Bilstein Dampeners
 

I've been running the bilstein dampers from ISC racing for 1.5 seasons now. I experienced a failure yesturday.

Any of you guys having problems with yours? Also as I'm trying to find a replacement I learned teh following about the rear dampener that ISC racing uses:

The rear ones are from a 1971 BMW 2.8L Bavaria...

Lastly did you guys know Bilstein now makes a direct replacement shock for the 2nd gen rx7s?

He-he. I am running BMW e-30 rear Bilsteins on the back of my Ford Focus. Bilsteins are my favorite off-the-shelf damper (it isn't a dampener). Their application coverage isn't great, but it is easy to find something that works. Plus, rebuild and revalve is only $65, compared to double that for Koni.

I have never seen one fail like that. I imagine if you call their office in San Diego tell them what happened, email them a picture, you should be good to go. Be warned, their warranty is void if you put the shock on something other than what the catalog calls for.

I use the Bilsteins from Mike at ISC racing on all 4 corners of a 1st gen RX-7 road race car & would be mighty pi$$ed if I was sent shocks with FAULTY WELDING. I would suggest to start by talking to Mike & if he says tough $hit send a picture & tell Bilstein you were using them on a 1971 BMW 2.8L Bavaria. If the friken valving wore out that is one thing but the friken weld breaking is quite another thing. & by looking at the picture it is not the parent material that broke.

It failed just as was exiting a corner I just made through. I think it was something like 5500 in 3rd gear when I heard a bang and the rear end snapped around to one side. So I jerked the wheel to counter steer and took my foot off the gas and coasted wondering WTF happened. Good thing i was only 1 corner away from Pit entrance and pitted. I thought I blew the tire and it wasn't teh case... Scared teh hell out of me... Good thing it wasn't during the max lateral accerlation portion through the corner at 5000 in 3rd...

I would say you shouldn't put a solid hunk of delrin in a shock end that has to pivot a couple degrees. It doesn't look like a manufacturer problem to me unless that bushing is some kind of hi-tech delrin spherical bearing.

???

Mike at ISC racing supplied the delrin bushing. It came preassembled with perches, springs, and the dampener with a delrin mount. I just bolted it to my car and corner weighted everything... I ordered his front and rear suspension setup. He said it was quick and low maintance since there are no settings or anything to fiddle around with. That was my selling point. The competing setup was ground control with Koni Yellows...

I do agree that teh delrin mount should not be there, as it does not allow any deflection for an item that needs to be self alignining. I can also tell you teh ID hole of the delrin bushing has been oblongated by eye ever so slightly. I didn't give it a second though and just bolted it all up thinking I bought an off the shelf proven race suspension.

That wear is probably from the bushing binding. Mike is a nice guy and a fast driver but I thought he had gotten better about little details like this. I pulled a car apart a number of years ago that was built by ISC. The front camber plates were just that,plates. A piece of 1/4" steel with slots cut in them and a hole for the strut shaft. The explanation the owner got was, "There isn't enough change in angle to worry about".
As you have found out any change in angle will eventually cause problems. Its either going to break or bind. Since it was binding you had added an unknown to the rear suspension. When was it binding? If it was when the suspension was compressing it sure wasn't helping you come out of the corners hard. The shock body or more likely the shaft was becoming a spring in suspension equation.

I'd get a new shock and either get some spherical bearings put in the ends or go with urethane.

My suspicion is that your problem stems from the delrin inserts. They are probably not allowing enough misalignment between the top mount and the bottom, placing stress at the next weakest point. Apparently, that is the weld.

Really, you should be using a bearing in the bottom mount. Rubber has too much give, which I imagine you already know, but you must remember that as the suspension articulates, the top and bottom mounts don't stay lined up. I think the delrin doesn't have enough misalignment.

EDIT - I took a break to make some Lego with the kids in the middle of posting this and it looks like it has all been covered.

