Need Info On These Shocks

[Tom Duncan]

Hi folks, I need to get some info on this set of shox, one of each set shown. They came off a Lola 202 VFF but they didn't originally come with the car so that's not relevant.

The one on the left in the photo (all silver) is the shorter of the two sets (from the front) and has no makers name on it but the "Do Not Open" in English and German on the body cap might be a tipoff. This shock appears to be pressurized as the shaft on one will slowly come back out after compression though the other does so quite a bit slower so I suspect some pressure loss in that one. No gurgling when the shaft direction is reversed. The stampings at the base are shown in the photos but I'll list them here:

39279190296 228/102 on both. I suspect the first set of numbers is a combo serial/series/date, the second set perhaps valving?

The one on the right is a SPAX, has an adjustment knob that has 30 clicks and appears to affect both bump and rebound at the same time, gurgles on shaft direction reversal so likely needs to be re-built or at least topped up. Has the following numbers on both:

C145DD2 GE2

I'm considering replacing my remote reservoir Penskes on my PRS Club Ford car with these as I want to get away from pressurized shocks but as the silver set is pressurized I think that would be a lateral move at the front of the car.

Any and all info welcome!

Tom Duncan

[DanW]

Shock on left is Bilstein. The 3 digit numbers are bump/rebound.

[R. Pare]

Black shock is Spax - says so with the logo.

[Tom Duncan]

Sorry about that, my initial text disappeared, now put back in.

As to the 3-digit numbers on the Bilstein, what do they signify?

And do the Spax numbers tell us anything?

Tom

[DanW]

As to the 3-digit numbers on the Bilstein, what do they signify?

Tom

Hello Tom,

The older bilstein dampers were rated in newton-meters at a velocity around .5 m/sec. I can't seen to find the info at the moment.

I know you build your own, but Bilstein can rebuild your shocks for about $100/shock plus parts. They can also sell you replacement parts. They are quite reasonable. I think your best bet on the Bilsteins would be to call them direct, ask for their motorsports engineering group.

I had the shocks for my Zink rebuilt by them. - Dan Wise

https://cart.bilsteinus.com/portals/0/PDF/BILSTEIN_MSCat.pdf

[troyt]

Making the PRS vintage legal?

[Tom Duncan]

Hey Troy,

Yep, vintage seems to be where it's at in regards CF around here. We had 12 CF's at the CSRG Charity Challenge, 43 cars overall in an exclusive FF/CF group and an additional 12 cars were turned away. Haven't seen numbers like that in SF region SCCA in decades.

Tom

[Tom Duncan]

Hey Dan, thanks for the suggestions on the Bilsteins, esp the link to their catalog, lots of interesting stuff in there.

I was initially thinking of trying to find a shock setup that would work for both SCCA/CF/AR133 and vintage VFF tires but now I'm thinking maybe I'll just commit to vintage.

Tom

[Bob Posner]

Hey Dan, thanks for the suggestions on the Bilsteins, esp the link to their catalog, lots of interesting stuff in there.

I was initially thinking of trying to find a shock setup that would work for both SCCA/CF/AR133 and vintage VFF tires but now I'm thinking maybe I'll just commit to vintage.

Tom

Several Crossle and Titan cars here use the steel bodied Koni shocks with AR and Hoosier VFF tires without any setup changes other than front ride height to account for the smaller AR Handling is equal accounting for slightly less grip on Hoosiers.

[DanW]

Hey Dan, thanks for the suggestions on the Bilsteins, esp the link to their catalog, lots of interesting stuff in there.

I was initially thinking of trying to find a shock setup that would work for both SCCA/CF/AR133 and vintage VFF tires but now I'm thinking maybe I'll just commit to vintage.

Tom

Hello Tom,

I keep the Penske's with their springs and ride heights set for the SCCA/AR tires. I have similar adjustable spax for vintage. I change them back and forth as needed.

Dan

[Tom Duncan]

Hey Dan, I was thinking about doing what you are doing, two sets of shocks/springs, especially if I can find some vintage-proper cheap enough with the right lengths and valving. I already have some Hyperco springs in the projected rates.

