lian Posted February 5, 2014 Report Share Posted February 5, 2014 Hi everyone. I noticed my front brake became plush, so decided to bleed it, but after some time of process i found that brake fluid is appearing on the exterior of piston (marked at the picture). I thought it is due to the marked seal has worn out, but decided to bleed to the end... The end was not so lucky so i bought new kit from splatshop and installed it. But to my disappointment the fluid leak is appeared at the same place and bleeding the brakes is impossible - i pumped lever long time and already have no bubbles out of caliper, but lever is plush and a bit of fluid present at the exterior of piston again. Some time tiny bubbles comes out of 2 little holes in the master cylinder, i assume it is because of that leakage air comes in. What do you think caused this? Rebuild kit couldn't be defective..so it must work fine but no PS. one thought - since seal is not blocking fluid and let air in, maybe put some thin layer of something under it to enlarge seal's radius and it will densely pack an inner tube in MC? Could this solve a problem? Quote Link to comment Share on other sites More sharing options...
lineaway Posted February 5, 2014 Report Share Posted February 5, 2014 You actually need to look inside the bore and see if it is scratched. Quote Link to comment Share on other sites More sharing options...
lewis cosgrove Posted February 5, 2014 Report Share Posted February 5, 2014 9niggas? The guy from youtube? Quote Link to comment Share on other sites More sharing options...
lian Posted February 5, 2014 Author Report Share Posted February 5, 2014 The bore is not scratched, and leakage started even before i start to disassemble and inspect the problem. Could be that old seal rubbed a bigger bore inside mc and therefore new one can't fill it and leaking? Lewis, yes, how did u know? Quote Link to comment Share on other sites More sharing options...
lewis cosgrove Posted February 5, 2014 Report Share Posted February 5, 2014 The hair (no homo) Make sure the bore is clean and smooth. Might seem pointless but try remove that brown/orange stuff from the rim of the bore and under the circlip, you dont want dirt messing with the oring. Looking at the pictures above there looks to be alot of gunk! Quote Link to comment Share on other sites More sharing options...
guys Posted February 5, 2014 Report Share Posted February 5, 2014 (edited) If a master cylinder still leaks with a new seal kit either the bore is scratched, worn or contaminated/dirty Edited February 5, 2014 by guys Quote Link to comment Share on other sites More sharing options...
lian Posted February 5, 2014 Author Report Share Posted February 5, 2014 (edited) I removed that brown dirt just in case, bore looking smooth and clean inside. Maybe i should clean it with a piece of cloth, but i didn't. Didn't seen dirt inside also. Have tried wind the thread on a piston under that seal, to increase its diameter, piston got inside the bore harder and stuck, but when i greased seal with brake fluid, it started to move freely inside, so i could pump it by lever and watch for a leak. It is still leaking.. Maybe i wind too little of the threads and seal is still not fills the bore completely? If there is scratches (from what??), they should be really impressive to cause leakage or even if they are tiny little lines they will do that? Can someone inspect their levers to see is there a bit of fluid or not? Edited February 5, 2014 by lian Quote Link to comment Share on other sites More sharing options...
lian Posted February 5, 2014 Author Report Share Posted February 5, 2014 By the way, that seal i have marked on a picture - is it actually seal or dust seal to prevent getting dirt inside? Which from they two is pushing the liquid and stops it from getting to outside? And when lever released, first seal (like skirt) is in front of 2 little holes in cylinder with Dot4, or overlaps one of them? Quote Link to comment Share on other sites More sharing options...
lian Posted March 25, 2014 Author Report Share Posted March 25, 2014 UPDATE: Problem with seal on MC, i have ignored, air do not enter in hydro-line, only some bubbles are getting in MC through 2 holes. Another problem/question. Have bought new AJP caliper, because in old one seals on pistons didn't take pressure, even with new seals. Idk why.. So, 1. Inverse bleed it, carefully, 3 of 20ml syringes with "pulse technique", after that bleed it in usual way, from up to down - 1 m.cylinder of fluid. Lever got good feeling, almost no spongy feeling, no air out from plastic tube but... But after i release lever, i can't turn wheel - it stuck like i'm pushing brake lever half-way. Bleed one more cylinder, but this problem left, wheel don't turn free. What does it mean, why pistons do not return? 2. Disassembled caliper and assemble it again, inverse bleed the same way, but now lever is too spongy and even can't get pressure after few m/c bleed from up to down. No air out from tube on a caliper bolt, this is strange, and no pressure too... And i noticed that brake fluid is seen under the 2 pistons, when im pulling lever, pistons get out a bit and around them is a little bit of a fluid, too little. I don't know, maybe it drop there when i inverse bleed it, because some of it was leaking out from bolt, when i pushed from syringe, but i wiped it always with towel. If fluid didn't drop from bolt, could it be that it leaking from under pistons and therefore my lever became flabby and i can't get pressure? Could it be something with new caliper - seals on pistons? (i pushed pistons full back to caliper's body when disassembled it in 2 halves, but i beleive i couldn't damage seals somehow by doing that, just pushed it back.. it was not too easy, they went hard). Quote Link to comment Share on other sites More sharing options...
lineaway Posted March 25, 2014 Report Share Posted March 25, 2014 When the wheel was locked, did you have free play on the piston at the M/C? That piston has too move all the way back to release. Quote Link to comment Share on other sites More sharing options...
lian Posted March 26, 2014 Author Report Share Posted March 26, 2014 Yes, it was free play. Quote Link to comment Share on other sites More sharing options...
lian Posted March 31, 2014 Author Report Share Posted March 31, 2014 (edited) http://youtu.be/ejyOVDjZCz4 1. You can see it on video, maybe give me some suggestions after? 2. Pads do not return back - does it mean air is inside and pads was pushed but after releasing lever, air is enlarged and pads just don't move because there was not back force of fluid (or something like that...) Sound on video is shifted somehow, more info under video frame on youtube. Edited March 31, 2014 by lian Quote Link to comment Share on other sites More sharing options...
lineaway Posted April 1, 2014 Report Share Posted April 1, 2014 Still looks like not enough free play. You are not trying to adjust it for when you are riding. How did you bleed the brakes? I would get a piece of long clear hose (3 feet) to bleed from the caliper. Run the hose up over one of your grips to make the fluid and air push up. You might even remove the lever and use a phillips screw driver to pump the M/C. Good luck. Quote Link to comment Share on other sites More sharing options...
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