Rear Brake Bleeding [How To]

[ChrisBurke]

Hey all,

I just wrote a lengthy email to a customer on how to bleed his rear brakes (after purchasing rearsets and a brake light switch banjo bolt). I figured some of you may be interested in reading it...

* Firstly just a note about what/where the brakelight switch banjo bolt goes - it replaces the bolt into the top of the rearbrake master cylinder at the foot peg, and operate the brake light if there is no provision with the rearsets. As it is part of the brake/fluid system, you will need to drain the fluid before disassembly, and then bleed the brakes after assembly.

'To drain:
Get yourself a small size flexible hoses which slips onto the barb on the bleed nipple on the rear caliper. Remove the lid from the rear brake reservoir. Attach you lil hose to the nipple on the caliper, aim it into a container/bottle (away from you paintwork). with a tiny spanner crack open the bleed nipple about 1/2 a turn. Now (slowly) pump the rear brake lever until the fluid has stop squirting into the bottle (you'll get bubbles eventually) and the reservoir should be empty.

During this process keep an absorbent rag handy to wipe up any fluid if it gets onto anything.

Now you can remove/replace the banjo bolt in the master cylinder.

To re-bleed:
Once the bolt has been done up etc you ready to re-bleed the system. For rear brake I find it easier to remove either the cylinder assy from the peg, or the complete peg/rearset from the bike - as you are fitting rearsets you can just do this while their off. The aim is to have the master cylinder higher than the caliper (some ppl just lift the front of the bike into the air).

Close off the bleed nipple in the caliper (finger tight for now). Add some fluid into the reservoir. Keep in mind you are trying to move fluid in only one direction - from the reservoir to the caliper. Crack the bleed nipple open 1/2 turn, slowly push the brake pedal down (bubbles will come out of your drain tube at first). While the lever is at the bottom of the stroke, close the nipple. With the nipple closed, let the brake lever up (which draws fluid from the reservoir). Once the lever is at the top, repeat the process. Make sure the nipple is open while the lever is going down, and its closed while the lever is going up.

This process pushes the air/old fluid out of the system through the caliper, and draws new fluid into the system though the reservoir. Keep your eyes on the fluid level in the reservoir as it may take a couple of refills.

I like to repeat that process till I see good fresh fluid coming out of the drain hose with no bubbles (it doesn't hurt to do a few extras to make sure every last bit of old fluid/air bubbles are out). Now you can close off the bleed nipple properly and detach the drain tube. Pump the lever until there is good pressure.

You should be all done! Make sure everything is tight, and that you have good pressure before riding off! If you didn't get very good pressure after the re-bleed, you may need to repeat the process (sometimes its best to go for a ride and try it out/use them a little bit, and then come back and repeat). '

Im open to questions/comments :-)

Chris

[Foofie Foofie]

Thats pretty sound advice Chris, no probs. I have only 2 things id do differently ...

1) If they have a syringe, you pull out all of the resoivoir fluid manually. If they dont, crack the seal at the bottle by taking off the clamp and moving the rubber hoes just far enuf off that it dribbles out, making sure it doesnt come into contact with painted items.

2) Never drain the whole system and introduce air into the caliper (s) if need be, its a PITA and may need furether bleeding to get back 100%. I would loosen the rear line up and leave it full, this way when they do it up, they only have a tiny bit of air to flush that may get trapped in the line at the bolt thread, rather than working with the caliper dry. When finished hose down the area with a low pressure garden hose.

[Dingo]

moving the rubber hoes just far enuf off that it dribbles out[/b]

Mebbe you need to see if you can borrow Roosters new toy to fix that problem saf?

Nice guide Chris, Thanks for sharing.

[twowheels]

do you guys do the same when you are do the front brakes to?

[Stew]

I was always told as a apprentice to (on old cylinders) never push the master cylinder piston in more than the normal travel stroke. That is, if in normal operation the piston travels half the length of the cylinder then that is as far as you should push it. The reason for this is that during the normal life of the cylinder rust and pit marks will form on the unused section of the cylinder, when you push the piston over these marks it can cause abnormal wear of the rubber piston seals, causing more problems.
If you are fitting a new cylinder out the box, then no problems on how far the piston travels.