dan williams Posted June 17, 2017 Report Share Posted June 17, 2017 Not asking for anything but just venting. Stuck rear caliper, rebuilt. Can't get rear brakes to bleed properly so disassemble master cylinder and chase bubbles and install rebuild kit in master cylinder. Bleed by disassembling master cylinder worked but new piston in master cylinder stuck. Remove piston and polish inside of master cylinder with Dremel and polishing compound. Clean and refit piston and attempt to bleed regular way. No luck. Who designed this system? Stared at bike for good half hour and figured obvious place for bubbles is top of master cylinder. If the banjo bolt has any space above hose holes it'll never properly bleed. So I ordered some titanium banjo bolts with bleeders on top. I'll try screwing one of those bad boys into the top of the master cylinder brake line mount and try bleeding it from the high point in the system. Let's see if that works. Quote Link to comment Share on other sites More sharing options...
lineaway Posted June 17, 2017 Report Share Posted June 17, 2017 Why not just crack it loose and retighten? A long clear hose draped all the way over the rear fender does wonders. Quote Link to comment Share on other sites More sharing options...
dan williams Posted June 17, 2017 Author Report Share Posted June 17, 2017 Did that. I suspect there is still space on top of the banjo bolt for air to hide in. Already ordered Ti goodies so..... You know I can't just let it go if I think I can fix it. 1 Quote Link to comment Share on other sites More sharing options...
technowaldo Posted June 17, 2017 Report Share Posted June 17, 2017 Just bite the bullet and buy a complete new master cylinder 90% of brake faults stem from the m c 1 Quote Link to comment Share on other sites More sharing options...
guy53 Posted June 17, 2017 Report Share Posted June 17, 2017 There is a kind of vacuum that suck the brake fluid from the '' thank '' through the bleeder, maybe that could help. Guy Quote Link to comment Share on other sites More sharing options...
trialstaz Posted June 17, 2017 Report Share Posted June 17, 2017 (edited) Can be tricky but following has always worked on Evo for me: Make sure rear slave cylinder pistons fully in (I take pads out and put a piece on wood in to hold pistons in), take master cylinder cap off. Get a decent size syringe and small length of clear pipe - prime syringe/pipe with fluid - then fit on caliper nipple. Crack the nipple open and carefully compress the syringe - fluid will rise in the tiny master cylinder reservoir - if bubbles then keep pumping (use another syringe to drain excess in master cylinder). Keep pressure on rear syringe and Pump the brake pedal - if no resistance then normally air trapped in the banjo on top of master cylinder - keep pressure on rear syringe, crack the banjo slightly and push pedal down. Keep pedal down and nip banjo and rear nipple - you should then start to get a pedal - sometimes need to repeat one or 2 times. Refit M/cyl cap and carefully wash any brake fluid and refit pads etc. if master cylinder seal leaking you will get small bubbles in reservoir when pumping it. Agree if master cylinder bore scored etc then replace unit. Edited June 17, 2017 by trialstaz Quote Link to comment Share on other sites More sharing options...
dan williams Posted June 17, 2017 Author Report Share Posted June 17, 2017 I retried cracking the hose connection at the top of the master cylinder and it pushed out air and pedal firmed up. I'll still put the bleeder on when it arrives. I did notice the clutch slave cylinder bleeder is the same style. Rear pads are screaming and not biting so I probably contaminated them. Easy to replace. Not a fan of the full metallic pads anyway. A bit too abrupt for my style (or lack of). Besides the rear brake it's been a good day to sort a few front end maintenance issues, replace the chain etc. I could buy a new bike but this one just feels so good I can't justify it. Quote Link to comment Share on other sites More sharing options...
dadof2 Posted June 17, 2017 Report Share Posted June 17, 2017 After trying various bleeding methods for clutch and brakes I have now concluded that pressure bleeding is the best option. All you need is a spare master cylinder cap with a small hole in it to which you can apply compressed air, I found 30 PSI has always been sufficient. Often after rebuilding a cylinder the amount of fluid moved by the pistons normal stroke only causes the seal to flex, it does not move the slave piston forward. When you release the lever the piston moves back to its original position as the seal "unflexes". No matter how many times you bleed the piston just rocks back and forth. Pressure bleeding reliably overcomes this. Quote Link to comment Share on other sites More sharing options...
dan williams Posted June 18, 2017 Author Report Share Posted June 18, 2017 Yup thought of that too but I figured that has a lot to do with air in the system absorbing some of the travel of a fully pressurized/purged system. When all the air is purged the system should have sufficient displacement to move the pucks past the elastic flex of the seals so they return to a new rest position. Once I got the last bit of air (assumed) burped the pads set up properly. I'm just not keen on using the regular banjo bolt as a purge point but it is the highest point on the system. it's all good now. At least until I fall off again 1 Quote Link to comment Share on other sites More sharing options...
dan williams Posted June 20, 2017 Author Report Share Posted June 20, 2017 Ok that ain't gonna work. Airbox gets in the way. Quote Link to comment Share on other sites More sharing options...
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