I guess now I'm having to visit the machine shop at work and turn some urathane or something. Problem is the ID of the shock where it accepts the bushing is 40 mm in diameter. With a 20 mm ID. Not a very easy to find sphereical bearing. I've looked at mcmaster carr and through my SKF/NSK catalog at work and didn't find anything that fit that. My next approach was surf mcmaster-carr and see what urathane rods they sell. they sell a 40 mm OD rod, but in 39" lengths for 160 bucks. Kinda a lot especially when I really only need like 6 inches. Looks like I'll be buying a 3" rod, 6" long to turn.

Question I guess is if it is better to run a crush sleeve so that bushing can stay clamped between the stud and the huge washer that holds the shock on the trailing arm?

http://www.hrpworld.com/index.cfm?fo...action=product

See if any of those will do the job. If not http://www.fluro.de/FLUROHoehnHome.htm and have HRP order the one you need.

Unless I am misunderstanding what you are saying, I do not like the idea of a washer clamping on the bushing as that means that metal has to flex in order for the bushing to work. Based on previous experience, I think this is something that you would prefer to avoid also.

The 40mm OD bearings I found at HRPWorld.com had an 18mm ID. They were also $45 ouch. Does that shock stud come out of the control arm? If it does I would turn it down to 18mm or totally make a new one that has a much smaller dia. With a smaller dia you could make a sleeve to fill in the shock ID and get a much smaller bearing.
You will need some way of keeping the bearing centered in the shock but that can be done with the sleeve some how.

Can you find any place local that works with urethane and buy a few 'drops' from them? I've bought small pieces of delrin that way. I've also bought urethane bars from plastic supply companies by the foot. They usually have a minimum order of like $40 or so that will get you a couple feet.

I bought some urethane that was 2" OD and had a 1/2" hole in it that was cheaper than a solid bar. When I machined it I shoved a 1/2 bolt inside it for some support and also put it in the freezer for an hour. You can get an OK rough finish without freezing but for the final trim to size you can get a couple minutes of hard material to work with for an accurate cut.

PM me if you go this route I have some more tips and I might even have some urethane laying around you could use, I'll check at my shop tomorrow.

If there is a stud coming out of the control arm, cut it off flush with the arm, drill in the center and tap it 1/2". Then get a shell designed to carry an off-the-shelf 1/2" ID spherical bearing (removable circlips would be nice over heavy press fit), weld the tube to the bottom of your shocks (one of which has conveniently removed the orignal mount for you), pop in a bearing, locktite and bolt down with 1/2" fastener of correct length and drive on. You might have to space it out a little, but 1/2" ID bearing spacers are a dime-a-dozen from circle track places as that is what all the shocks they use run.

You should be able to perform the above without custom machining skills. Clearly, you will want a good, strong weld and have to be careful not to fry your shock, but other than that, this could be pretty easy and the absolute last time you ever have to think about this mount.

The stud is removable.

The stock bushing fits over the cylinderical section which is turned from a stock hex. I think the hex is like 24 mm or seomthing. It is then threaded at the other side of the hex to thread into the trailling arm.

This piece is then drilled and tapped for a M14x?? mm bolt with a 17 mill head. One side of the shock's bushing sits against the hex, The other side then sits against this metal cup washer (see picture).

First however i'm going to call ISC racing and talk with Mike tommorrow morning about this matter, as you guys are off for memorial day I couldn't get a hold of him... Hopefully he has experienced this before and has a solution to this problem. I wonder how many people are running this exact same setup.

V8mongrel, thanks for all the tips, but the last hting I want to do is go borrow a welder from someone and try to make something work. I do know how to weld, and I do know how to machine, but I rather not. I dont' have access to a machine shop anymore having graduated from university. I could draw something up in CAD and send it out and have it made but at what cost? If something else breaks on this suspension package than I know it's a sign that I completely went the wrong route and should've gone with Ground control and their Koni Yellow or KYB AGX setup for almos the similar price. Atleast they CAD plate their stuff so that it doesn't rust in the rain. ISC didn't even put paint on any of the metal. I had to take it all apart after and spray bomb it.

