week works well for 92-95 shocks used in street/track driving.
I have no experience with revalving the early shocks and anecdotal feedback regarding Bilstein revalved, 89-91 SRC shocks used with the OE controller seems a bit mixed. I need to develop additional information about this issue before I can discuss the early SRC shocks adequately.
Secondly, I got some questions about SRC shocks from a ride standpoint. Make no mistake, the Bilstein revalve of the SRC shocks does not enhance the car's ride. It's mainly a performance handling modification. If you do not regularly drive your FX3-equipped C4 in an aggressive manner on the street or you do not autocross/road race the car, you may not care for the rmore aggressive ride you get with the revised valving. If your FX3 car is driven in a normal manner on the street and a nice ride is an important consideration, don't have the shocks revalved. Now, if the shocks are leaking (as discussed previously in this thread) or are otherwise worn, Bilstein can rebuild the shocks and, usually, that will be less expensive then buying new ones. When you send the shocks in for rebuilding, just don't opt for the revalving.
Other rear suspension comments:
Yesterday I called Doug Rippie to discuss a new product development project Fluidyne High-Performance (the radiator people) have given me. In the process of discussing that, Doug commented about some past statements I've made on VN, ZR1N and Corvette Forum about the use of polyurethane suspension bushings in the rear arms of C4s.
Initially Doug disagreed with my contention that use of urethane in C4 rear control arms (both trailing and lateral) may actually degrade suspension action because they are so stiff that they can bind the suspension. To review, the C4 rear suspension geometry is such that, as the trailing and lateral arms move, they *also* rotate. Very stiff control arm bushings can resist or restrict this needed rotation. If that happens, as the suspension moves, it can partially bind. When the binding occurs, the effective wheel rate goes up making the suspension action non-linear. That can make the car twitchy and unpredictable.
Rippie pointed out that in the heyday of C4 Showroom Stock and production-based road racing in the mid-late-80s and early 90s, racers had success with use of urethane in the rear of C4s. I pointed out to Doug that some of these race cars had limited suspension travel and high roll stiffness such that the suspension might not move enough such that the binding would be a problem. I also pointed out that on many street driven cars and even those that are raced with stock suspension travel and roll stiffness levels, may see problems with binding, when the stock rubber bushings are replaced with urethane parts.
In the end Doug and I agreed that in situations where the rear suspension is basically stock, the use of polyurethane in the rear arms may degrade handling because of the binding problem, however, we also agreed that in race-only applications or street/track cars having rear suspension highly modified, ie: higher rate springs, bigger bars and lowered ride height/limited travel, the use of urethane might not be a problem and could be an advantage.
For borderline cases, if you want to use poly bushings, try them but do a lot of testing. If the car is twitchy or unpredictable in transient maneuvers and you can't find anything else wrong, take the urethane out and test again.
All that said, for race cars, the best way to go with an all-out racing C4 rear suspension is heim joints.
.. vips var bilen 25mm högre.