On the other hand if commit to vintage I can sell my 8100s and get some maybe nicer shocks like Konis and use them primarily for vintage but of course they will work fine for SCCA. My car originally came to me with steel body double adjustable Konis and they worked fine but they would wear out 3/4 of the way through a season and I had to pay Koni something like $700 to rebuild them each year, probably more now. I figured I could get Penskes, rebuld them myself when needed and they would pay for themselves after a few years. One thing I don't like about the Konis is you can't rebuild them yourself.

Tom

[Tom Duncan]

A bit off topic but one shock I was considering is the QA1 Proma Star. I talked with a dealer for them and they looked promising until I found out the shock cannot be used as a droop limiter due to the thin body wall and just a few fine threads holding the cap on. While likely not a problem for 'normal' race use one whack of a curb that gets the inside tires airborne resulting in rapid full extention of the shaft/piston could easily decaptiate the shock body...not so fun.

However it ocurred to me one could put three screws through the top of the body and into the cap that would take the brunt of such an occurance. I mean to get back to the guy I spoke with about this and also look into the attachment of the lower body to the shock eye/base.

Tom

[Hardingfv32]

...one whack of a curb that gets the inside tires airborne resulting in rapid full extension of the shaft/piston could easily decapitate the shock body...

Is this a valid concern? Regardless how rapid the compression event is… would not the rebound be controlled by the spring rate and shock valving? The spring force at full extension would be the lowest you ever see. The shock in going to provide a dampened rebound motion.

Am I getting something wrong with this logic?

Brian

[Tom Duncan]

Thats a good point Brian, the rate of drop against the cap wouldn't be free fall, the rebound control in the shock would slow it down. On the other hand if you saw how thin the walls of the shock body were and how fine and short the threads were you might think it's still a concern.

Tom

[Tom Duncan]

Just spoke with Mike Naake of Naake Suspension Specialists in Roseville CA about the possibly iffy droop limiting capabilities of the QA1 Proma Star aluminum body twin-tube shock.

He felt that with the relatively low overall weight and low unsprung weight there would be no problem with the shock shaft/piston assembly pulling through the cap unless you got airborne with both wheels (front set or rear set) coming off the ground at the same time. Even then as Brian pointed out the rebound resistance would be doing some work to slow the shaft and Mike pointed out if it is just one wheel off the ground the anti-roll bar would also help the airborne shock to ease its way down.

The price on these is quite good, the double adjustable is around $280 and the single adjustable (affects both rebound and bump in a range of 250#) is around $200. If one doesn't change springs much (and then in small increments) the single adjustable would be fine.

It might be possible to get a set of new shocks for less than $1000...not bad against the Koni 8211/8212s which are at least double that, and reportedly often triple or more.

The catalog lists stock lengths as follows (extended and compressed):

11-1/8" x 8-3/4"

12-3/4" x 9-1/2"

14" x 10-1/8"

To accomodate slightly different lengths there are extended eyes available in one half inch increments, though piston travel would need to be closely looked at.

The stock spring perches are for 2.5" ID springs and most CF/VFFs I've seen use 2.25" ID springs. He said he has turned down the perches to 2.25" and I've seen the perches and there is plenty of metal to do that. I've also seen in QA1 factory literature/webpage a reference to them being able to supply 2.25" perches, which I will check on.

Tom

[Fmracerbob]

Tom : Why would you even consider using a miss-matched set of old shocks ? Who knows how the Bilstein is valved and it's not adjustable plus meant to be mounted "upside down" to reduce the unsprung weight. And then try to match that to the Spax, which in my experience never were all that good.

I ran a set of the Bilsteins on my Royal RP-24 but they were specifically valved for the springs used which also were custom wound so there was always some compression at full droop. This is how it is supposed to be done but seldom is as it is easier and cheaper to buy springs in a standard length. When we ran the F3 cars in the 70's all our springs were wound so they had the same static RH at a specified extended length of the shock.

