MotoUtah: Motocross and Off-Road Riding in Utah

Im pretty good when it comes to working on bikes and fixing them up, but I just got this KTM MXC and am having a terrible time bleeding the rear brake. It pumps up and feels fine, but when I take it up and down the street, its non exsistant. I bled the brakes and put all new fluid in it and it still does the same thing....

I did the same to the front, and they work great, plus I bled the clutch and it seems to work good too. so this is leaving me scratching my head!!!!

Any sugestions?

It almost sounds like you haven't got all the bubbles out of the brake line yet. I had the same issue with my car so I bled them a few more times, then they started working properly.

...or the master cylinder is due for a rebuild. Also you could look at the pads to see if they are glazed

Try pushing the piston in all the way and then pumping it back up, not sure why it works, but it has for me in the past.

I'm with Mark. Prob need to rebuild your master cylinder. The cup will get a slit or hole and then its hopeless. Also it helps to get the calper above the master cylinder.

I had a similar issue myself recently with my street bike on the front. While I agree it could be the cup on your master, usually if you listen close you can here it suck air.
Here are two tricks I picked up from a Honda wrench I know that fixed mine despite putting over a bottle and a half of fluid thru it with no results.
1) Ziptye or otherwise keep your brake on overnight. This way, any bubbles in the system can move up to the cylinder. While doing this it also helps to tap known problem areas for air bubble (banjo bolts, cylinder base, etc) with a plastic mallet. I emphazize tap, don't take your frustration out here.
2) If step one didn't work, try removing the entire assemble and then hang vertically overnight with cyclen up and caliper down, tapping here helps once again. With a straight shot it seems to move bubbles thru the system better.
One other thought, are you sure your bleeder is closing and seating properly?
Good luck, I know how incredibly frustrating that can be.

fmxrider wrote:


I think thats backwards. The air needs to escape through the bleeder. So hang vertically with the caliper up and the master cyl. down.

v8rman wrote:


I'm assuming from his post that his problem is at or near the master cylinder. The air can escape thru the bleeder or by moving into the mc reservoir and moving up to the top.
If it is near his mc it will be easier for it to move up into the resi as opposed to all the way down his line to the caliper and out thru the bleeder. If that makes any sense.

fmxrider wrote:


Normally the MC is allready above the caliper. Therefore you need to do the opposite, otherwise having the bike just sit in the garage as normal would do the same thing.

i bled it and no bubbles, so I simply took out the height adjuster and put it near the max, which raises the brake lever and it works just fine now. I think it wasnt pushing in all the way and that was my problem....

Thanks again for all the feedback!