Brake bleeding-where am I going wrong?

[flymo]

I've found the quickest way to get started on a dry system is to connect up a hose to the bleed nipple on one caliper, open the nipple and keep pumping away on the brake lever, slowly to allow the fluid to enter. Keep the nipple open through out this process.

Dont bother with the bleed kit until you get fluid coming out of the caliper into the tube. Do the same on the other caliper until you see fluid escape into the tube.

Then nip up the bleed nipples and use your bleed kit.

[Biker Biggles]

Originally Posted by PJinUK

Just re read your bleeding process.....
might be irrelevant but I usually undo the bleed nipple, then squeeze brake lever until fluid come out.
then , with fluid "oozing" and the brake lever at 3/4 closed toward the bar, close the bleed nipple.
then its release brake lever,
open bleed nipple
squeeze brake to 3/4
close nipple
release brake.Once I only get fluid out of bleed nipple,,I do like ging6996 and jiggle the hose up to the top banjo bolts and blleed them,,i.e
undo banjo
squeeze brake
tighten banjo
release brake until only fluid appears,,
then finally check small hose to master reservoir for air by jiggling that...
god,,never typed so much ,,,stiff fingers now

Read this post carefully and compare to what you are doing.The above sounds like what I do,in that I open the nipple then squeeze the brake lever to expel fluid(and air),then close the nipple before releasing brake lever.I dont rely on non return valves from Halfords to prevent air sucking back into the system.

[rowdy]

Biker Biggles, this is exactly what I have been doing. If you read my original post it says to start with I connected the brake bleed kit, undone the valve and pumped the lever. I done this for about 5 minutes then resorted to the way that has been said to do it and that I said in my first post, i.e. not relying on the one way valve and undoing the nipple then releasing the brake lever only once I'd done the nipple back up and not pumping the lever until the nipple has been done up.

Have been trying to bleed the master cylinder without pumping the lever whilst the banjo is slightly undone this time for about half an hour but still no signs of fluid seeping from the banjo's and now it's bl**dy snowing.

Rowdy, it looks like you discovered for yourself that those bleed kits are a mugs game. The other method is effective if not a little tedious. Better yet is a bleed pump which makes the job a snap. Easy means that the job is more likely to be done on a regular basis avoiding a lot of brake related woes.

Cheers

[embee]

Just a silly question (I hope), but you have taken the diaphragm out after removing the master cylinder cap?

[rowdy]

Originally Posted by embee

Just a silly question (I hope), but you have taken the diaphragm out after removing the master cylinder cap?

I haven't removed the master cylinder cap, am trying to bleed it from the banjo bolt as described by 21quest.

[lazymanc]

Originally Posted by rowdy

I haven't removed the master cylinder cap, am trying to bleed it from the banjo bolt as described by 21quest.

I've never done this so I could be talking a*se but if you haven't removed the resevoir cap then I would assume all the fluid will be being held in the system by vacuum at the resevoir, kind of like when you put your finger over the top of a straw.

Originally Posted by rowdy

I haven't removed the master cylinder cap, am trying to bleed it from the banjo bolt as described by 21quest.

Its not a mastercylinder, it is the reservoir that holds the fluid. The master cylinder is what the brake level is attached to and pushes the fluid through the system.

It sounds to me that you do not have enough fluid in the system, you will have to remove the reservoir cap to put more in.

Nice and simple/basic way, remove the reservoir top and top it up with fluid. Place an 8mm spanner and a piece of hose on the bleed nipple. Pull the brake lever in and undo the nipple, tighten the nipple back up and then release the lever. Do not release the lever before tightening up the nipple, you will draw air back into the system! Repeat this process, whilst insuring the fluid is above the minimum line in the reservoir, until the fluid starts to run bubble free out of the nipple. Repeat the process on the other side, the lever will start to feel harder to pull (bear in mind the lever will only start to become harder to pull when both lines are bled).

Once both lines are bled zip-tie the lever back and leave over night, this will force the air to the bottom and in the morning one last twiddle with the nipples will release any trapped air.



If you are still having problems you then go to bleeding the banjo bolts, but first double check everything is done up correctly other wise you will be wasting your time on every attempt.

Bleed Nipples: 8Nm
Banjo Bolts: 23Nm

[Red Herring]

Often the problem is getting rid of air that is trapped in the middle of the system. Air rises, so trying to push it out of the bottom of the system is hard work, on some bikes it goes up as fast as you are trying to push it down. This is especially true on a system where there is a link pipe between the two calipers that goes up and over the mudguard.

The first thing to do is look at your system and identify potential air traps as described. Ideally the bleeding point needs to be the highest point, but this isn't always possible. If you do have a loop over take off one of the calipers and hang it from a handlebar so any air in the crossover can go up towards the caliper. Next look at your master cylinder location. If you have a bike with clip ons then with the bike on a paddock stand the right bar is often pointing down slightly, and with a lot of master cylinders this means the banjo end will be higher than the body of the cylinder, another potential air trap. Either put the bike on the side stand and turn the bars to the left (usually enough) or undo the master cylinder and hold it slightly banjo end down.

Then take the top off the reservoir and put a piece of clear piping on the lowest bleed nipple and open it. Try to jiggle the system (pump the lever etc) so that you get about 10 inches of fluid into the pipe, then open the bleed nipple on the other caliper (which should be higher than the first) and blow down the pipe with the fluid in it, forcing the fluid back into the system until it comes out of the other caliper bleed nipple (but under no circumstances empty the pipe completely, if you do you will be blowing air in). Sometimes this takes a bit of puff, I've cheated and adapted a bicycle pump) but what you are trying to do is push the air up the system, rather than down. Once you have tightened the other caliper nipple keep blowing until no more bubbles are appearing in the reservoir. You may need to top up the pipe by either pumping the lever a little, or doing what I do which is take the pipe off, put it in a bottle of fluid and suck some up into it.

One other tip, if you have taken a caliper off stick an old pad between the pads, otherwise when you pump the lever you may push the pistons out which at the very least will make it harder to replace the caliper, at the worst they can actually come out far enough to jump a seal. Oh, and keep an eye on the reservoir level, remember the more fluid you introduce at the bottom the higher it goes, take some out if it looks like overflowing.

Good luck.

[rowdy]

Problem over, thanks for all your replies.
Decided to take calipers off empty master cylinder, fluid reservoir and start again, bleeding the m/c first. This took a couple of minutes, then on to each of the calipers, which in turn took only a couple of minutes each side, all in all about ten minutes to do the lot. Tied the lever back to the bar (well as far as it'll go) but due to the inclement weather decided to wimp out and take the car to work today. Will give them one last bleed when I get home later and test ride the bike once my road is a little less like an ice rink. Once again thanks for all the helpfull advice.