[dinsum]

Hi,

I just removed my 2019 fox 34 stepcast FIT4 because I got a new fork and looking to sell this one but I just found a problem with it that hopefully can be fixed...

When switching to locked out mode it was not doing anything, I could compress the fork fully. I tried cycling the rebound knob and the compression knob as I cycled the fork through its travel, now the fork lock out is working but it does not lock out until the fork is half way through its travel....

Any ideas on what I can try to fix this or what might be the cause of this issue? Any help is appreciated!

 

[evernorth]

Hi,

I just removed my 2019 fox 34 stepcast FIT4 because I got a new fork and looking to sell this one but I just found a problem with it that hopefully can be fixed...

When switching to locked out mode it was not doing anything, I could compress the fork fully. I tried cycling the rebound knob and the compression knob as I cycled the fork through its travel, now the fork lock out is working but it does not lock out until the fork is half way through its travel....

Any ideas on what I can try to fix this or what might be the cause of this issue? Any help is appreciated!

Hi,

That could very well be a blown bladder of your compression damper. They suck in oil over time and swelling a bit. Once they are to full, the blow up on a compression stroke. Can be fixed during a fork service from a suspension shop.

Ride on

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[dinsum]

You think it could be a blown bladder? Is there any other symptoms to a fork with a blown bladder? because the fork feels perfect in every way except for not locking out, rebound knob works perfectly as well

Its time for a lower leg service on the fork so I will tear it apart and see if anything is out of the ordinary

 

[294037]

Might not be blown, just some air in the damper. Air bubbles rise and the compression is at the top, rebound bottom. Also because the step cast uses a small 8mm shaft it doesn’t displace much oil through the base valve. So even a relatively small air pocket will take a lot of stroke to compress the whole way and put pressure on the compression circuit

 

[evernorth]

Might not be blown, just some air in the damper. Air bubbles rise and the compression is at the top, rebound bottom. Also because the step cast uses a small 8mm shaft it doesn’t displace much oil through the base valve. So even a relatively small air pocket will take a lot of stroke to compress the whole way and put pressure on the compression circuit

Ha good point as well. Didn't thought about the small displacement. Because in a regular non-sc fork, that would need to be a lot of bubbles that it takes that much travel. And that combined with bladders usually ingesting oil instead of loosing oil led me to the idea of a blown bladder.

Other symptoms would be less rebound adjust, less compression damping etc.
If you do a lower leg yourself, observe how many oil drops from the lowers. If a bladder is blown, there would be more oil in it then just the bath oil.

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[dinsum]

Ok was pretty easy getting the damper out.

yeah there was a little bit more fluid on in the damper side lower leg, so most likely fluid has escaped

First picture attached shows bladder with shaft fully compressed, second picture shows bladder with shaft fully out.

I completely cleaned the bladder with isopropyl to see if there was any leaks

As I was moving the shaft in and the bladder was expanding I noticed a very small amount of fluid coming out at the area I put in red in the first picture, I kept moving shaft in and out and there is for sure a really tiny leak there, I was also noticing a few very tiny bubbles coming out from that spot....

The weird part is if I grab the black shaft under the bladder and try twisting that silver aluminum piece where it is leaking from it actually spins..... maybe that piece needs to be tightened? or is it supposed to be able to spin by hand?

Thanks for the tips so far! much appreciated I am getting closer to figuring this out

 

[MTB Engineer]

The bladder lock ring is not attached to anything apart from a small lock ring keeping it from sliding off the bladder. Fox could have put a bit more thought into that. Mine also leaks from that arear enough that I need to rebleed the damper every 100h or so, even with a brand new bladder.

 

[dinsum]

Thanks for the reply MTB Engineer, Yeah the amount of fluid I seen coming out was very very minimal, I been riding this fork for 2-3 seasons before experiencing this issue so maybe its just a common issue that requires a bleeding once a year...? Are you also running the 34 stepcast fit4? or is this problem common for all fit4 forks?

Also how about do you go bleeding the system? does it just require me to remove some of those bits up at the top cap and fil with fluid?

 

[MTB Engineer]

Fox have instructions on their site on how to bleed the FIT4. You need their Mixmizer syringe, but otherwise it’s not very difficult just time consuming to get all the air out.

Mine is the 34SC Factory FIT4. I had no problems with my previous 34 but this one with the mew 8mm shaft is proving troublesome.

 

[dinsum]

Lol sounds like the exact same experience as me, I had a factory 34 before the 8mm S/C and no issues with it. Yeah I seen the instruction online for the 2016-2018 but thought maybe there was some differences, looks easy enough to bleed.

I guess my last question is do you know for sure which fluid the fox 34 s/c fit4 damper uses from factory? from what I gather its the 5w teflon fluid but would be nice having a confirmation because I always thought they used 20w gold fluid for some reason

Cheers

 

[MTB Engineer]

Damper should be 5wt R3 and 20Wt Gold for the lowers. The instructions online don’t directly apply for the 8mm SC version, but the main differences come if you’re rebuilding the damper. The bleed process is the same.

 

[dinsum]

Are you sure? Specifically under fox 34 step-cast part information on their website it says both FIT4 and GRIP damper use 5w teflon fluid, When I look up the regular Fox 34 part information on their website it says FIT4 uses 5w R3 fluid so I am pretty sure the fit4 stepcast uses the teflon 5w

I actually just got a reply from fox directly because I also asked them since I wanted to make sure, and they replied telling me it uses 5w teflon so I will use that since its what I got on hand anyways : /

I will dump all the fluid out to do a fresh fill, that way I won't be mixing fluids in case they put 5w r3 in it from factory.

 

[MTB Engineer]

5Wt teflon will also work, I have used it in my FIT4 as well.

 

[dinsum]

Just got all the oil out of the damper, actually ordered the 5w teflon last week still waiting for it to come in the mail before I can finish up.

The only thing that confuses me now is in the writeup for the fit4 rebuild on fox website, step 40 says when you are done bleeding the damper to make a mark 3 inches below the seal head and compress the shaft until the mark reaches the seal head, then proceed to put the top plug in to finish. Do you happen to do this? I wonder if the 3 inch length would apply to the S/C fit4 damper..

 

[seitenryu]

Just got all the oil out of the damper, actually ordered the 5w teflon last week still waiting for it to come in the mail before I can finish up.

The only thing that confuses me now is in the writeup for the fit4 rebuild on fox website, step 40 says when you are done bleeding the damper to make a mark 3 inches below the seal head and compress the shaft until the mark reaches the seal head, then proceed to put the top plug in to finish. Do you happen to do this? I wonder if the 3 inch length would apply to the S/C fit4 damper..

That 3"/70mm/75mm instruction only applies to dampers with 2 fixed ends. If it has the floating silver ring, you don't need to do that. The older design like the SC forks use, allows the free end to move as the bladder expands.

 

[dinsum]

Thanks! I will leave the shaft fully extended when I put the top plug back in and call it good!