If you really want to be able to run the car with more than one brand of tire then you will need a double adjustable shock and might well have an alternate set of springs for each brand of tire, just like for rain running. Ditch those "modern" shocks and see if you can make a set of the QA1 Proma Star DBL Adj work. I am leery of a shock with a body so thin it could pull the tops out on full droop though. I suppose you could use some form of droop limiter.

I am surprised a set of the Koni's would wear out as fast as you have experienced, especially on a Club Ford. We have run them for years on the range of high end and seriously fast vintage cars out of our shop. Most of those cars put a whole lot more work on them than a CF could and we get at least 20 or more weekends before they show measurable wear. But then we also have the shocks rebuilt and tested at PRS right here at the race track rather than send them out.

Looking forward to seeing you out there next year.

Bob McCormack

[Tom Duncan]

Well Bob the main reason I initially put up the thread was to see if the codes on the side of the shocks gave me the valving. I certainly wouldn't just put them on the car and race with them. A friend had hem taken off his car so I asked if I could play with them, perhaps learning something along the way. While my PRS originally came with Koni 8211s I quickly changed to Penske 8100s and have no experience with anything else.

So far no one seems to know if and what the codes might mean in the case of the SPAX and with the Bilstein the rates are there but no seems to know how to interpret them. In addition if the valving was reasonably close I would then dyno them to confirm, and only then consider putting them on the car.

I'm thinking I really want a twin tube shock to reduce internal gas pressure to a minimum to enhance tire to road compliance so the QA1's are looking better and better. Plus I think the single adjustables would be fine as I don't plan on changing springs much if at all.

I'm curious about your mention of 'custom wound' springs to make sure there is no dangle at full extension. I've been using helper springs of about 100# in conjuction with the regular spring at the back of the car and that has been successful in eliminating dangle and keeping the inside tire positively on the road if I don't have the rebound too high. I've never heard of custom springs...is anyone still offering that? I could use a set for the front of my car as I've got a bit of spring dangle up there.

I'll inquire as to the actual shock body wall thickness of the QA1s. I didn't measure it when I was inspecting the shocks at the Naake shop but they looked pretty thin, especially at the threads. On the other hand the Proma Stars are used by the circle track guys so they must hold up, though they don't use the shock as a droop limiter.

I was also surprised by my original Koni's dying about 2/3 of the way through a season of regional racing. Basically they became softer and softer and responded less and less to adjustments. I'd send them back to a Koni service center (I think it was Truesports) every season, they would say the shocks were pretty nackered and $700 later they'd be back on the car. I suspect the car bouncing around on the trailer 13 times a year didn't help. At the time Sears Point was very bumpy so that also may have contributed.

Tom

[Fmracerbob]

Tom

As to transporting. I learned long ago rule number one is to always strap the car down by the chassis, not just because it avoids wearing the suspension components but also will stay put. Running straps around tires or outer suspension points has too many variables including changing tire pressure. Folks just don't appreciate all the wear the shocks get. If one must tie down by the wheels, say because the trailer is unsprung, then set the shocks to full soft while transporting.

I have to admit I never heard of shocks designed for racing/hi-performance coil over that were at risk of the tops stripping the threads out of the body. I would think that is one of the basic loads a designer calculates. And as others have mentioned, the rebound valving along with any internal damper, there should be one for full extension, would handle the loads rate of occurrence. A CF has pretty low unsprung weight.

As to the QA1's, the single adjustable apparently has a designed in relationship between bump and rebound so changing one comes with changing the other. That was how the old Armstrongs we used to have to run in the 60's and early 70's were and it never really worked that well. When independent adjustments became available in other brands it make a very noticeable improvement in adjusting the handling. In these days, from my perspective, shocks are the most important adjustment in the arsenal of tools to make a car really work, especially a light weight car.

