yz400 fork tube question

4 replies to this topic
  • mediumdaddy

Posted June 15, 2012 - 07:47 AM


So i finally got my 99 yz400 back, and have went riding twice since. I've noticed there is a pretty good leak from the front right fork tube, so i asked my mechanic buddy about it, and he said they are nitrogen and oil filled and that he cant do the seals they need to be sent off somewhere. Is this true? i thought you could just replace the seals at the bottom of the tube? if so, how hard is this?

  • grayracer513

Posted June 15, 2012 - 08:23 AM


Your mechanic buddy is obviously not familiar with motorcycles. Your fork is not nitrogen filled, and motorcycle forks that use any sort of compressed gas are the exception, not the rule.

You can replace the fork seals fairly easily, although you will need to have a seal driver to correctly install them. There are several videos on YouTube about this process. The internal damper cartridge does NOT have to be removed for the job, although it's not a bad idea to do that so as to be able to clean out around the base valve. Look for a manual here:


When looking for videos, any YZ from '97-'04 or any WR F from '99-'11 will use the same procedure as your bike.

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  • mediumdaddy

Posted June 15, 2012 - 12:42 PM


Thanks for the reply - after doing a little research, what i am calling fork seals and what everybody else is calling fork seals is not the same thing. My fork is leaking at the very bottom, some seam about 2 or three inches up from the very bottom of the fork tube. not sure what it would be called. There's oil all over the tube below where the axle mounts. any ideas? Its on the side opposite the caliper, so im thinking its not brake fluid.

  • grayracer513

Posted June 15, 2012 - 05:39 PM


The lower fork leg consists of an aluminum axle mounting lug screwed onto a steel tube and locked in place with a big set screw. If it's leaking between these two parts, I'd recommend having a suspension shop correct that for you. It's a job an experienced and conscientious mechanic would be able to do, but one of the problems faced it avoiding thread damage to the lug, and damaging the surface of the tube by holding it incorrectly.

  • mediumdaddy

Posted June 15, 2012 - 07:55 PM


Oh good grief. This stupid thing is such a money pit! Not sure if i know of any decent shops around these parts.

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