Front brake reservoir

[dhighlan]

Have a new to me KTM 65 going through and redoing for Xmas and noticed the front brake not working. First try to bleed but can't get the system to prime, front or back bleed. Notice the system is gummed up pretty bad and deciding to get a rebuild kit as well as pull it completely apart to clean it thoroughly and something looked strange in the reservoir.

My question is in the 65 reservoir there is 2 machined holes in the bottom to feed the system. One is clear and the other looks to be almost through but not quite. It does go through because it will bubble under strong air pressure. I have never noticed before there being 2 holes on any other machine but can't say I have ever payed attention. Now I am thinking this maybe the problem as it is releasing pressure and not allowing it to build. Would there be any reason to have 2 holes because I can't think of one? It maybe it was drilled at first in the wrong spot and they drilled the second thinking it didn't pass through therefore would be fine. BTW the holes are 1.5 mm away, camera in the shop so I can't take a pic right now.

Thanks in Advance

[ossagp]

I have yet to rebuild a nissin cylinder for one of the CR's or YZ's, and never have done a KTM that wasn't magura. I have a couple of road bikes, that like many auto systems have two holes. those have two sets of packings. does yours have two sets?

[dhighlan]

Magura makes the clutches but the brake just say "KTM" so unsure as the clutch clear states "Magura".

No, it is a single set and I can't see how it could have two since the rear one (which is the open one) gets covered by the seal when pressed, sealing the back flow from the reservoir. The front one doesn't and would allow pressure to go back into the reservoir. I my mind I can't see how it could possible work that way.

[basanch73]

I have rebuild a lot of Nissin Cylinders, but haven't ever noticed two holes as well. However, with a bubble chaser profession, I would think that the second hole (if located behind the main hole in front of the first piston seal) would be a back up in front of the second cup seal in case the the first one should start to fail. If the second hole takes more force to bleed under pressure then I'd figure that to be it and probably an indicator to the rider as the brake input at the lever would most likely feel different. I'd really have to see the location of the cylinder holes and the pistons fluid passage pattern to be certain. Does your manual show anything?

Either way, if you just spray out the cyl real good and then put it back together and blead it thoroughly with your new piston, seal and spring in the rebuild kit, you should be fine. Heck, while your at it, go ahead and rebuild the caliper while your at it and you'll be amazed at the new brake feel.

Good Luck!

[dhighlan]

Well I received my stuff last night and I believe it is for volume. There is only one cup seal on the piston. The confusing thing is the second hole was almost completely closed so it looked as if the short stroked it when milling. The reservoir is one solid aluminum block so it is different than a Nissin. I was thinking the same as you on the second hole so I opened it a touch. But since there is only one cup I am think the hole and cylinder are so small on these 65's that they need 2 holes for volume. If the made one hole it would take up so much of the bearing surface the cup seal would snag and wear out prematurely.
No the book doesn't touch on anything like this at all.