I agree that your best bet is to call ISC and see what they say. The delrin is going to cause problems, so you need to move away from that. While Koni or KYB might seem appealing at this point, chances are you will have just as many if not more problems. Neither of those are going to come with bearing mounts, so you are in the same boat or paying a lot of money. Rebuilds on Konis are more expensive, and in my experience, more frequent.

I am looking at running a circle track shock on my 79. They come with bearings, many of them you can rebuild or revalve yourself, and they are designed for racing rather than just a part that happens to fit and work like you are running now. Struts are much more difficult to find in a universal setup, but for a rear shock, I think you would do well to look at places like Coleman Racing, Speedway Motorsports and others I have listed here.

V8monger, thanks for sharing the links.

I have one for you. If you ever want to buy lexan sheets to make windows or windsheilds (cars/motorcycles), delrin rods. etc....

goto http://www.gepolymershapes.com/
they have all the information about the various plastics that GE makes. Unfortauntely it looks liek they don't have urathane, which is what I'm aiming at with a stainsteel crush sleeve. The ISC racing units didnt' even come with crush sleeves. I had a good look at the stock rear suspension today in the garage. I'm going to replicate that one pretty much.

oh and for branc locations goto
http://www.gepolymershapes.com/pshap...lLocations.jsp

They sell retail. Usually to small and medium buisnesses. So if you just buy one sheet of whatever or cut offs the local store cuts me a big break because they know it's for a hobby and not for making money.
-Jason

Just finished talking with Mike at ISC racing. He is telling me that I'm clamping the bushing and not allowing rotation of the bushing causing the shock to bind and the weld to snap. He is saying that the cup washer should be loose, loose such that you can rotate it when the whole assembly is clamped. Which I find troubling. Because the washer will bottom out on his supplied spacer which fills in the void between the stock stud (since it's too short) and the face of the delrin. In my opinion the clamping pressure by the bolt clamping the spacer and the stud will prevent the cup'd washer from rotating.

He also thinks I installed the cup washer backwards. I'm not 100% certain if I agree. Do you guys remember how the stock setup is? THe FSM does not accurate picture the washer to show how it goes together.



I think I'm going to redo the setup myself. I found a place in mississauga that sells ployurethane rods. I'm giong to buy a 6" rod and turn it down to 40 mm, and make a new crush sleeve. I disagree completely with this race shop.

If the washer you are talking about is the one that has the arrow in your previous picture, were you to reverse it, you would most likely have metal to metal contact so I think that would make it worse. Looks to me like the outer edge of the washer would touch the outer edge of the bushing shell.

Indeed. Which would not allow for any compliance.
See attached picture...

The way I see you need compliance in two directions. Tilting the shock between the diff and the wheel (ie left and right in the pic)...

and

Rotating the shock between the front and rear bumper. And combination of the above at the same time...

FWIW, I am not sure that polyurethane is going to help all that much. Sure it is softer than delrin, but it might not provide enough movement. Sure you can spec a softer durometer poly, but at that point you might as well be running rubber.

Sorry to see the failure. That shock needs a bearing or bushing that will allows it more freedom and I'm certain the weld failure was from binding of the solid bushing. Ideally use a spherical bearing. If you don't want to spend money I'd use a rubber one.

Mike at ISC may be a good guy and build fast cars yadda, yadda, yadda but he is flat wrong in this case.

I'd go with the urethane, try to get some that you can squeeze a little with your fingers. I can't remember what the stuff is that I have, I want to say "75" or "65". I think it will give you enough flex but it will still put a very slight load on the shock. It won't be enough to break anything though and I doubt it will be enough for you to feel. The amount of movement needed is only a couple degrees.

I don't agree with the shop either. Mike is a nice guy and will loan you anything at the track and for some reason he has some fast cars(4 or 5 at any one time, he rents them out)
I guess somethings will work OK for a while being engineered about 80% of the way.

See attached pics.
Summary on how mike has his setup. The mounting stud OD is 20.00 mm exact. It looks like Mike then drilled and reemed the the delrin bushing so that it has an ID of 20 mm. However the stud is too short, so he made a 10 mm width by 20 mm OD with a 14 mm hole drilled in the middle to fill the gap between the surface of the delrin bushing the end of the stud. In my opinion ISC should've used a metal crush sleeve instead the spacer. Anyhow what is done is done. So I installed it anyways. I bought the setup because I thought ISC cars were fast and I wanted a fast simple setup.

