Brake lever loses pressure (bleeding brakes)

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 until I 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

quote:

ORIGINAL: FNQuickF2

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?

You shouldn't have to use that much fluid to bleed the brakes.  You guys are probably doing it wrong, letting air go back into the lines (meaning you have to keep doing it).

Don't open the valve too wide, and don't let it stay open too long, and don't let the resevoir go dry.

to remove the wheel...just loosen the two pinch bolts on either fork...unscrew the axle nut...slide out the axle and the wheel will drop down...only thing you have to worry about is that there are spacers on either side...having different widths...i believe the wider one goes on the right (i am thinking from memory here)....
 
there's a nice tutorial here... How to remove/install front wheel!

Also, my Clymers manual says to make the tube you use loop above the valve to make sure no air gets back into the caliper.

Well well well, I took it into the dealer, cause I don't like messing around with the brakes with limited knowledge, and both my disks are bent, I have leaking forks, and I need a new horn !!?%&!~
 
Do any of you knowledgable people out there know if there is an inexpensive way around buying 2 new rotors? I am looking to find used ones, but they seem to be hard to come by. Do rotors from any other honda products fit? F4i? can they be remachined? corrected?
 
2nd and 3rd, how much does it cost you guys to have your fork seals changed? they are charging me like 200$ and I need a horn! anybody got one? (200 CBR 929RR)?
 
thanks in advance for the help

wow...today might be your lucky day....i MIGHT be...(like 90% sure) be buying a set of galfer wave rotors for my bike and will be getting rid of my OEM ones...i was going to throw them up on ebay but if you want them, we can work something out (don't worry i am not going to screw you...lol)....they have about 6k on them MAYBE....they are in great condition, i just wanted an upgrade....

huh...i was right...whadda ya know...coolio!! sorry it meant bent rotors...

PM me about the rotors...

i got the stock horn from my 95 CBR, probably the same. I'll take a look later and see how different they are. If it will work, I'll send it to you for the cost of shipping, rounded up to the nearest dollar. I'm out of town till probably this weekend, so it would be a short wait.

Thats funny I just got a 2002 F4I last weekend and it has the same exact problem. Tried bleeding quite a bit, but rotors are insanely warped from a crash. Now I am considering what rotors to get. Does anyone have experience with these Chinese ones: http://cgi.ebay.com/ebaymotors/Front-Brake-Disc-Rotor-Honda-CBR-600-F4i-600RR-1000RR-G_W0QQitemZ200218755745QQcmdZViewItem ?