As to the springs, I learned from Carrol Smith back in the late 60's the best way to work with changing spring rates was to establish the basic ride height for the vehicle. Then we would come up with the shock length for each corner at that RH. Once we had a base line spring rate to support the car at that shock length we worked back from there. Spring makers can design a spring to have a specific rate at a given compressed length. Then the rate for each inch of compression can be designed in for each different set of springs. They will all have a different free length and maximum compression. What changes is the dia of the material and number of coils. Granted this is more expensive than just buying off the shelf springs with different compression rates. For most racers, having quickly changeable rates that don't upset the basic setup is way too expensive. Running professionally is a different story.

However in the case of my Royal, once we knew what worked it was just a matter of having one set of springs custom wound. The "helper springs" do a good job of keeping the spring from rattling at extension but there is an abrupt rate change once the they fully compress and the main springs becomes active. The ideal is to have the main spring never become unloaded during the normal course of running, with the helpers only really needed when the car is jacked up off the suspension. That usually means the longest free spring length for the compression rate. Movement sensors and a computer really help in this determination.

I'st worth keeping in mind that the unsprung and sprung weight front and rear are different as well as the motion ratios so it would be unlikely the same valving would work for both ends of the car. I always end up having the valving modified to suit the final forces at each end once spring rates and shock settings have been settled upon. That way I have adjustment in both directions as time goes on, things can change over time and even from day to day depending on track conditions and tire wear.

And don't think a spec class with specified spring rates gets around all this, bump rubbers and packers are another whole world to play with.

Bob

[Tom Duncan]

Thanks for the info Bob, very informative. As to having custom wound springs I would have to count myself in with those that would consider that to likely be too expensive, though I would be interested to know who offers that service and at what cost.

Tom

[Dave Harmison]

T

[J Leonard]

Thanks for the info Bob, very informative. As to having custom wound springs I would have to count myself in with those that would consider that to likely be too expensive, though I would be interested to know who offers that service and at what cost.

Tom

Renton coil spring

[Dave Harmison]

To clarify, as I think was already said, the numbers on the Bilsteins are in decaNewtons at .52 m/sec per page eleven of my Bilstein manual. So, if it is stamped 275/78 that is 2750 Nts at 0.52 m/sec in rebound and 780 Nts at 0.52 m/sec in compression. And they are linear, like all caps linear. To draw the shock curve, start at 0,0 on the graph paper and draw a straight line through 2,750 at 0.52 and you have your rebound curve, likewise the compression.
Is I recall from the last time I spoke to Bilstein, they didn't service the small rod shocks anymore, the new shocks have a 14mm rod and yours are, I think, 10mm.
If you want a project, your shocks can be changed over but I doubt it is something Bilstein would be interested in.
I have brazed valve stems on my old Bilsteins so I can rebuild mine, but that's a whole
project in itself.
Without getting into a debate about the pros and cons of linear damping, I'll just say there are pros and cons.

[DanW]

T

Dave,

You are correct on the number values on the bilsteins. I had my old Bilsteins rebuilt by Bilstein and they used the 14mm rods. I used the values that Steve Lathrop provided for my Zink Z10. Yes, they are linear but they are a good shock and work well for their purpose, particularly since the older cars' motion ratios are so low.

Tom Duncan,

There are domestic sources for custom wound springs to your specs. I think you will find the costs competitive with Hyperco and others. I used to have custom wound springs made locally when I worked in the refinery when the equipment OEM no longer existed. Now its almost all cad/cam design and wound to order.

Regards,
Dan

[Hawke]

I'm the Australian Agent for AVO shock absorbers and I've supplied shocks to replace Bilsteins. The AVO is a twin tube with a single adjuster, very similar in appearance to the Spax above.

Once you know how to interpret the numbers on the Bilstein, you can alter the AVO piston and or shims to match those figures of bump/rebound. The curve wont be linear, but more regressive, with a marked knee just before 2" per second. This seems to suit many people.

I normally set the adjuster to the mid range, so that damping is similar to the Bilstein, and if wet, they can be wound down to full soft, or, you can go fully hard to rattle your teeth.

If the shock is too long for the application, I find that a spacer under the top gland works, or if warranted, a shorter shaft will work. I've never seen a top retainer come off.

While this is what happens in Australia, I'm sure that someone in the US can do similar things to other twin tube shocks.