YZ400 fork seal change


5 replies to this topic
  • B-524EVER

Posted August 17, 2008 - 09:42 AM

#1

Hey guys and gals, just bought a used 99 YZ400F, it has a leaky fork seal, is it easy to change these? Im a skilled mechanic, just never changed a fork seal on an upside down dirt bike fork. Do I need any special tools? Thank you!!

  • grayracer513

Posted August 17, 2008 - 10:08 AM

#2

You need one; a fork seal driver. Some will point out that they have successfully made their own from PVC pipe, but the real thing works much better, and there is less risk of damaging the seal. If you don't have a manual, get one here:

http://www.yamaha-mo...ice/manuals.jsp

If it won't download correctly, you can get a 426 manual here:

http://www.yamaha-mo...ice/manuals.jsp

The forks are the same.

>Loosen the fork caps and remove the forks.

> Drain the oil and remove the springs as shown, then skip ahead to the removal of the dust seal and the oil seal retaining clip.

> Follow the procedure for changing the seals, then skip ahead again to the refill process.

Quite simple, really. The removal of the damper assemblies from the lower fork tube is NOT necessary, although you can clean up the fork internals a little better that way. If you decide to do that, you'll need two more tools; a cartridge holder, and a 14mm Allen key.

  • B-524EVER

Posted August 17, 2008 - 04:12 PM

#3

:) THANKS FOR THE ADVICE, I THINK THATS A JOB I CAN TACKLE!! I WILL ADD THAT TO THE LIST OF PROJECTS ON MY 99 400F! FIRST IS GETTING IT RUNNING GOOD, CARB ACC. PUMP DIAPHRAM CAME OUT IN CHUNKS @@, IT STARTED BUT DIED AS SOON AS I TURNED THE THROTTLE!! :D

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  • grayracer513

Posted August 17, 2008 - 07:34 PM

#4

Turn your caps lock off.:)

  • BASSic

Posted August 18, 2008 - 09:59 AM

#5

Quite simple, really. The removal of the damper assemblies from the lower fork tube is NOT necessary, although you can clean up the fork internals a little better that way. If you decide to do that, you'll need two more tools; a cartridge holder, and a 14mm Allen key.


What do you suggest to use for a cleaner? Brake parts cleaner?

I'm about to disassemble and replace seals on two sets of KYB 46mm forks (YZ426 and KX250), and since they've never been serviced, I can't wait to get in there and see the mess.

  • grayracer513

Posted August 18, 2008 - 10:38 AM

#6

Fill the fork part way with clean mineral spirits. Work the main tubes and dampers several times and then dump it out and let it drain. Once you have the main tubes separated, take the lower leg/damper assemblies and put about a half pint of fork oil in each. work it through the damper and dump it out again. This will remove the remaining mineral spirits. The job will require about 34-36 ounces of oil, so if you buy two quarts, you should have enough.





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