I should've went with the KYB AGXs and ground control. They are stock replacement high perf shocks which do not need this new bushing or anything. They just use the mazda designed stuff. IT was the same price pretty much...

Are the AGXs any good? I have never heard anyone say a kind word about them for any car.

A lot of the E-prod 2nd gen guys seem to like them a lot. K2RD used to offer a kit similar to Ground Control with KYB AGXs installed. People have said they are better than koni Yellows.

Then again peolpe say bilsteins are better because they don't fade. Right now You can tell what my opinion of them is (performace is good), but having to re-engineer the damn thing is not what I wanted.

BTW I attached some pics of a stock setup. I had a friend run out to his car and grab some pics with his cell phone. I redrew it to clarify for others...

So when Mike told me that mazda has the cup'd washer tapering towards the differential and not towards the shock is BS. I told him it was the other way around and we a little bit of that there. I told him I reinstalled your (ISC) shocks 20 mins after taking out my.

I am surprised that an off-the-shelf damper can work with the elveated spring rates of race cars. Is this the RX-7 AGX, a special motorsport damper or something that just happens to work, similar to your Bilsteins?

It's an rx7 specific dampener. Meant for street/sport stiff spring rates...
The limit for the dampeners I'm told are:

400 lb-in spring for fronts
300 lb-in spring for rears.

Anymore and the shock won't be able to dampen them on the highest setting.

I run 400 and 250 right now.

As you can see from the above pic of a 17 year old rx7 with stock suspension never touch before, I did install my shocks correctly as per mazda. It is Mike who is wrong... which makes me even more mad.

If you are going to change, I think you might be better off looking for a more dedicated race damper. Obviously, it is all money and I understand that. I am thinking about contacting www.sellisengineering.com for my needs. No affiliation, no experience, etc, etc, but it might be worth calling them and see what they say. If you call them, please post how it goes.

In reality, I'm looking for a budget basement setup that works good, not the best. Hence I chose those bilsteins.

I may try these guys: http://hotbits.ca/

They are down the road from me, canadian, and looks like they are very active in the ontario amatuer motorsports scene.

On the products page, Ellis is advertising a complete coil over shock with valving to your specs for $105.90 (US). That is cheaper than anything else I can think of. Implications of that are of course both good and bad.

I think a couple of Focus guys have run the Hotbits and been quite happy. Would be a good choice especially if they are local to you.

Again I stress that you want a spherical bearing or a softer rubber bushing that will allow the shock to move freely.

If the shock bushing you use does not allow free movement of the shock then the shock itself is still trying to bend every time the suspension moves. You already know the worst case scenario with the solid bushing. If your bushing at all restricts the degrees of freedom the shock needs you're placing a great side load on the seals and bushings around the shaft in the shock body. At best the shock isn't as responsive due to friction, at worst the seals wear more quickly. Shocks are not meant to be structural members of the suspension. They are not struts.

Don't get me wrong guys, I uh.... wonder.... about a lot of things I've seen on cars that have come out of that shop I'm just not going to flame Mike because my name is on these posts and I see him at the track most weekends.

I just don't let him work on my car....

Thanks for all the replies guys. ISC is sending me a new shock. I should have it no later than Tuesday June 6, 2006. I live in Canada so it takes a bit of time. I have a race June 9, 2006... so we shall see if I can make it.

I'm willing to give the guys at ISC a 2nd shot. The shocks/setup perform well on the track so I'm not just quite willing to give up on it just yet... I will follow Mike's advice and turn the washer/cup around so that it does not contact the delrin bushing but rather the bushing sleeve... and see what happens.

I'm going to be running brand new R comps on the 9th, 10th and 11th, rather than 4 year old Toyos so i'm pretty stoked to see how many seconds I can take out of my last year's lap times. Wish me luck.

