KYB Bladder Forks

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#1
As I pulled down my first set of Bladder forks from a preproduction KX250 back in August 99 I was curious as to what the maker had intended when he unleashed this modern wonder on an unsuspecting market. At first I thought this was Kayabas attempt at making a "poor mans" dual chamber fork. I was later informed that it was designed to create a speed sensitive air spring similar to that of the sub tanks. The forks were essentially divided into upper and lower sections by two forms of seals at the top of the cartridge. On small (low speed) demands oil/air was supposedly able to bypass the seals, compress the bladder and give the illusion of a greater air volume. On high speed demands the seals were to present enough of a restriction to halt the transfer and create a high oil level feel. Whatever it was supposed to do it didn't exactly appeal to the masses. People complained of deflection, harshness and arm pump.
When testing new bikes if we wish to make a simple change to the compression stack we will turn the whole bike upside down and using an air impact wrench remove the base valves, make the change and ride straight back on the track. This allows the rider to evaluate the change while the previous setting is still fresh in his mind. After a short test session with the new KX we decided to do exactly that. Imagine my surprise when I pulled out the base valve and got showered in oil. Pressure had built up in the lower portion of the fork and air and oil was rapidly exhausted as I removed the valve. Now this was while the fork was fully extended and naturally pressure could only be expected to build even further as the forks were compressed. No wonder they had problems with harshness and deflection. Honda decided also to use the bladder forks on their CR125. After discovering the shortfalls of the Bladder Fork Honda continued to use the product only minus one of the seals. This completely negated any possible advantages of a speed sensitive spring. This didn't stop Honda from using the Bladder Fork in their sales blurb in an attempt to lure unwary purchasers. At least they had solved a problem. We had been performing similar mods with the KX shortly after its inception. Enter the KXF250. After a short stint with the much maligned cylinder valve Kawasaki have opted to head back to the bladder fork for yet another attempt at shooting themselves in the foot. One has to question "How many toes are left on the Jolly Green Giant"? Kayaba have attempted to solve the pressure build up problem in the forks by installing a check valve at the top of the cartridge. When pressure in the top portion of the cartridge exceeds that of the lower, the valve will open and equalise the pressure within the fork. It would appear it is upside down. The pressure still builds up in the lower cartridge area. Any attempt to reverse the valve however would see the system fail completely as oil would escape from the lower cartridge area much easier than it could get back in. After battling with the gremlins of this design for two days I decided to remove the seal from the top of the cartridge to see if this was still the fault of this fork. Well you can imagine my contempt for Kayaba as the rider came back with a grin on his face from ear to ear. Still, I guess this is a step forward however; It's a lot easier to remove the sealing band than it is to replace a cylinder valve. Good Luck
Regards
Terry Hay
 

steve125

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#2
Well put terry! :thumb: Thats what I have found with bladder forks also. I think it's best to remove the bladders and throw them in the trash!
 
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#3
Steve
I don't remove the bladder. I simply remove the seal and the fork operates like normal. Maybe ten years from now people will be removing a black congealed mess from the bottom of their forks, cursing me all the while.
Terry
 

Rcannon

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#4
Terry, do you have a website? If you dont feel comfortable posting it here, maybe you could e mail me with the information. I really enjoy what you post.

jamesc4085#msn.com
 

marcusgunby

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#5
I removed the bladder as well as the top seal, seemed to ride nice afterwards, air gap i think i set to 120mm , this was on a KX125 04.
 
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#6
RCannon
I don't have a website at this stage but we are woking on it. I've never really been into computers and my girlfriend is starting to get the sh-ts with how much time I've been spending on this forum. I really enjoy disscussing suspension with you guys. I only discovered this while trying to contact Eric Gorr and have been hooked ever since. Hurts your eyes after a while!!
Regards
Terry
 

marcusgunby

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#7
LOL terry a few tips from a expert , get a good chair-im on my 5th, get a TFT monitor as these a nicer on the eyes, get a broadband connection as it makes surfing faster, on the girlfriend i have no answer-been trying to train mine since Jan 2000 and she still throws stuff at me:(
 

steve125

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#8
Terry I feel if you remove the seal and just leave the bladders "in" you will loose two things in the process. One:with the bladders out, you will have increased the oil capacity and thats got to be a good thing. Two: by just removing the seal you have effectively just lowered the oil level height during low speed fork action. I don't feel this changes bottoming resistance, but it does soften the early mid stroke as the bladder is in the process of collapsing. With just the seal out the bladders are still working, that can't be good. Thats why I just pitch the bladders and the seal and set the forks at a normal oil level.
 
