Ok, to start things off, this is a supplement to what Hayes offers on their site in the file HFX-9 MC-45-20068.pdf. I’ll also show a few common points of failure. This brake was taken apart after only one season of mild XC riding (mind you it sucked since day 1).
Below is an exploded view of what you get when you take it all apart. Bleed it dry first to avoid a mess when taking it apart.
To take off the line, slide off the dust-cap, unscrew the bolt, slide it down, and yank it straight out. Be careful not to kink the hose. Below is a view of it semi-exploded. This is also how it ends up going back together. (Note the ovalized washer)
Below is a better view of the same.
The instructions say to take it all apart, clean it with isopropyl alcohol, look for worn parts, and put it back together. Quite easy actually, except the snapring.
Below are some parts that end up getting warn out; mainly the washer, sometimes the balljoint too.
Note, again, that the washer is just junk. The balljoint goes through it with very little force. The burrs on its inside edge make for a very unsmooth lever feel, its jumpy, unprogressive, and tends to stick. Hayes notes to add verilube/grease to the balljoint, and this helps, but a new good washer helps a lot more.
The snap ring can be bent back flat with your hands, but the res cap is torn here, and it doesn’t look like anything can be done to restore it. It leaks a minor amount of oil because the cap doesn’t seal it completely. (Note, to avoid this, use proper bleed kit adaptors)
The main cylinder O rings below don’t seem to be worn at all since the dot3 keeps them lubed and sliding nicely.
The pictures below are of the cylinder body chamber and res. Note that there are two holes from the cylinder chamber into the res, and 2 more through the res cap, (not shown) but only one in the res cap can be sealed via the bleed hole plug. I suppose this helps if your oil pressure is really really high for some reason, it will auto leak through the lever instead of busting your hoses..?
After you have the cylinder re-assembled and dropped into the body, the fun begins. Without a snapring tool, this can be a pain. Squeeze the pushrod in to take some pressure off the snapring, and position it so it looks like it’s in the right position. Then, push it in with a small flat screwdriver into its groove. It should snap in on one side, then do the other. It takes a few tries to get it right, so be patient.
These are the 2003 HFX9’s, and it doesn’t look like anything has changed in 2004 save for the logo on the body now says HFX NINE.
Hayes HFX-9 rebuild written and photographed by Ashek