Frustration comes from doing the same thing twice and expecting different results. I personally wouldn't want to drive hard into a corner with the thought of a shock breaking in the back of my mind.
At the very least find a stock rubber bushing for the shock. I'd hate to read your future post that might be titled, "Shock broke and I backed it into the wall HARD--- Car is a write-off"

Just my 2 cents worth(2 1/2 cents Canadian :) )

Would drilling some holes in the delrin help or perhaps just make a nice place for a crack to start?

Any chance you can give me some details on your car and the front dampers as well? Thanks.

I guess you could drill the bottom of the bilstein bushing sleeve to accept a zerk fitting and run grease into it every so often?

I wasn't thinking to add lube, but to increase compliance. A little air in there might reduce bind and flex of the damper.

Delrin is self lubricating and IMO drilling holes will make a place for a crack to start.

I would make the hole in the center bigger on each end and keep the center 20mm by rocking a drill bit around the hole. That way you would have a small 'bearing' area in the middle but have some movement at the ends. Then put something like a hunk of rubber on each side of the shock to keep things centered but not binding. Something to act like a big rubber washer before the steel one.

The opposite could be done on the outside of the bushing by rounding off the ends to make it sort of a ball shape(or a football with the ends chopped off) That way the shock could pivot around a little.

please listen to Damonb as he has the answer. the "shock" will need to move as the arc of the suspension moves, struts are solid since they help locate the suspension. this is why the oem setup uses a rubber bushing on the shock and why real "race shocks" will have a spherical bearing. The delrin setup will break something eventually and will likely wear out the seals and bushings inside the shock. a decent set of shocks will cost about $1200 to $1500 minimum. Of course the sky is the limit for shocks. Tein and some others make some nice stuff for about $1500 for the complete setup(shocks, struts, springs, and camber plates). I think I paid about $2200 for my custom sized and valved Biltsteins(not "yellows" street junk). If your running an EP car 2 grand for shocks is not likely to impact the budget to hard. these are expensive cars to build and alot of things will be more expensive. save yourself a big crash damge bill and buy some quality parts.

? I have installed my washer on my suspension with the bevel facing the center of the car. Therefore the flat part hits the sleeve (metal part) and the rubber is closer to the beveled edge.

(Metal sleeve should not move. Its the rubber bushing in the bottom cup that you snapped that should move around?)

I thought when were were at the track the weld is no good from what little I saw of it.

Not sure If I made any sense.

I looked at the bushing sleeve under a Stereomicroscope in materials lab at work. The weld seemed good. I think it was welded by resistance weld where bilstein spins the shock body up super fast on a lathe type machine and slams the bushing sleeve into the bottom of the shock body.

You can see the straitation lines from the failure spots. Lines that run like a barcode across the surface of the break. You can also see that when you put the two peices together they are not flush anymore and that the weld started to neck before it broke. One side was in tension and the other side was in compression when it snapped.

I agree. the suspension moves in an arc to allow for camber gain as function of suspension compression. What would really be bad if there was any bump steer causing toe angle change as the suspension moved up and down. The delrin bushing would not allow for any compliance for that...

Right now there is still some rotational compliance around the mounting stud. But that is the only degree of freedom for where the delrin bushing interfaces between the shock bushing sleeve, and the mounting stud. In reality you need minimum of 2 degrees of freedom at that bushing as I depicted in an earlier picture.

I'm surprised I've been the only one so far with this failure.

I believe all mass marketed shocks are assembled with the resistance weld method. On a street car installed properly with the correct springs for the application and a rubber bushing the shock should last for more than ten years of street driving. on a race car that sees limited use it may last for 5 years. alot of people don't keep race cars for that long and parts get replaced over time. In my opinion this setup is just not very good technically. It may "work" for short periods of time and good drivers can make bad cars fast at times. just because a car/driver is fast doesn't mean he has the best setup or parts installed. It maybe that the driver is much better than the competition and his machine doesn't have to be the best engineered.

http://www.teamfc3s.org/forum/member...view&car_id=78
sorry for the cross link.

But she's just a stock 89TII massaged a little for SoloSprint racing in Ontario Canada. Which is similar to your NASA Time trial HPDE type events in the states.

