Headshok, elastomer completely perished

[Nico]

Took out the damper from my Killer V 800 (98 model).
I expected to find an elastomer that was just so much compressed that it had no life in it anymore.
What I found was a tube full of small bits of perished elastomer.

I cannot get this stuff out without contaminating the needle bearings so I will take out the bottom plug.

But first I have to finish another rebuild before I will continue working on this one.

More on this situation as the information becomes available.

 

[IdahoBrett]

Hopefully a good flushing with something like mineral spirits will clean all those decomposed elastomer bits out…

 

[IdahoBrett]

Makes me think I better service my headshok sooner rather than later. Mine is a decade newer. I wonder at what age or use the seals degrade to the level yours did.

 

[black lightning 1987]

The elastomer in the XS800 that I have apart was completely dissolved into bits as well. Do you have a source for new ones?

 

[Nico]

Thanks for asking

I found a company that sells 25 mm round, 1000 mm long elastomer bars.
No idea if the material have the right specs.
But it is not that expensive so I am willing to buy it to see if it is suitable as a replacement part.

If it works for me it will also work for other Cdale dampers were the damping material has perished

 

[black lightning 1987]

What is the price for what you found? There may be some options here but they aren't exactly inexpensive:

Cannondale Headshok DD25

Make your Cannondale HeadShok ride like new! Our Elastomer Refresh Kit will replace your worn factory elastomer. This kit will fit the DD25 HeadShoks that were used on Silk Path D, Silk City D and Silk D forks.

www.suspensionforkparts.net

 

[Nico]

Ow sorry, I thought I had mentioned the price for the elastomer.
A 1 meter bar is sold for around $10,- ex shipping.

Next week I will order one of those elastomers to see if it is the right size and material.
I will let you know about my findings

 

[black lightning 1987]

Thanks. I've been going to search for alternate sources but haven't gotten around to it.

 

[Nico]

Some updates from my side.

Attached an image of 2 types of dampers.
On the left a DD50, this is an oil cartridge with lock out and damping.
This one I used in a Silk Road fork with more than 25 mm travel, I think I made it like 40 mm.
The frame is scrapped because of small cracks in the seat stay and it was no longer safe to drive.
If you can enlarge the image you can see that the elastomer that came out is also finished since it is full of cracks.

On the right an EDM/MC50 that came out of my Killer V800 with the perished elastomer.
Next step is ordering some PU elastomer and cut it to size.
That last part will be trial and error for the size of the elastomer since I can't find any technical specs for a 50 travel fork to what size it should be.

 

[Nico]

Surprise, surprise

Never expected I would find a spring inside my fork.
Maybe that blue that you can see on the image with the internals of the fork should have been a heads up...

Anyways, I ordered the 25 mm elastomer anyways, so lets see what that brings.

 

[black lightning 1987]

Which bike had the spring? The XS800 cyclocross fork also has a spring.

 

[Nico]

I pulled this spring out of my 1998 Killer V800.
Initially I thought it had just an elastomer serving as spring/damper.
But I found the spring and what is left of some kind of, I guess, polyurethane.

But there is more work coming up.
As you can see on the first image I posted, the blades from the needle bearings have moved up.
So I want to disassemble the fork to fix the issue with the blades.

 

[black lightning 1987]

I have all four races slipped out of position on an F500. Haven't gotten around to looking into that one yet.

 

[Nico]

This weekend I rebuild the headshok, the bearing blades are now were they are supposed to be.

Also last week the 1 meter elastomer bar arrived.
Unfortunately it's size is 25,6 mm so it is to thick to for the fork tube.

With a small grinder i got it to 24,0 - 24,5 mm.
It feels quite stiff so I decided to make a couple of notches to make it a little thinner and more flexible.
Right now it look like I have not taken enough of so this could mean I need to look for another supplier.

For those of you who know something about hardness, the material is 90 shore A.

I will do some more work on it to see if I can improve the compressibility.

 

[Nico]

Today I remodeled the elastomer a bit more so it can compress better.
I have put it back into the fork and it compresses and has some travel.
It the weather is ok, I will take the bike for a short ride.

 

[black lightning 1987]

I kike you approach to the problem. When I worked in motor racing we often changed "bump rubbers" and would saw them shorter when that seemed to be advantageous for the conditions. The race car elastomers were typically conical for about half of their compressible height. I don't remember trimming one other than in height, but we had different durometer elastomers to work with.

 

[Nico]

Ow wow, never realized it has been so long since my last post in this topic.

Here is an update.

That piece of elastomer I got was not performing well.
Even though I shaped the bar in the hope it would make it more flexible, in reality it is just way to stiff and is not giving any damping at all.

In March I made a first 3D design but was to busy to print and test it.

Two weeks ago I was able to do a first test which failed, the 'spring' was to soft and it compacted under the weight, so practically I had no travel in the fork.

So I made a new design and I just made a test drive and again it is a bit to soft but it was way better than my first design.


I think the optimum will be a tougher damper with maybe a few tiny holes to let air in and out the inserts.

 

[Nico]

After my optimism, reality struck.

A longer test ride with the 3D printed parts showed that the parts slowly buckle.
When I took the parts out of the fork, each of the three parts has shrunk about 3-4 mm's and there is hardly any elasticity left.So this was a fail.

The next experiment. I do not what yet but as soon as there is something to share I will let you know.

 

[black lightning 1987]

Wondering if you could trim down race car "bump rubbers" and make them work. Not sure who made/makes them but I would try Koni first.

Koni Bump Rubber 7034530000 | eBay

Find many great new & used options and get the best deals for Koni Bump Rubber 7034530000 at the best online prices at eBay! Free shipping for many products!

www.ebay.com

Not exactly inexpensive to experiment with. Perhaps you could find a Formula Ford racer nearby who has some used ones. The shaft hole is likely too large but that might not keep them from functioning.