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?