Master cylinder rebuilds

twhiteman42

New Member
Having trouble, old one leaked so done rebuild and can't get to pump up. Yes I tried line off pumping and pumping fluid through bleeder and dosen't seem like a fluid issue, more like a cylinder problem. Do I need to hone it and where do I get a hone this small. it is only 5/8" bore ???? any comments welcome. Been fightin it for 2 days now :(
 

jsub

Active Member
I was ready to throw in the towel on my front brake cylinder & as a last resort I pressed the front pistons all the way in & started over. It pressured up right away.
 

Raywood

The Pirate
Staff member
Calendar Participant
Troop Supporter
Having trouble, old one leaked so done rebuild and can't get to pump up. Yes I tried line off pumping and pumping fluid through bleeder and dosen't seem like a fluid issue, more like a cylinder problem. Do I need to hone it and where do I get a hone this small. it is only 5/8" bore ???? any comments welcome. Been fightin it for 2 days now :(
Did you do the full rebuild with the whole kit? Lots of little parts in there. If so I would pull it back apart and ensure you put everything back together following the instructions.

Might try a vac brake bleeder. You can get a cheap one at Sears for a few bucks.

:cheers:
 

goliath

Member
I had the same problem - put in the rebuild kit - nothing. I wanted to make sure it wasn't my caliper so I took my foot brake off and hooked the front to that just to make sure it was working. Once I knew it was working I took the caliper end of the hose and stuck it in the brake fluid bottle and kept pumping the handle and adding brake fluid until I saw no more bubbles in the bottle. Then losing as little fluid as possible I connected the hose. Unfortunately I had to pump the handle into the throttle several hundred times and eventually I started to get pedal but it did take a crazy amount of time. Also I had one other problem - one of my copper washers had a tiny nick in it and was allowing air to suck back through so do yourself a favor and replace the washers - they're cheap. Also, make sure the banjo bolts are real tight so no air gets back through. Hope this helps because this made me crazy for a while.
Bill
 

mobsta

Well-Known Member
take a oil can,fill with fluid,hook a hose to it.then hook other end to the caliper bleed screw.open bleed screw slightly and pump oil can so fluid runs up to master cylinder.master should be at least half full when starting this.works for me. just sayin:cheers:
 

Moespeeds

Well-Known Member
Don't ever run a hone through there. If you can't get it bled using the above suggestions, take it all apart, clean it all out, put some caliper grease on the o-rings, and try again. When you flick the lever, are you getting bubbles up at the reservoir? Also listen for any sucking or squishing sounds coming from the Master cylinder, if you hear that and you continuously get bubbles, you are probably sucking air somewhere. Try tapping the lines, turning the forks back and forth if it's the front, etc. Anything to knock bubbles loose. Crack the banjo bolts individually with the lever pulled as if you are cracking the bleeder bolt, sometimes air can get trapped there. Also, change out those washers for the HD type with the rubber seal on them. You can get them at any dealer, just bring an old washer to verify the size. If your piston has the little rubber piece at one end, make sure you have it going the right direction. It looks like it should go on there like a hat, but really it needs to sit up there like a cup, with the open end facing away from the piston.
 

twhiteman42

New Member
WOW, Lot's of great info and I did finally get it by using Mobsta's trick :) everyone else was great too EXCEPT FOR IAN !!!! I don't take anything to a bike shop, with a little effort there is nothing we can't fix. Sometimes it gets a little stubborn but we get through it and I aint payin NOBODY to work on my bike :) Thanks to ALL, (except IAN lol )
 

MARV

Well-Known Member
Yes I tried line off pumping and pumping fluid through bleeder and dosen't seem like a fluid issue, more like a cylinder problem. :(
take a oil can,fill with fluid,hook a hose to it.then hook other end to the caliper bleed screw.open bleed screw slightly and pump oil can so fluid runs up to master cylinder.master should be at least half full when starting this.works for me. just sayin:cheers:
I did finally get it by using Mobsta's trick :)
how come it didnt work the first time you pumped through the bleeder?
 

twhiteman42

New Member
1st time i wasn't using an oil pump type can, i was just squeezing a crappy bottle I made up. Nice of you to keep track though Marv, MOBSTA RULES !!!!
 
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