bleeding brakes help

[seancb]

hi all
does any body now the best way to bleed twin disc brakes the bike is 1979 r100/7 because it not bleeding right Sean

 

[John Armstrong]

While I'm no expert on brake bleeding,those who are may need a little more information than "it's not bleeding right".

Like "fluid is ok in the master cylinder, but won't come out of the bleed nipple when I crack it open and apply the front brake"

 

[seancb]

the brake master cylinder has been rebuilt has new pipes and fuid but when i pump the brake nothing comes out the bleed nipples Sean

 

[cookie]

stick a bit of clear hose on one of the bleed nipples on one caliper, put the other end in a jam jar.

open the nipple 1/4 turn at the same time as squeezing the lever. as it reaches the end of the lever travel, shut the nipple.

repeat as necessary. this could take a while

when fluid is clear of bubbles, move on to the other caliper.

if it doesn't work, there is another problem, or you need some kind of power bleeder to do the donkey work for you.
the trouble with many bike brake hydraulics, is that the master cylinder simply doesn't shift enough fluid in one stroke. sucking the fluid through with a mityvac or blowing it through from the master cylinder gets over that problem.

i suppose you've got one of those daft remote master cylinders under the tank to further complicate the issue?

 

[John Armstrong]

When I worked on gliders and light aircraft one trick was to back bleed by pushing fluid up from the caliper to the master cylinder with an oil can. Worked well and easily IIRC as less coordination needed.

 

[seancb]

will try that and let you now Sean

 

[millard]

When I worked on gliders and light aircraft one trick was to back bleed by pushing fluid up from the caliper to the master cylinder with an oil can. Worked well and easily IIRC as less coordination needed.

This works very well indeed, particularly if you've striped the caliper for a rebuild and are starting afresh. I use a large syringe with appropriate sized plastic tube attached, and pump the fluid from the caliper upwards.

If, in spite of your best efforts, your lever remains spongey, then pump the lever until it's hard then tie it back to the grip with a cable tie or something similar and leave it overnight. Give the calipers and lines a tap from time to time to encourage the air bubles to rise up to the master cylinder.

 

[John Roberts]

Are they Brembos? The way I bleed mine (R100RS, could well be the same) when they are being difficult is to have the nipple open just an eighth of a turn, put my finger on the hole and wrap a cloth around my hand to soak up the fluid, then pump away, keeping my finger on the hole to let the air out when I squeeze the lever but stop it going back in when I release it. Notice that I do NOT tighten the nipple inbetween strokes. I keep an eye on the level of the fluid in the reservoir in case it falls low enough to draw more air in. You can feel the air bubbling out with your fingertip, when the fluid comes out with no air you are nearly there. Tighten the nipple and repeat for the other caliper(?)

You can check if there is any air in the fluid by using the clear plastic tube and jar as cookie said. It seems to be a very quick way if all else fails.

And mind not to get any fluid on your paintwork unless you are using Dot 4. Having said that, if I wipe the clipers clean straight away it doesn't seem to damage the paint on them. If all goes well there shouldn't be too much fluid in the cloth. I expect there are good Health & Safety issues against doing it like that, though, so don't do as I do, natch.

PS I don't suppose it really matters which calipers you have, the principle will be the same.

 

[cookie]

Are they Brembos? The way I bleed mine (R100RS, could well be the same) when they are being difficult is to have the nipple open just an eighth of a turn, put my finger on the hole and wrap a cloth around my hand to soak up the fluid, then pump away, keeping my finger on the hole to let the air out when I squeeze the lever but stop it going back in when I release it. Notice that I do NOT tighten the nipple inbetween strokes. I keep an eye on the level of the fluid in the reservoir in case it falls low enough to draw more air in. You can feel the air bubbling out with your fingertip, when the fluid comes out with no air you are nearly there. Tighten the nipple and repeat for the other caliper(?)

You can check if there is any air in the fluid by using the clear plastic tube and jar as cookie said. It seems to be a very quick way if all else fails.

And mind not to get any fluid on your paintwork unless you are using Dot 4. Having said that, if I wipe the clipers clean straight away it doesn't seem to damage the paint on them. If all goes well there shouldn't be too much fluid in the cloth. I expect there are good Health & Safety issues against doing it like that, though, so don't do as I do, natch.

PS I don't suppose it really matters which calipers you have, the principle will be the same.

i've never heard of that method. sounds like a good trick for difficult situations

BTW i've never seen original caliper paint on a bike damaged by brake fluid.