Fox 40 Dampener Technical Advice Needed

I have two different Fox 40s that have two separate dampener issues that I am trying to figure out how to fix. I have experience replacing blown dampener bladders, but I have never had a dampener apart at the seal head, (or the middle of the shaft).

Failure 1: 2009 40 RC2
Replaced a blown bladder and after replacing the bladder, the rebound then worked properly, but we noticed there was NO compression dampening when the dampener was compressed regardless of hi or low speed compression settings. I never had the seal head apart or to my knowledge messed with anything in the compression part of the dampener. (I am under the impression that the bladder part only is for rebound dampening).

Failure 2: 2006 Fox 40R
Rebound dampening stopped working completely regardless of rebound setting. After replacing two blown bladders recently, I assumed that this was the problem. When I took the lowers off I was surprised to see the that the bladder was not poking out past the cap. I went ahead and removed the bladder and It appeared to be in perfect condition. I went ahead and replaced the oil under the bladder, bled it out, and installed a new bladder and cap hoping this might fix it. Rebound dampening worked slightly when the adjustment was turned all the way in, but after several minutes of riding the rebound dampening stopped functioning completely.


I have been reading Fox's dampener service instructions on their web site but I am still a little confused about what could be causing each problem. Could the rebound dampening failure on the 2006 40R could be caused by a worn Rebound Glide Ring as shown in this picture:


It does not say what that blue o-ring on the tip is but I was thinking maybe that is for the compression dampening? Thanks for any Help!

One More Question: I just replaced the bladders in each of these forks. Will I be able to leave the bladder and cap in place and just take apart the dampeners at the seal head to perform the needed repairs there?

daisycutter said:

http://www.enduroforkseals.com/id152.html

Using the search function I found these replies which maybe helpful.

http://www.ridemonkey.com/forums/showthread.php?t=234814

Yes you have blown the bladder. You may not have noticed a loss in damper performance because not much oil has leaked out of the damper yet. The cartridge rebuild kit, which has a replacement bladder (along with many other o-rings) should run you about $35~40 and you'll need some 10wt oil to do the rebuild. You don't need shaft clamps, but they do make the job easier. Fox has good detailed instructions here: http://service.foxracingshox.com/consumers/index.htm

I've had pretty much every single generations of 40's since they first came out years ago and only had ONE blown bladder.Im not sure what actually causes this but numbers of people Ive met with the same issue are usually running no or very little compression.Once they've used all of the available travel, there's nothing to prevent a sudden rise of pressure inside the bladder and then BANG!...

Click to expand...

I used the search function and the thread that you referenced was a previous thread of mine in regard to a blown bladder issue that has since been fixed. I am asking about other dampener issues that replacing the bladder did not fix. I want to learn what inside the dampener is causing these issues, so I can be sure that I am repairing it properly.

I haven't called Fox yet. They usually put me on hold for 15 or 20 minutes and I'm very busy during the day. I'll try to call them as soon as I get time. I feel confident that I installed the bladders correctly and the bladder lip is seated properly inside the cap. I have replaced them in the past. The 09 40 now has properly working rebound after I replaced the bladder, I think the compression was blown already before I even took it apart. The 06 40, it seems the bladder was never even blown and something else is causing the lack of rebound dampening.

troy said:

Worn glide ring may cause lack(or lower range of adjustment) of rebound damping. Oil passes the piston through the gap between cartridge tube and glide ring so there is no enough oil to flow through the rebound bleed hole (it controls LSR). IIRC blue glide ring seals/guides bottom out system - worn gl > less progressive damping > higher pressure in the system > blown bladder .

Click to expand...

Thanks! That is exactly what I was looking for. I wonder if the blue glide ring is worn and causing the lack of compression dampening on the 09 40.

Socket said:

That blue glide ring is only for the hydraulic bottom-out, it doesn't affect compression except in the last inch or two of the stroke.

I have seen the lip on the rebound pistons bend or break off before, completely losing/destroying the glide ring, which caused the symptoms you are describing. I kinda doubt you've just plain worn it out enough for things to be that significantly wrong, but hey if you ride 5x a week and have done for the past 4 years then this might be the case! In any case, chances are that it is something to do with the glide ring not sealing properly, either because it's worn out, broken up, or the piston lip has shat the bed and dumped the glide ring altogether.

As for the lack of compression damping, this may sound a bit rude but it's entirely possible that this is the first time you've actually noticed that the compression adjusters on some 40s actually do almost nothing since the stock valving on them (up until 09, not sure whether those had the old super-super-light valving or not) was so light! If you're 100% sure that you were able to get significantly more compression out of them before rebuilding, then you need to pull them apart again and check the compression assembly. Particularly, take note of how many shims are in there - if it's only one then you still have the old-style valving that was pretty much zero compression damping across the board. Newer ones had 4 or 5 shims of various sizes, from memory. If you do have the 4 or 5 shims in there, then you need to be disassembling and checking all the parts in there.

Click to expand...

Thanks, that is very helpful. I guess I need to take both the dampeners apart and take a look at everything. Now I know what I need to look for.