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Old 03-25-07, 06:41 PM   #1
chryst
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New stumpjumper, blown fork?

I just bought a brand new Stumpjumper comp today. It has a Fox F-90 RL fork. The guy at the shop pumped it up so the sag was correct, they checked all the other stuff, and I rode off.

Took it on a 10 mile ride, nothing too tough. Got home, and after about an hour, I hear a pop-hiss noise like a tire blew. I look at the fork, and the dust seal on the top of the left fork is blown up the tube. WTF? I screw on my shock pump, and there's about 1/2 the pressure in the fork. I sit on it, and it sags a lot more. Seems an air seal or something blew.

I don't know much about forks, so I'm asking you guys.

Obviously, I'm taking it back tomorrow, but I'd like to know if the fork's blown, or if it's something I did that might have caused it? I don't think I hit anything hard enough on today's ride to even bottom it out, but I suppose its possible.
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Old 03-25-07, 07:09 PM   #2
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eh sounds like a warranty issue.

the dust seals can just come off but it shoulnt let air out, so you shuold expect to get a new fork

hopefully the shop wont have your bike for long
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Old 03-25-07, 07:16 PM   #3
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eh sounds like a warranty issue.

...you shuold expect to get a new fork

hopefully the shop wont have your bike for long
That's what I was wondering. I fear they might either find some explanation of how it was my fault, or that this is some common maintenance thing where they replace the seals and I wait for it to happen again.

I'd much prefer the new-fork option.
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Old 03-26-07, 03:02 PM   #4
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Ok, update, and it's kind of what I was afraid of. The guy at the shop put 100lbs of air in the fork this morning, and it's held all day. So he can't replicate the problem, and says he can't do anything warranty-wise.

Should I accept that and hope for the best, or do I become a hard-ass about it and demand a new fork?
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Old 03-26-07, 03:09 PM   #5
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Make sure the complaint is documented. Check to see how lemon laws apply in your area.
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Old 03-26-07, 03:40 PM   #6
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Demanding a new fork would be a bit extreme....

It sounds like there isn't any oil (or not enough) in the air chamber. This would allow air to seep past the piston and pressurize the lower leg area. This excess pressure could easily blow the dust wipers out of the lowers.

The thing is, the problem won't happen again if the fork is just left sitting. You'll need to test ride it to be sure.
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Old 03-26-07, 03:49 PM   #7
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Well, there's definitely oil in there, cause a cc or 2 of it of it blew out with the dust cap. I guess the level being low is a possibility. Is that something I can check myself, or should I rely on the shop to do it? If they're not checking these things, is it a sign that the mech just doesn't know his stuff, or is that something I shouldn't expect him to know?

Sorry for all the dumb questions. I've always been happy to just take things apart and figure out how to fix them myself, but forks are a good deal more complex (and expensive) than a bottom bracket, so teaching myself all about them that way doesn't seem like a great idea.
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Old 03-26-07, 03:53 PM   #8
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eh sounds like a warranty issue.

the dust seals can just come off but it shoulnt let air out, so you shuold expect to get a new fork

hopefully the shop wont have your bike for long
no, you shouldn't expect to get a new fork. warranties are repair or replace at the manufacturer's discretion. this problem can be fixed pretty easily. the F-90 RL is a pretty simple fork on the inside, and the suggestion that Svr made sounds like the correct solution.
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Old 03-26-07, 04:05 PM   #9
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Well, there's definitely oil in there, cause a cc or 2 of it of it blew out with the dust cap. I guess the level being low is a possibility. Is that something I can check myself, or should I rely on the shop to do it? If they're not checking these things, is it a sign that the mech just doesn't know his stuff, or is that something I shouldn't expect him to know?

Sorry for all the dumb questions. I've always been happy to just take things apart and figure out how to fix them myself, but forks are a good deal more complex (and expensive) than a bottom bracket, so teaching myself all about them that way doesn't seem like a great idea.

the air side of the F90 RL should have about 15-20cc of 7 wt. oil in the lower leg, and about 5cc of float fluid (like a liquid grease, a bit thicker than phil's tenacious oil, dumonde tech makes something very similar in both color and viscocity) on top of the air piston.

the main purpose of the oil in the lower leg is to lubricate the bushings in the lower casting, this is also the function of the foam rings that rest under the dust wipers at the top of the lower casting. it's a pretty simple operation to perform, you just need the oil, the float fluid a measuring device (a syringe like you'd use for a brake bleed will do), a 10mm open ended wrench, and a 26mm socket for the top cap. make sure you let all the air out of the fork before you open anything up.

there could be something more involved, like a seal on the air piston itself might be blown out (not very common, especially for a brand new fork). i would recommend taking it to the shop and having them take a look at it to so you don't void the warranty by opening it up yourself (fox is very particular about who works on their forks). also, they can get it out to fox asap if they need to.
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Old 03-26-07, 04:52 PM   #10
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Awesome, thanks so much for the info. I'll definitely have the shop do it, since I'm not keen on voiding the warranty.

I stopped by the shop, and asked them to check the oil levels in the fork, explaining my reasoning. One guy thought that was a good idea, the other guy seemed skeptical. Lucky me, the skeptical guy is the one actually working on my bike, but hopefully he'll check things as I asked, and top up any fluids.

I'm picking it up tomorrow, riding on Wednesday, and with any luck, things will be solved. If not, I guess I can take it to a different shop or something.

I'm just really frustrated, cause that's $1700 on my ccard that I should be out riding.
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