Front brake Resevoir problem? Bleeding Brakes!!!!!

[Timbo45]

Hi Folks

I've not been on for a while mainly because I'm close to BryanJ and he HAS become my world of knowledge!

I'm sure Bryan will know the answers I'm looking for but our paths have crossed in the night recently and I've not managed to speak to him about my problem.

Anyway, master cylinder rebuild, new BOTTOM braided hose (Thanks to BJ), new piston and seal (again thanks to BJ for getting the old piston out), new bleed nipple (bet you can't guess who did that?) and it just wont bleed out!

It's bleeding to a certain extent as The brake gets about 25% on it right at the end but thats it. i have checked all the connections and all seams good. One thing I have noticed is that if I try to pull the lever in with the top off the resevoir fluid spurts out of the hole with the small pin hole in it. is this correct or does this indicate that the master cylinder is not functioning correctly?

Any help would be VERY MUCH APPRECIATED as I'm so close to finishing my project.

I will post pics when it's finished but not before:-)

Thanks in anticipation.

Timbo

[mickwinf]

im having exactly the same problem ! If you leave the resovoir top off while bleeding fluid spurts all over. Mine bleeds so no bubbles appear but still lever pulls back almost to handlebars. I also have rebuilt the master cyl and caliper and renewed the lower hose with a braided one. Please help us!!

[Bryanj]

Its normal for fluid to squirt out of the small hole, if fact thats one of the "tests" if the brake is binding!

Is the caliper adjusted to the correct 6 thou clearance?

Q Does the lever come all the way back to the bars or not if not
Leave it a couple of days and re-bleed

i have also found that two things can happen;

(1) after a complete strip and rebuild the lever will get firmer after a while so as long as the brake stops you without the lever hitting the bars live with it

(2) a lot of levers wear at the pivot and there is frequently a lot of "Play" before the lever starts moving the piston--New lever and pivot bolt will help this and i have seen, on US master cylinders, a nickle araldited onto the piston end to take up play.

[daz]

I found if you gently pull the lever in a small amount, as in pull in release constantly, a very small amount so fluid does not squirt every where, you get small air bubbles released that eventually bleeds the brake. Has worked for me a number of times cheers Daz

[Timbo45]

Thanks Chaps for the support, I think you may be onto something Bryan,
Just about to go and check my clearances!!!!!!!

I did notice if you pull the lever in slowly the squirting doesn't happen.

I was thinking maybe the master cylider was assembled incorrectly and just quirting the pressure back into the resevoir instead of down the hose.

i'll let you know how things go.

[Timbo45]

Clearance was ok so I'm back to the drawing board.

Left it now cos the swear box is full!

[kent400]

It's fair to say the front brake is is a pig to bleed. The method I've used seems to work well. place a tube on the bleed nipple with the other end in a jar with a small amount of fluid in it. Open the nipple and just let the fluid run though without pumping it. Keep an eye of the fluid in the master cylinder of course. You will probably be surprised by the amount of air bubbles you will see in the jar as the fluid flows though the system.

I put silicone brake fluid in my front brake after resealing the master cylinder and caliper. Some suggest this should not be used as it has an adverse effect on the seals, well it's been in there for about 8 years and all is well. Silicone fluid does not absorb moisture and will not damage paintwork. The bike has just had an MOT and the tester commented on how little travel there was of the lever despite the fact it still has the original brake hoses. I'm not sure if the silicone fluid has any effect on the amount of lever travel but at the time the real advantage to me was there could be no damage to my newly painted tank should a spot a fluid drop on it using silicone fluid.

[florence]

It is worth remembering that air bubbles can be too small to see easily with the naked eye and can remain in suspension in the fluid.  The idea with bleeding is to replace all the fluid in the system with new stuff which will not have any air in it.  Although it is tedious the only method I find to work well is to open the bleed nipple, pull back the lever, tighten the bleed nipple, release lever, repeat and keep repeating until it all feels firm.  Don't forget to keep checking the level in the master cylinder and replace the cap each time or fluid will squirt out, this is normal.  It takes a while but should work unless there is something wrong with your brakes.  Make sure you have adjusted the caliper as explained in the manual.  If you bleed lots and it still feels spongy you may have an air lock.  Try moving the wheel to a different angle to make sure the bleed nipple is at the highest point.  Do not reuse old fluid.

[jcknapp]

Is the  nipple a newer one where you don't have to open the nipple? There are some newer nipples where you can bleed the brakes on your own which i actually have. I completely had to dismantle my front brake caliper unit. I examined it and it was pretty pitted. So I fought getting out the piston and seal. A bunch of nasty old rusty brake fluid and junk came out and I completely cleaned out the caliper unit, replaced the piston and seal and went to a braided cable with a new banjo bolt connection with a copper washer. I also replaced the master cylinder. Now to get brake fluid going through the line is pretty easy and also when you just bleed the brakes in general. If you don't have the nipple where you have to open and close the brake nipple then this is how you do it. You open the nipple quarter turn, squeeze the brake, close the nipple and repeat. you keep doing this till the air gets outa the line and no more air bubbles occur. You will know when this happens. As florence explained this is the way to do it. Also use the correct DOT 3 fluid and run a clear tube into a jar so you can see the air coming out. The toughest thing for me was to maintain a tight seal on the braided cable connection to the caliper. A copper washer did it good though. Hope this helps even though it was more or less said by others.

[mickwinf]

Timbo did you get this problem sorted, i have tried all these methods with no success so bought a new master cyl from silvers, still no brake! the only thing i havent replaced is the top hose as the brake was working before i stripped it down. When bleeding i dont get much movement of the fluid in the pipe, it moves about an inch then flows backward to the same place. I have new master cyl, bottom hose, piston and seal.Caliper is adjusted correctly and free, i have tried suction with syringe and pushing caliper piston back manually all with no luck, the lever comes back to handlebars with no resistance although the brake does work enough to stop wheel rotating.Please help !!

[Bryanj]

OK this method i have never had fail BUT YOU MUST WEAR GLOVES and idealy have an assistant, also keep the reservoir topped up.

(1)Disconnect the top hose at the master

(2)Cover up everything that brake fluid can spill onto and put a gloved finger over the outlet of the master

(3)Pull lever and with it held in release and re-apply finger

(4)Repeat 2 & 3 until fluid is squirted out from under finger with some force

(5) whilst holding lever in get assistant to reconnect top hose

(6) now bleed using the bleed nipple

[Green1]

I two had problems with my brake leaver coming back to the bars I found if you bleed the brakes as florence explained and then pull the leaver in and tie it up overnight it pushes microscopic bubbles out.Release it in the morning and it should be firm it never fails. 

[mickwinf]

thanks will try these methods next weekend although i did try tying the lever on the old master cyl.

[mickwinf]

this problem seemed to sort itself out, i just left it for a few days without disturbing it and it has now got a much better feel.Is this because the air bubbles gradually float up to the top?

[Bryanj]

Yup