Sorry if the answer is already out there, I cant seem to pinpoint the problem with the search engine,

here I go.

I have a 2000 CBR 929RR with steel braided front brake lines. when standing still, the brakes bite fine, I feel resistance in the lever and the front tire won't budge if I through my weight into it.

as soon as the bike starts to roll, loss of pressure, the lever moves without resistance to the handlebar, and no front braking pressure is applied. Once I stop again, I pump the brake 2 or 3 times and voila, braking is restored untilI roll again...

I have tried bleeding the brakes from the banjo bolt and from the caliper in both cases smooth streams of brake fluid flow out, no visible signs of air. the reservoir is full.

Does anyone have any ideas what might be causing this?

 

Sounds like you make have bent rotors, has the bike ever been in an accident or did you buy a used front wheel from someone?

 

things to check....

1. Calipers are tight and pads are properly seated in the caliper.
2. You used new copper sealing rings whenever you installed the lines?
3. Just because you have solid brake fluid doesnt mean all the air is out....

I just put on front stainless lines and even after the fluid was solid from the calipers i still had a soft lever. I kept going for another few minutes and more air started coming out. It took me about 25-30 minutes total to bleed all the air out of the lines.

4. Make sure the pads are totally worn down. If they are too far down and its steel on steel, the calipers could be overheating causing a soft lever.

 

BLEED,BLEED,BLEED! I just changed my fluid yesterday and went through over one full resivoir's worth before I got it good and bled thoroughly.
RB

 

I went through 3/4 of a quart of the expensive stuff when I changed my lines, alternating left and right bleeding. I'd do about 5 reseviors worth of fluid on one side, then start the other side, 5 more, then back to the first side.

 

Ok, so more bleeding? at the caliber level? or master?

and btw, yes the bike had been in an accident, I bought it from a guy who had dropped it on its left side at low speeds.

My question is: why would the pressure decrease to 0 once the wheel turns? because the pads back away from the disk?

 

yeah...my thought is if you have a firm lever....and it stays firm and ONLY softens after moving the bike...i would listen for scraping...sounds like the rotors might be bent or warped and as you push the bike or pushing the pads back into the caliper...then when you stop, you are pumping to get them back to the rotor...

but that is ASSUMING you bled correctly and have a firm lever and it ONLY softens when the bike is moved....

 

ffingers, that sounds exactly like what is happening. When I get pressure, I will keep the pressure for days while the bike sits in the garage, The brakes grip great, but when I start rolling the bike out of the garage, I do hear a bit of scraping and then nothing, and no more brakes.

How do I check the rotors for warping/bending? and do you think it is safe to assume that if it was dropped on the left side only the left rotor is bent?

And one last question, if I have seperate braided lines going to each caliper, wouldnt I get braking on one side at least?

 

alright, here's a few answers...assuming that this MIGHT be the problem..to check for it...

take off the front wheel, and check to make sure the rim is right....meaning you might have flat rotors, but they are mounting weird to the rim, meaning they are slanted, this could be due to a bent rim or just them being incorrectly mounted (i only say to check this because the bike went down)

if the rim is fine and the mounting is all fine, put the rotors on a flat surface on one side then the other...check to see if they are flat....you SHOULD be able to a warp or deformation if it's forcing all the pressure out of your lever....if it still looks flat, you can take it to any mechanic, they should be able to check the planar surface of the rotors to see if it's within tolerances....

finally, if you have SS lines, it's likely you have two lines going from the M/C...the same M/C feeds both lines, so considering the fluid will flow to the path of least resistance, if one line is "filled" and the other isn't, you won't get braking until both lines are "filled" and there is pressure in both lines...so it's very possible to have a fully functioning one caliper, but not get any braking because the other isn't under pressure....essentially both lines have to be under pressure for it to work correctly...(i don't know if i explained this well, but you get my drift?)

as for assuming that only the left is bent...i have no idea...i would check both just to be safe....i would hate to go through all the hassle of taking everything apart, checking one rotor only to find out that both are messed....

best of luck, let us know what you find..

 

I will try and take off the rotors tommorrow, how hard is it to remove the front wheel? anything really tricky? are there any DIYs or step by step?