Brake bleeding tips

[bobsmith]

I've just gone and cleaned my brake parts out and put some new grease on them a few days ago and went to bleed them. Now the rear brake was easy enough, but when I went to do the front one, I kept on pumping the brakes but they just wouldn't pressurise (read: it felt spongy and it didn't go away when the brake pads moved all the way to the and they were in the right position) no matter how much pumping and bleeding I did.

I wasted several hours doing this, did some search on google and here and found out that problem is most like air bubbles stuck just below the master cylinder.

Now all the posts suggested that I would need a pressure bleeder to force the brake fluid from the bottom to get the air out and should take it to the shop but of course being stubborn I couldn't do that. (besides the fact that I've got no money...)

So here's what I did and fixed my problem within 15 minutes (wish I thought of this earlier) If you're having trouble of no air bubbles coming out from the calipers (ie only brake fluid coming out suggesting that the calipers are bleed of air) but the brakes still feel spongy here is what you can do:

1. First bleed the brake as much as you can.
2. When you've bleed the brake so that the slave cylinders (the brake caliper) is full of brake fluid (you can tell by when you're bleeding that only brake fluid is coming out) get a G-clamp and start pushing the pistons back.
3. Hopefully that should force the brake fluid up the line to the master cylinder and should get that airbubble out. Becareful that you don't spray yourself with brake fluid as you do this (picture you croutching down pushing the pistons back then the air bubbles come out the top and you had too much brake fluid in the master cylinder and it goes all over the place... not fun)
4. Now pump the brake and let the pistons out a bit then press them back again and repeat this a few times until the pistons come out [insert a word that I can't think of here... (well?) ] with the pumping of the brake lever (before you start pushing the pistons back to bleed the line and the master cylinder you'll see that pumping of the lever doesn't push the pistons out as well as it should, well now it should push them out quite easily)
5. you're done, reassemble the brake caliper then bleed the brake as per normal.


Now I've written this with my limited knowledge of how the brake systems work and from my experience with the brake bleeding nightmare. Take into account that I've only bleed 4 brakes before if anyone can suggest a correction to these please let us know!

I wrote this because I wasted 6 hours and almost a whole bottle of brake fluid trying the bleed the front brakes, hopefully this should save some time for another person with similar problems.

[surfer]

Just a thought did you consider one of those cheap kits from somewhere like repco for bleeding brakes? Or of making your own from a jam jar and a bit of see through plastic hose? Saves hours of pumping and saves brake fluid from being squited all over the place.

[scracha]

Just put elastic bands on the brake lever, leave overnight and then a quick bleed in the morning.

[bobsmith]

Just a thought did you consider one of those cheap kits from somewhere like repco for bleeding brakes? Or of making your own from a jam jar and a bit of see through plastic hose? Saves hours of pumping and saves brake fluid from being squited all over the place.

Yeah, I do have one but doesn't help at all when there's a airpoket trapped under the master cylinder...

[vagrant]

I turn the bars on th e Blade hard left, which levels out the master cylinder, and then gently pump the lever while tapping the banjo bolt with a screwdriver handle. This lets the bubbles come back up out into the reservior.
The RC30 is a bit harder and easier, I pull the master cylinder and calipers off, mount the master cylinder in a vice and use wooden spacers in the calipers.
It works well and makes the bleed a lot easier, and I have lots of room to feed the calipers up and down the the forks.

[bluninja]

I bleed and then leave the brake lever pulled on hard overnight, then check and bleed as required in the morning.

[erik]

what does leaving the lever pulled hard on overnight actually do?

[bobsmith]

what does leaving the lever pulled hard on overnight actually do?

I would like to know too...

Vagrant.

When you're talking about taking the master cylinder off and putting wooden spacer on the caliper, is that so that you can put the caliper above the master cylinder???

I know next to nothing about bleeding brakes (besides the very basic I've talked about) and I'm really confused now......

[imdying]

what does leaving the lever pulled hard on overnight actually do?

Blocks the compensating port in the master cylinder so nothing can get through... i.e. nothing.

[bistard]

Have you tried cracking the banjo bolt at the mastercylinder??If not put a rag under the whole assembly,pump the lever,then crack the banjo with the lever held in,tighten up banjo & release the lever
Just a small amount of pressure on the lever,otherwise it will squirt out with pressure

[The Stranger:Me]

Had a similar problem last time I did my brakes.
So this time I got a banjo bolt with a bleed nipple in it for at the master cylinder. These are available from many bike shops. Shit what a difference and amazing how much air came out of the top, even though none was coming out the bottom. Worked better than the vacuum bleeder i.e. quicker, less hassle and used less fluid.

[R6_kid:Me]

I would like to know too...

Vagrant.

When you're talking about taking the master cylinder off and putting wooden spacer on the caliper, is that so that you can put the caliper above the master cylinder???

I know next to nothing about bleeding brakes (besides the very basic I've talked about) and I'm really confused now......

im guessing the wooden spacer is to take the place of the brake disc so that he can apply pressure through the system with it off the bike and not have to worry about forcing the pistons back to get them to fit back on over the disc.