trevbul1 Posted May 21, 2015 Report Share Posted May 21, 2015 Hi. Just fitted new front pads to my Gas Gas 300. I had to push the (four) pistons as far back as they would go to get the new pads over the disc. But on re-assembly, the brake was spongy, so I bled it. Still spongy. So I bled it again using gravity to get the fluid through, and no, I didn't let the master cylinder empty... trouble is, I now have no brake pressure whatsoever and no amount of bleeding is bringing it back. Where should I go from here, please? Cheers for any help. Quote Link to comment Share on other sites More sharing options...
dadof2 Posted May 21, 2015 Report Share Posted May 21, 2015 "Where should I go from here please" - stick to level ground or gentle slopes Getting the pistons to move again after being pushed fully back is often a problem particularly on 4 pot callipers, all pumping the lever does is flex the seals back and forth. Check pads and clips / pins are in good order, free to move and not bent, If the pad, clip or pin is bent or binding it can act like a spring keep pushing a piston back. There could still be some air in your hose, Make sure your master cylinder piston is retracting fully. Park the bike up for a few hours or overnight with the master cylinder hung so there are no up loops that could trap air in your hose. The bleed by the following method, pull the lever back to the bars, then briefly crack the bleed nipple open and closed. Release the lever, wait a few seconds then repeat several times, checking to see if pistons are starting to move. Once you are sure all air is out pull lever back to bars and pour boiling water over calliper until it and fluid inside is hot. Re bleed keeping calliper hot. If that fails pressure bleed. If that fails a detail strip down is advised. 1 Quote Link to comment Share on other sites More sharing options...
steve_earle Posted May 21, 2015 Report Share Posted May 21, 2015 Make sure there is free play in the lever so the master cylinder can extend fully and draw fluid from the reservoir. If you have trouble bleeding then there is a problem with the caliper or M/C, I would guess the caliper following what you have done. Strip it down, clean and rebuild as Dadoff has suggested. Quote Link to comment Share on other sites More sharing options...
lineaway Posted May 22, 2015 Report Share Posted May 22, 2015 Use a clear hose that goes above the master cylinder. Quote Link to comment Share on other sites More sharing options...
crazybond700 Posted May 22, 2015 Report Share Posted May 22, 2015 (edited) There should not have air been able to get into the system though! So maybe messed up somewhere, but no worries, than you should be able to fix it again. Make sure lever has play enough, and bleed the system like mentioned above. What could help next time, take caliper off, hold 3 of the four pistons (with piece of wood or something and a clamp). And try if you can push 1 out a bit and do this step for the next pistons aswel. And then really tighly put the blocks in, and push the blocks in only as far as needed, and make it hard to get the caliper on. Making that step a bit more diffucult will make it less likely the situation you have occures Edited May 22, 2015 by crazybond700 Quote Link to comment Share on other sites More sharing options...
trevbul1 Posted May 23, 2015 Author Report Share Posted May 23, 2015 Big thanks to everyone who replied - gotta love forums / YouTube! In a combination of advice I canted the bars to get the m/cyl as high as possible, slacked off the lever and left overnight. Presto, some pressure back in the morning. Next I did indeed wedge/ clamp three pistons in place forcing the fourth sticky one to move. Reassambled and re-bled normally. Now all I have to do is wear the spilt brake fluid off the pads and disc.... Really big thanks again to everyone for taking the time and trouble to reply with such thought. Happy sunny Bank Holiday everyone. Quote Link to comment Share on other sites More sharing options...
zippy Posted May 24, 2015 Report Share Posted May 24, 2015 if you have spilled brake fluid all over the pads and disc, you may want to buy new pads. Pads will have a habit of absorbing the brake fluid. Disc can be spray cleaned with brake cleaner. Quote Link to comment Share on other sites More sharing options...
dadof2 Posted May 24, 2015 Report Share Posted May 24, 2015 Glad you got it sorted. Just thought I would mention something I came across on a clutch recently. Clutch was working OKish but not giving the bite point it should or had previously. All it needed was a change of fluid. Started to change the fluid then master cylinder piston would not return far enough to uncover fill port on return stroke after bleeding. The master cylinder spring had weakened slightly with age. When the return flow of fluid is assisted by clutch springs there was no problem, it only occurred after bleed stroke. This weak spring gave exactly same symptoms as you had on brakes. Quote Link to comment Share on other sites More sharing options...
crazybond700 Posted May 25, 2015 Report Share Posted May 25, 2015 (edited) Tywrapping the lever and leave it for a night often also can help btw (in case of not bleeding too well) Edited May 25, 2015 by crazybond700 Quote Link to comment Share on other sites More sharing options...
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