The front dampeners are stock shocks with the guts removed. THe body is then reworked to accept a Bilstein insert, which goes to a Ground control camber plate. I run 2.5in OD race springs. 10 inches long.

400 lbs in the front
250 in the rear
no rear antiroll bar.

I see your bilstein is from a BMW. On my FC, I run the old Mazdaspeed Motorsports kit and it came with Konis. I believe all the parts are sourced from AWR Racing. AWR racing is also now using/suggesting Bilsteins in their current kits according to their website. The Koni rear shock from my kit is from a Porsche 914 rear and the Koni number is 8241-1050. The koni I use still has the original rubber bushing from Koni. Mazda motorports supplies a larger diameter stud that replaces the factory lower shock stud. The part number is/was 0000-04-7214-AA.
I am thinking if you want to run Bilsteins (but not the factory replacement Bilsteins as the Porsche 914 struts have a much larger shaft) you could probably get the Porsche shocks and run the Mazda Motorsports stud. You'll have to check on the upper strut plate to see if that is the same though. On the other hand, you could probably contact AWR racing and see if they are running the same stuff as ISC racing or what Bilstein they are using because it does not say on their website.

Just trying to give you some more options.

-Jack

Speaking of options, and since this is a Bilstein thread, does anyone have any insight into what valving numbers one would specify during a custom revalve?

First, check out this thread on HybridZ that deals with adapting inserts to front strut housings. The first gen RX7 and the Z car are very similar in terms of front suspension design, and I imagine that even second gen guys might find some of the info useful.

Second, check out this PDF of Bilstein Motorsport dampers. While there aren't any RX7s on the list, there might be some cars that are similar enough to get some ideas from.

Third, look at this Bilstein stuff from a Volvo guy. Again, not the same car, but might offer some ideas.

Note that the Bilstein valving numbers are at .52 m/s and rated in Newtons (I think) while most domestic parts are rated at 3 inches/second and in pounds.

The reason I ask is I have a pair of P30-0102 inserts that I am considering using on my car. They are among the smallest (total height) inserts, and I will need to have them revalved and rebuilt before use. Any guidance, thoughts, contacts or information that I can use before I call Bilstein would be great. It is not that I don't think they can help, I just prefer to enter into any situation with as much information in my corner as possible.

I'd just send it back to bilstein to have them revalved for 65 bucks each. Call them and see if they have any info on the required bump and rebound dampening rates for a 1st gen rx7. They should have some.

All I can say is the ISC ones need ALOT more rebound dampening. Even just putting your weight into the shock you can see the shaft flyback up at great speed. There is very very little rebound dampening. But it seems like it has a lot of compression dampening

Well, doing that is one option, but I would like to know what they are talking about if I am presented with any options. Again, I don't doubt that they can do a good job, but with all the RX-7 racers here, perhaps I can get to something better than just good. Can you call ISC and see if they have the Bilstein valving numbers for the shocks and struts they provided you? That would give us a known baseline.

They just buy the bilstein dampeners from a distributor. Open the box. Throw away the box. Slide a threaded sleeve over the shock and then bolt the upper mounting plate on and ship it to me. It's an off the shelf part. Whatever a 1971 BMW 2.8L Bavaria's dampening rates are is whatever I'm running.

OK, but why did they choose that damper? It isn't like Senior Six BMW is a natural choice when looking for parts. Maybe it fits particularly well and that is all there is to it. I am just wondering if they had some inside info on the damping of those particular units because they really aren't one that would spring to mind.

I know that there is another company that says that particular Mustang rear shocks fit and work well on some RX-7s. I can see a situation where you are running your RX-7 on track, someone with a Mustang pulls a shock and you go "hey, that might fit my car and I bet the valving is stout because Mustangs are heavy." I've run with BMW CCA, and the chances of that happening with a Bavaria are about zero unless you knew Al Taylor when he was running his! See what I am getting at? Does ISC have a valving reason to use these shocks? Since you have the shocks, I was hoping maybe you would ask them. More likely to get a non-sales pitch answer than someone they don't know, like me.