[Da Peach]

Hi,

My GF just picked up a used (circa '03) Santa Cruz Blur. It came with this fork

We kicked the tires and gave it a ride around before we bought it and all seemed A-OK.

But last night, after pedalling around in the rain, we brought it inside and could hear a hissing sound coming from the top of the left leg (air cap).

If I load up the fork just standing there, I hear a sustained hissing. The fork doesn't drop detectably, but as long as I maintain pressure on the fork, the hiss continues.

Is this "one of those things" that just happens with an air fork after a while? Should we get it rebuilt? Or is this just some silly "loose nut" problem.

I was pretty surprised because the folks we bought it from seemed to be pretty fastideous bike folk.

Advice?

 

[HAB]

I can think of a few things, off the top of my head. First would be the easy stuff, either the air top cap is loose, or the valve core has worked its way out a little. Try tightening both of those up first. If those don't work, and the air really is coming out of the top of the crown there, about the only other thing it could be is the o ring under the top cap. Depressurize the fork, unscrew the top cap, and take a look. If the o ring looks damaged, replace it. You should be able to find a suitable replacement at a hardware store, or you could just get one from RS, though that would probably cost more and take longer to get.

 

[Da Peach]

Thanks. I'm not too familiar with fork guts, so I'll need to DL the manual.

This all sounds like its right at the top of the fork, right?

 

[HAB]

Yeah, all at the top. Here's the basic run down:

The way the spring works is that there's an aluminum cap that threads into the crown, with a schrader air valve built into it. (Come to think if it, I forget if that particular fork has the whole valve assembly threaded into the top cap and sealed with an o ring, or if the outer portion of the valve and the top cap are all one piece. If it's the former, there'll be wrench flats at the base of the valve, and that's one more thing to check for tightness and a bad o ring.) Anyway, that top cap is made air tight by an o ring at that gets squished in between the top cap and the crown. Below that, there's a bunch of empty space (the air chamber), and the bottom of the chamber is formed by a movable piston that's attached to the bottom of the fork lowers by an aluminum shaft. When the fork compresses, that piston is forced upward, compressing the air in the chamber.

So in short, if air is leaking from the top end of the fork, it has to be involved with the top cap some how. All you need to do to take a look is to take the air out of the fork, and then unscrew the top cap. I want to say it's a 24mm wrench, but don't quote me on that. In any case, it's some sort of standard box wrench. Make sure that cap was tight, that the o ring above the threads isn't mangled or out of place or missing, and that the valve core in the cap is tight. You'll need a valve core tool for that. You can also check if the valve core has just gone bad by swapping in one from an old schrader tube or something like that.

 

[Da Peach]

Alright.

Step 1: Get home
Step 2: Re-read all of this
Step 3: Don't screw it up.

Thanks man!

 

[HAB]

Sweet, good luck. Let me know how that goes/ if you've got any questions.

 

[Da Peach]

Yep, it appears to be leaking from the valve core. See the bubble right above the "02" in the date?

Just not sure if my shock pump will work with this thing...

Edit: yep, the pump works

Edit again: just not sure how to get the top cap off now

 

[HAB]

Ooops, didn't realize this is a uturn. I thought it was a solo air. Anyway, you don't need to take the top cap off. Just get a valve core tool and snug that up.

 

[Da Peach]

Cool.

This is the fork

Now I need one of those tools. Let's hope the 'ol LBS will help a brother out.

Thanks a bunch HAB. I was worried I'd bought a lemon...

 

[HAB]

You'd actually probably be better off trying an auto parts store. This isn't anything bike specific, just your standard schrader valve core tool.

 

[zebrahum]

Just a thought, that looks like it's leaking around the valve stem, not out of the core. It's still worth trying the valve core tool, but you're probably going to need to put the new o-rings in. A kit should be available from any bike shop if you're willing to wait a week or so.