Question for Shock ('damper') experts

kbsilver · Post by **kbsilver** » Tue Aug 11, 2009 7:31 am

All, It seems as that on the 540, the heavy front end (with the 8-cyl) and the very high rate springs is just plain hard on shocks. I replaced the shocks on our 540iT with Koni FSD's a while back to get that blend of sporty control with tolerance for our bad NJ roads. At first they delivered exactly what I wanted. 10K miles later the car started to become floaty, now at 20K miles later they are completely shot!!! Like riding a pogo stick at times.

I must say very disappointing and certainly not a good testimonial for Koni (and these were expensive!).

Now looking for replacement again and my choices are Bilstein HD's or OEM. Am still looking for control and comfort, do not want a kidney or spine killing ride. I know the OEMs will deliver that, but will probably only last 50K miles. Will I be unhappy with the Bilstien HDs, which would hopefully outlast the car? They have a reputation for being quite firm, but I'm thinking this will be balanced by the weight of the front end. This is where I need the expert advice

.

(Think I want HD's, very conflicting info as to difference between Bilstein HD & sport regards to valving and shock length, but believe the HDs will work with factory sport springs, where sport are required for lowered springs).

jnscaldwell · Post by **jnscaldwell** » Tue Aug 11, 2009 7:50 am

I had the Bilstein HD struts on my E36 and I loved them. I ran it with stock springs and had no problem. I do believe you need to run a "sport" spring with the Bilstein sport shocks. One nice thing about Bilstein is they do have a revalve service and if you really want to get technical you can provide them with more details about the car (spring rate, etc) and they can custom tune the struts/shocks to your specs. Here's the link to the Bilstein service page

http://www.bilsteinus.com/services.php

Hope this helps complete part of the puzzle for you.

Edit- I forgot to mention the ride was comfortable with the HD struts and shocks. Felt sort of like a compromise between stock and sport. Tight enough to be fun but not enough to loosen your fillings!

cgraff · Post by **cgraff** » Tue Aug 11, 2009 8:29 am

One thing to consider... if I remember correctly, Konis have a lifetime TRANSFERABLE warranty whereas Bilsteins do not. And Bilstein won't warranty their custom valved shocks either.

I'm surprised the FSDs went as quickly as they did. My suggestion is to call up Koni and complain. In my experience, I've had Bilsteins go bad through poor design very quickly - their top seals seem to fail pretty often. In fact I had two front sports blow out in 10k miles. This is on an E28 mind you. With Koni, their longevity is really good - at full stiff settings I had rears and fronts lasting 40k - again on a modified E28. However, I know that Koni has some QC issues every now and then - a friend who was putting on FSDs had a defective unit brand new, but Koni was more than helpful in getting them back on the road.

This is in fact the first time I'm hearing that FSDs have lasted so few miles. I don't think Bilsteins would last all that long on your car either. But that's just my experience.

Ironically, I think if they had them available, Bilstein Comforts would have been your best compromise.

-Chris

kbsilver · Post by **kbsilver** » Tue Aug 11, 2009 10:04 am

Think Koni warranty is transferable because they do not ask for purchase documentation. If you own the shock, it has a warranty. Koni agrees the shocks should last longer then 20K miles and are happy to replace the units if I ship them back. I just do not want to have to do this every 15K miles!!

Do not believe they are individually defective, just not up to the task in their inherent design. The FSDs just do not seem as durable as other Koni products. There is chatter on the news boards of others having short FSD life (but I may have the record).

Planning on using a standard shock, nothing custom, so no issues there. There are very few shocks available for the rear of an iT with air suspension. Interestingly enough I have FSD's on the 328, with much more mileage on them and they are still fine. But then a lot less mass needing to be dampened in the 328, especially in the front.

kishg · Post by **kishg** » Tue Aug 11, 2009 10:05 am

Definitely check with koni on warranty replacement. Bilstein HD with stock springs should give you a good compromise. There's also the Bilstein B14 coilover kit to consider.

kbsilver · Post by **kbsilver** » Wed Aug 12, 2009 3:21 pm

Doesn't look like Koni Warranty is transferable after all. Plus they want a copy of the invoice before they will talk to you. Couldn't find it anywhere but remembered where I got them and they were nice enough to email it to me.

So I discuss the situation with the warranty department and explained that I really did not want to replace shocks almost as often as I changed oil, even if they are under warranty. The person I spoke with understood, and agreed to replace them (fronts only) with Koni Yellow adjustable sports. Hey a WIN-WIN, and Koni has redeemed themselves for me. (The original FSD's are actually more expensive than the yellows, so they made out too). Of course don't have them yet but sure looks like we're on the right track!

PS. Rear shocks are not a problem on the iT with the air springs. The shocks do not work very hard and never wear out. The whole rear suspension on the iT is weird especially because of the air springs which are very non-linear, and do not compress much.