front brake master cylinder testing

[Anonymous]

or you could just use a big fecking anchor

[Anonymous]

just wondered if there’s an easy way ??
rather than change the front brake master cylinder and spend forever and a day bleeding it , to see if it’s any good …
is there any way of doing a pressure test prior to fitting ??
?

[Laudanum]

stick a hose on it and clamp it to a set of bar in a vice, raise the open end of the hose so its above the level of the master cylinder, pump it slowly until all the air is out.
Now the fun part,pinch the banjo with your thumb and finger as hard as you can and slowly pump again, if its any good fluid should easily force its way out, don’t wear your best jeans, keep it away from your face and anything else you don’t want covered in brake fluid.

[dougyt]

OK, you’re relying on this cylinder to stop you and the bike, instead of using a stationary object to slow you down when you hit it. I would take the slightly longer winded method of strip down and check it before fitting, and maybe just resealing it as a precaution.
Where brakes are concerned cutting corners is not a good idea.

Having said that, Laudanums method will work, and you don’t even need the hose, just put your finger over the hole where the hose goes in, pull the lever back, and you will feel the pressure but you shouldn’t be able to prevent it from getting out past your finger. Wearing gloves is also a good idea as brake fluid is a nasty substance for sensitive skin. Make sure to avoid getting brake fluid on paintwork, as it makes very good paint stripper.

[Anonymous]

thanks folks !
that’s most helpful ,
should there be any difference in the pressure if you ran twin disks ??
?

[dougyt]

The pressure is not the important factor, it’s the volume of fluid moved. At its simplest terms, With an extra calliper to move you will need a master cylinder which will move more fluid or your lever is going to move a long way to move the callipers enought to apply the pads.
In a more technical answer, you will need to know the size of the pistons in the callipers, and the size of the piston in the master cylinder to work out a ratio.
Here is a site with a little in depth detail about brake ratios http://www.vintagebrake.com/mastercylinder.htm

[Laudanum]

Strange things master cylinders, they can work fine and pack up when you change brake pads etc, I assume there is a small amount of pressure left that pushes against the seal but when it is released the seal fails.
Probably why the cure for spongy brakes is to pump it until you get a lever then cable tie it to the bars overnight.

[speedy]

💡 one little tip is when changing your brake pads instaed of forcing the pistons back and pushing the fluid back into the master cylinder undo the bleed nipple first then push the pistons back then tighten the bleed nipple back up while holding the pistons back

then refit your new pads pump the pistons out and top up your fluid level a small amount of bleeding maybe required but the risk of twisting the master cylider rubbers is reduced and your putting fresh brake fluid in which on most bikes should be done as periodic maintainance every two to three years anyway

[Author]

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