brake bleeding

Random13 · Scooby Slapper Joined: 12 May 2013 Karma :

Hi All,

I have just rebuilt my calipers and drained the old fluid.

Once put it all back together and time for bleeding , I did feel the servo unit but when I placed the diaphgram back in at the end the level went all the way above maximum and some spilled out .

I think my bikes are ok but can see constant spill from the servo. I think it is due to been overfilled.

Does going above the max limit on brake fluid reduce braking capability because it has no where to pass the air or pressure when the pistons are returned after you let the brake handle go .
I am not sure even if my theory above is correct but certainly the overfill has impacted the brake .

I am going to remove the extra but thought it is worth asking for future reference .

Also do I have to squeeze the diaphgram after it is removed as it seems to have expended in size and is as tall as the low mark . what is its job anyway ? not let water and air in ?

serlant · Brolly Dolly Joined: 06 Jul 2009 Karma :

what is even going on here? the level of brake fluid in the master cylinder will have zero effect on the brakes? aslong as there is enough then there is enough. there should be a minimum line in the fluid window or on the container, fill it above this. it does not need filling right to the top. bleed the brakes. fill until the sight glass is full (i normally leave the smallest of air bubbles) then put the diaphragm/seal on. then close up master cyclinder.

my guess would be the diaphragm extends so that as the brake fluid level drops as the brake pads wear, a vacuum is not created in the master cylinder, I guess this would result in having to pump the brakes every time you used them.
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davebike · World Chat Champion Joined: 15 Nov 2013 Karma :

Servo Unit ?? is the a BMW with the "power Brakes!
AFASK BMW are the only bikes with Servos

If so need to bleed / change the fluid is both the cirkets on whichever brake you are working on the bike has 4 lots of fluid for the brakes
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Random13 · Scooby Slapper Joined: 12 May 2013 Karma :

thanks , I know it seemed very confusing .

[quote] a vacuum is not created in the master cylinder, I guess this would result in having to pump the brakes every time you used them.[/quote]

what do u mean by having to pump everytime you use them

Rogerborg · nimbA Joined: 26 Oct 2010 Karma :

I'm going to assume that you mean master cylinder and not servo.

Over-filling shouldn't have an effect on braking performance. I'm imagine that you've just got air in the system. It can be a sod to get out sometimes. Behind the pistons, lurking in the other pipe of a linked circuit, at the banjos. I'm a recent convert to reverse bleeding by pushing it in at the caliper with a syringe.

It would be helpful if you told us what bike this is.
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barrkel · World Chat Champion Joined: 30 Jul 2012 Karma :

Random13 · Scooby Slapper Joined: 12 May 2013 Karma :

@barrkel , it makes perfect sense many thank

@Rogerborg, you are right. I meant the reservoir rather than servo . What do you mea by revere bleeding , can you elaborate?

I did try to bleed mine for about 1 hour and all of it was clear fluid so decided to ride it and test it in few days again as maybe some air is up there and not deciding to pup down.