Bleeding the rear break until your hands hurt

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Ciobulus

Joined Jun 2007

30 Posts | 0+

Discussion Starter
• Apr 16, 2011

• #1

I started bleeding my break today.

I got a rubber tube, unscrewed the bleeder and connected everything like in the picture.

Started pumping the break and a lot of air bubbles started coming up the tube.

After a half an hour of pumping tiny bubbles were still coming out. I kept at it for an hour straight. My hands were killing me at this point. Finally the tiny air bubbles were gone.

I was pumping pure fluid without having to refill the reservoir.

Maybe the people having trouble with the rear break bleeding are just not trying hard enough because the tiny air bubbles wont get out of the lines even after 30 minutes of pumping the break directly in the reservoir.

I'l post a follow up on this procedure to let you guys know how long it kept firm.

 

Arryace

Joined Apr 2011

115 Posts | 0+

Bristol

• Apr 16, 2011

• #2

just a few thoughts:thumbup

be very careful re-using brakefluid especialy brake fluid with little bubbles in as those little bubbles get carried into the braking system and when the fluid is compressed they are forced together to make big bubbles and the problem starts all over again.

the simple solution is to remove the caliper from the bike (don't disconnect the brake line) and turn it upside down so the nipple is at the top as the air bubbles will all ways rise to the top this is why all that pumping is still producing bubbles and blled it this way up (need to put something between the pads).

better still bleed it as above when you have some pressure lock the rear brake lever down and leave over night, again forcing all those little bubbles to join togethter into bigger ones making them easier to get rid of.

i think that makes sense:thumbup

 

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Ciobulus

Joined Jun 2007

30 Posts | 0+

Discussion Starter
• Apr 16, 2011

• #3

The tiny air bubbles were big bubbles by the time they reached the reservoir so the reused fluid that went back into the tank was without bubbles. I get the need to have the caliper above everything but the breaks on your car are much lower and bleeding still works.

I've read somewhere on a aprilia forum where they dyno tested and heat tested the rear break system for RSV's and they came to the conclusion that the rear break master cylinder is bolted to the engine and that high freq vibrations cause tiny bubbles to form in the tubes. These bubbles are so tiny that the viscosity of the fluid wont let them move up. So getting them out with the fluid is the only way to remove them.

 

Arryace

Joined Apr 2011

115 Posts | 0+

Bristol

• Apr 16, 2011

• #4

ah right i see.
yes having them above the reservoir would help but is not necessary but having the bleed nipple at the top of the calliper will help you get rid of the air much quicker:thumbup

 

RussRSV

Joined Oct 2010

74 Posts | 0+

• Apr 16, 2011

• #5

Mate, the only way to bleed the rear brake is to take the rear caliper off and position it as high as possible with the nipple at the highest piont. This allows all the air to come out of the system.

The other thing is the position of the rear brake cylinder, the heat from the exhaust ruins the fluid and the brake will fail again. The way to solve this is to reposition the cylinder. Griff rear sets allow you to do this.

 

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genman

Joined Mar 2011

79 Posts | 0+

Belfast UK

• Apr 17, 2011

• #6

+1 on removing and elevating the rear caliper...push the pads / pistons fully into the caliper and place a bit of wood or similar between them.
Never ever put the pumped out fluid back into the system...clean or otherwise it will have tiny bubbles in it. Fresh fluid needs to sit for a week or so before use.
If repositioning the master cylinder aint a possibility then try a later 07 onward heatsheild plate,,,just bolts behind the master to absorb some of the heat...doesn't work around town though as the air isn't moving past to remove the heat build up....overall though it delays the frequency of bleeding.
I've tried larger master cylinders and calipers but it makes no difference until you can remove the cause of the bubbles.....HEAT boiling the fluid.

 

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Ciobulus

Joined Jun 2007

30 Posts | 0+

Discussion Starter
• Apr 17, 2011

• #7

I have read that real tests were performed to check if the master cylinder gets anywhere near the boiling point. They had heat sensors placed on the break lines in key spots to see if maybe only one spot gets hot enough. So its not the heat that's causing this. I can point you to the article on your e-mail maybe. After a long ride without using the break try to see if your lines and fluid are hot. This is the best way to test if heat is getting in the fluid heating it up to the boiling point Dot4 = 450 Celsius if I'm not mistaking. Or pump a bit out of the rear break bleeder.

 

Last edited: Apr 17, 2011

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genman

Joined Mar 2011

79 Posts | 0+

Belfast UK

• Apr 17, 2011

• #8

Its not the fluid itself that boiling....brake fluid is hydroscopic so after a few months has absorbed a small % of water from the air...its this water thats boiling and causing bubbles...tests with sensors will never show this without a datalogger running for months and continuous fluid tests to monitor the % water.

 

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Ciobulus

Joined Jun 2007

30 Posts | 0+

Discussion Starter
• Apr 17, 2011

• #9

New break fluid should have 0% water and absorb it over a long period of time (1 year) It takes up more water when you open the cap of the reservoir than in a whole month. So people should have firm pedals until the water gets boiled. It doesn't add up, people have the same issue after two weeks.

 

Arryace

Joined Apr 2011

115 Posts | 0+

Bristol

• Apr 18, 2011

• #10

but if you didn't bleed it fully you may get a rear brake and still have small air bubbles and over a couple of weeks small bubbles will join to make big ones and collect somewhere causing the brake to fail.

 

voledangler

Joined Mar 2011

24 Posts | 0+

Bucks

• Apr 18, 2011

• #11

I remember having to do this on my ZX9R, it took f*&^ing ages and I eventually worked out it was because of the non-return valve in the bleeder kit requiring a hell of a lot of pressure to overcome it. The air would just compress, rather than get pumped through into the little jar I was using to collect the waste fluid. The solution was to remove the non-return valve. If you prime the waste jar with some clean fluid and make sure that the end of the bleed tube remains immersed, then it should be easier to pump out the air.

 

mad biff

Joined Apr 2011

454 Posts | 0+

scotland

• Apr 21, 2011

• #12

hi guys lots of ways to bleed clutches and brakes , yous guys not heard of back bleeding ? i bleed clutches this way most of the time single piped systems or even muti piped braking systems it works a treat on most .so tools req= 1 decent sized old style oil can like grampa used on his old austin
2= one short piece of rubber tube to fit on oil can and nipple .3= syringe (big) .ok ready to start 1= suck all fluid from bowl 2=connect rubber tube to bleed nipple 3= open nipple and start pumping your thumb keep steady slow`ish rythem till bowl is full as it reaches max level while still pumping lock nipple .job done bobs yer uncle