couchcommando Posted May 24, 2013 Report Share Posted May 24, 2013 Fitted hoses to my 2002 CBR600FS a while back, at the last trackday the brakes went spongy, since getting it home I've bled the brakes again and they feel fine but after a few minutes they are spongy and the lever needs pumping to get the pressure. I can't find any leaks and when bleeding there is no air coming out the fluid. Anything I'm missing or any ideas where the problem lies, thanks Link to comment Share on other sites More sharing options...
BudgetBoy Posted May 24, 2013 Report Share Posted May 24, 2013 Air in the master cylinder & or calipers still. And trust me,, you may think you have all the air out but it will open your eyes when you tilt the MC to one side and see air come out. And don't tie the lever back as it does **** all. Another thing that can cause those issues is bad seals on the pistons.They can swell with heat and dont do what they should. Link to comment Share on other sites More sharing options...
couchcommando Posted May 24, 2013 Author Report Share Posted May 24, 2013 So should I take the master cylinder off the bars and move it about a bit ? Link to comment Share on other sites More sharing options...
EvilSpike Posted May 24, 2013 Report Share Posted May 24, 2013 And don't tie the lever back as it does **** all. See I know this has been discussed to death before, but I'm still in the 'it does work camp'. The reason why is when dealing with bits of kit we shove off the side of the ship and drop down to 3000m (about 300 atmospheres) we see significant gas separation out of fluids. They are recovered very slowly so it's not a case of de-pressurising gas release, but what I think, and I'm often very wrong in what I think, is that: If you quadruple the pressure in the system, and gas bubble will halve is size. Smaller bubbles might be better able to work their way around kinks in the system, especially when subjected to high frequency vibration. Pressurise the system, smaller bubbles move up easier through the fluid possibly and end up either close to the reservoir in the master cylinder or near a bleed nipple. Just a guess, and I doubt that tying the lever back overnight is ever going to hurt... As for the OP Couch, have you thought about rebuilding the master cylinder. I bought one for my ZXR400 from wemoto and it was only a few quid. I haven't installed it yet but it could be the M/C piston is a bit worn and allowing gas in? Link to comment Share on other sites More sharing options...
BudgetBoy Posted May 24, 2013 Report Share Posted May 24, 2013 So should I take the master cylinder off the bars and move it about a bit ? yeah wont hurt IMO. I have done it in the past. I have also removed the calipers and tilted them a little more (with a bit of wood in where the disc would sit) and pump the lever with the bleed nipple open. Everyone has different ways.. I only do what i said if it is stubborn.. if after all that its still the same i do summat else, then if that fails i rebuild the calipers or MC. See I know this has been discussed to death before, but I'm still in the 'it does work camp'. Yeah i know,, its one of those thing init lol.. By i alway base mine on the way the MC has been built. Anyhow im not getting into it.. Everyone is different but i have NEVER found it to work myself.. Link to comment Share on other sites More sharing options...
CMSMJ1 Posted May 24, 2013 Report Share Posted May 24, 2013 I reckon it works too... Link to comment Share on other sites More sharing options...
timbrell Posted May 24, 2013 Report Share Posted May 24, 2013 Don't know where the banjo sits on the master cylinder but if it's the highest point try squeezing the lever and cracking the banjo. I was amazed how much air came out of there when I was having problems bleeding. You need a fairly large rag though because it's not as clean as using a bleed nipple! Rebuilding the master cylinder is cheap but I've found it to be 50/50 whether it works or not. Twice I've done that only to find the bore was knackered so it still didn't work. Could just be my infamous bad luck though. Link to comment Share on other sites More sharing options...
Mark/Foggy Posted May 25, 2013 Report Share Posted May 25, 2013 I'm a fan of working the last bit hot, i.e. proper working temp. Get a bungy around the lever and crack all the bleed nipples and banjo's off and back on, starting at the bottom. If this doesn't sort it, there's a problem somewhere, probably a seal leak. Link to comment Share on other sites More sharing options...
couchcommando Posted June 2, 2013 Author Report Share Posted June 2, 2013 Bit of an update here, finally bled the brakes and they felt fine, however they still needed pumping two or three times to get proper pressure, then when left for a few seconds they would need pumping again, I hadn't ridden the bike since it had new wheels and discs in so I took it for a spin, the discs were completely knackered and pulsed badly through the lever, once home I took them off and they are not flat but dished and warped, put my old discs on which I know to be straight and the brakes are perfect now,can only assume the discs were bending as the brakes were put on and once released were pushing the pistons back into the caliber s, can't think of any other answer but all sorted Link to comment Share on other sites More sharing options...
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