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#9
Steve
My intended purpose in removing the seal is simply to remove the barrier that divides the fork and allows the flow of oil/air to function as normal. The volume of air within the bladder is still subject to the same compressive forces as the rest of the air within the fork. By removing the seal we have eliminated the high/low speed effect the manufacturer intended. With the bladder in place we run the normal oil level for that design which I believe is 90mm. Without the bladder I would compensate by reducing the height. I think we are both achieving the same result with different methods. But you are right and certainly removing the bladder would allow you regulate oil heights with a known volume. I'm curious as to what you thought when you first saw these forks apart? As I mentioned in the post that I thought at first glance Kayaba was attempting to produce a cheap dual chamber. My initial conclusion based on this assumption was that the system was bound to fail due to the fact that the damper rod was not sealed against the top of the cartridge. Oil was bound to escape more easily from the lower portion then it could get back in and we would end up with an emulsified mixture within the cartridge. After I was informed about the "speed sensitive" air spring I had to re-evaluate but still came to the same conclusions regarding flow. In order for the speed sensitive air spring to work effectively I believe we would need to allow a bit more oil to bypass the seal around the cartridge. This could perhaps be achieved and made adjustable by a replacable bleed jet similar to that of a two stroke carb main jet, positioned in the spring seat at the top of the cartridge. Any thoughts?
 

steve125

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#10
Terry, with the forks apart and in theory, it all looks good. But as you know on the track it's a different story. With the RB (restrictive barrier) washer removed the mid spike was gone, but the forks dived too much. After the Bladders were also removed and oil level re-set, the forks had a firmer and more progressive feel. I know of a RT dealer that has tried drilling the RB washer with little or no success. IMO the best way to go about all this is the Enzo canisters!
 
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#11
Steve
I have never used the ENZO cannisters and I am unaware of any positives or negatives of this concept. I know the Kawasaki team over here tried them this year and then decided to do away with them. Regarding the bladders creating dive I'm a little confused. If the total air volume is identical in both situations then the pressure differential between extended and compressed should also be identical wether the bladders are in place or not. My ideas regarding a bleed jet are not something I wish to commit to practice. Just a concept for fixing something that doesn't work.
Regards
Terry
 
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#12
I think I may have been the original dissenting, doubting Thomas of the bladder on this forum. Argued with Jer more then once and got my butt chewed for calling them a gimmick here. I have been pulling them out and throwing them in the trash for quite awhile. They have made little sense to me since their inception. I tried working with them at first as everyone else did but I got tired of them in hurry.

I'm glad to see somebody else shares my opinion of those wretched pieces of scrap. Oh, and just for the record AGAIN...I also think the bumpers are subpar. I do find these more acceptable to work with though, but I'd take a properly toleranced hydrualic cone any day over the bumpers.
 
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#13
Shocknut
As I mentioned in the cylinder valve post, I believe the bottom out bump rubber gets a bad rap. The fault in the cylinder valve forks is not so much the type of bottom out system, but the fact that it reaches the bottom out system in the first place. If you are keen to try them I will happily send a set of our cylinder valve replacement kits, This will advance KYB fork technology forward to 1997 and be a major improvement from their latest configerations. You will have to revalve the base valve to suit the new oil flow rate. This will allow you to evaluate the merits of the bottom out bumper on its own without the detremental effects of the cylinder valve.
Regards
Terry Hay
 

steve125

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#14
Originally posted by terry hay
Steve 
Regarding the bladders creating dive I'm a little confused. If the total air volume is identical in both situations then the pressure differential between extended and compressed should also be identical wether the bladders are in place or not. 
Terry it is my understanding that with the RB washer and seal "in" it in effect separates the two chambers, upper and lower. That is untill the pressure from under the RB washer blows (mid spike) :scream: . This being the case it's easy to see why the forks dive more with the RB washer out and even more so with the bladders left in.  Now you have a single chamber with a bladder collasping making the oil level even lower, untill the baldder is done collasping. I feel this all happens very early in the forks stroke. :confused:
 
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#15
Okay
And there is where the confusion lies. I'm talking about the bladder being in or out after the seals have already been removed where you are talking about the difference before and after the removal of the seal. Cool!
Catch you later
Terry