how to "un-air" rear brake?

mkavci9

mkavci9

Full member
Location
Slovenija
Hello, i have one question.

I changed sprockes, chain and clutch oil on my laverda 1200 MIrage. Before i monuted rear tye, i saw that something felt out of califer. Taht was 3cm ling stift, which hold the spring upper t he brake pads. I unscrewed the caliper apart and put all again on its place. i Was  keeping an eye on that oring in the middle which is sealing oil. All OK. But problem is, that when I wanted to "un-air" the caliper in standard way "few times push lever- hold- unscrew oil screw, screw it and repeat"  But no success. IS there some special way to do this? I had same problem with first master cilinder and clutch. I had to hold master cilinder in particular position, that air went out.

Thanks for answers.

martin
 
Hi Martin

I'm not sure why you disassembled the caliper to put the little spring pin back, but never mind, it's done now.

Rear brakes are sometimes hard to bleed because air bubbles will stay at the highest part of the brake hose. Pumping with the master cylinder doesn't move enough fluid to get the bubbles out. If you have no other bleeding equipment (like a vacuum bleeder) the easiest way to get the air out is to take the caliper off the wheel and put it somewhere (like on a box or chair) so that the bleed screw becomes the highest point in the system. You should then be able to pump the air through with the master cylinder. Tapping on the hose with a screwdriver will help shake any small bubbles loose so they will float up to the bleed screw. Don't forget to put something about the same thickness of the disk between the pads to stop them moving too far out. A piece of 6mm plywood should do.

Cam
 
I disasseasembled the caliper, because I suspected that this stift fall from caliper. but I wasn't sure from where. ANd only after that i went to green book to be sure where is spring possitionated. So as I understand, again wheel down, and make this on your advice DEllortoman. Thanks.

Laverda is realy economic bike. Last weekend I enjoyed to service her, this weekend again:) No riding:) Pure joy, for free.
 
HEllo,
i will use this old post, that I wrote.  I have problem s with rear brake again. Again, after winter, my brake have air inside. There is no leaking anywhere.  I tried to "un-air" the system vith  vacum tool, to drain ht ol, but no success. Sems that this tool is to weak, to vacum the oil trough the system.
I changed the brembo seals kit in the main cylinder couple of years ago. Every start of the season the brake was down, with air, but every time I succeded to get rid of the air, if friend helped me to hold the bike in a way, that rear tyre was much higher than front tyre.  Somebody here told me tht in this way you get rid of air in the hose. But This year this dont work any more.
I can try to take calipers down and hold them higher than oil pump, but I think that this time is something different. Actually after some time-repetitions of geting rid of the air, i can manage to obtain the hard pedal. But, than after 10 second again pedal  goes till the end.. so no braking.

Is possible that some thigs is blocked? aome dirt in the oil?  in the empty reservior you can see two small holes for the oil. Did somebody experienced blocked holes?
Strange..

Thanks for any advice,
by
 
hello. i still have a problem with rear brake. "luckily" i dont have time to ride my bike.
Anyway I have to fix this. 
I took the caliper and master cylinder from the bike and tried to "get rid of air" in the system.  I fixed caliper in bench vise on the table. the bleed nipple on caliper is on top, the brake hose is almost vertical, and manualy pumped lever onaster cylinder. I can get rid of the air in the system but i cant get hard lever-pedal.
before this, I also dismantled and cleaned the master cylinder which had a bit of greasy dirt inside. small holes in reservioar are clean. i changed the brembo p15 piston kit few years ago so it should be ok?? or?  seals looks ok. I use some Dot4 oil. should I use some special dot4 oil? 
is possible that is problem inside calipers? but i guess that if there is no leaking is all ok. they were renewd alrrady. 
any clue?
thanks. Martin
 
Try:
? Holding the caliper in a position so the bleed is at the top.
? Push the master cylinder half way (to close it against push-back of fluid). Hold it there.
? Push the caliper pistons in, to eject air through the bleed nipples. Push them all the way in until they stop.
? Tighten bleed nipples.
? Release master cylinder.
? Pump the master cylinder to get caliper pistons back to a normal position.
? Repeat if required.

HTH, Paul H
 
An alternative method, which I find more effective, after checking the fluid level is good, replace cap and unbolt the master cylinder. Hold it above the stretched hose and pump the lever slowly a couple of times until you feel it firm up.
 
https://www.ebay.co.uk/itm/Mityvac-MV8510-Silverline-Elite-Metal-Hand-Pump/310209933940?epid=1747158715&hash=item4839f3f274:g:WmAAAMXQiNdRcT5I
 
thanks for answers, I have a vacum pump that works on cars good and so on. BUt here on laverda it keeps sucking air but it dont came to pure oil. Just suckings bubles. I dont know if  the air go by - under the bleed nipple. It is vacuming, bu looks that is not enough strong, or I don't know something.

I will try Haggis advice, and lets see.  HEre in Slovenia, is one company that is producing al king of seals. For escavators-pistons,powerhammers,  for engines, orings, x-rings, kinda everything. They said to me, that  I have to bring a piston and cylinder to them, and they will make  replicas. Will maybe try. Anybody tried already?


thanks
 
They are famous for being a bit tricky - many posts on here from frustrated owners - like you, no doubt!! Try Haggis's idea - a few people have mentioned having success with this, which is kind of the reverse of what you'd think was correct ... but if it works, who cares?!  :D

Good luck. And don't forget - ride your bike!!
 
When I had difficulties to evavuate my rear brake after butting all items in one direction, brake calipers up on highest point and it did not work, finally the master cylinder was the problem. It stucked an did not go back completely.
After a dismantling it and arranged free movement of the piston evacuating was easy. Good luck.
Andre
 
I'm chuffed it worked for you Martin.

There is no right or wrong way. I find it just helps visualising the air bubble and where it wants to be, and then finding a cunning plan to move it out to meet its buddies in the atmosphere.

The trick of applying reverse pressure/flow via the slave cyl (in this case, caliper) was learnt the hard way, 30 years ago, flat on my back under MGBs, which have a high loop in the clutch pipe circuit. Happy days. Much rust in the eye.

Great news. Now ride the tits of her, if you can. Hag.

 
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