Bleeding Front Brake

so i need to fix my brake line and will end up having to bleed the line, how do i go about doing it any tips? thanks


Are you mostly concerned on how to shortcut the line bleeding?

'Sorry if I'm telling you what you already know.

Get: -proper dot 4 fluid (I assume that's what your bike calls for)

-open or box wrench to fit bleeder screw

-phillips to fit master cover

-clean/new vinyl gloves

-clean peanut butter jar-approx.

-clean rags, paper towels

-clear plastic tubing, 1-2 feet, to fit bleeder screw

Maybe you could slowly and repeatedly pump the brake handle while holding the caliper end of the line up above the master until fluid comes out, being careful not to run master dry, refilling as necessary. Hold vinyl gloved finger over caliper end of line, when releasing brake handle during pumping operation, and while moving line down to attach and tighten it to caliper with minimal, but some unavoidable leakage.

Here's what I do for my normal flushing; I guess it would take a long time to flush the whole line this way---

Wipe off master. Secure bike. Push hard on master cover screws while breaking them loose a little bit. Loosen master clamping to handle bar; rotate master (and move handlebars to a steady position) to make reservoir level. Remove master cover; careful not to spill fluid on painted objects. I use a clean suction bulb (dedicated to brake fluid and kept in a sealed bag) filled with some fresh dot 4 br fluid to sort of gently flush the reservoir, stirring up sediment, etc., suctioning it up and depositing in jar. Don't suction too close to holes in reservior and don't try to suction all fluid out of reservoir- don't want to introduce air into system there. Fill reservoir with fresh fluid. Break loose bleeder screw just a bit. Gently snug it back closed. Attach clear tubing to bleeder screw, and put other end of tube in jar below brake caliper. Then slowly and steadily apply brake, and loosen screw; as you approach end of handle stroke, gently tighten bleeder screw, so that you don't suck air into caliper. Slowly release brake handle. Repeat actions stated in prior sentence, making sure to fill reservoir with fresh fluid well before it gets down to bottom, or you'll suck air in there! When no more air is seen thru tubing emerging from caliper and when handle doesn't feel spongy any more, you should be ready to sew it up.

Dispose of used fluids in marked container (like it came in) periodically at hazardous waste event.

I hope this helps. I'm not sure about bleeding the master itself---don't know if it has a check valve for bleeding it separately.

An even better method is to back bleed with a syringe attached to the bleeder screw via a rubber tube and forcing brake fluid back up into the empty reservoir.

It is much more difficult to get rid of air in the system the other way due to the fact that air bubbles rise to the top.

Would all of the air be purged out of the master cylinder if you pump fluid in from the bottom to push air out of the line?

Yes, the air bubbles would end up in the master cylinder reservoir and therefore purged from the hydraulic system into the atmosphere.

What type/brand of syringe/where do you recommend getting it? Do you keep air from getting introduced by just shutting off bleeder screw before disconnect?

I had a nongeneric 10ml syringe lying around that I used. I wouldn't try using one any smaller than that. Syringes are available from a variety of sources, however I don't have reference sources available at my fingertips.

Backbleeding is very easy to do, and it worked well the first time that I tried it. Just make sure to suck out all the old brake fluid from the master cylinder reservoir beforehand, and to tighten the bleeder valve before disconnecting the connecting tube and syringe.

The syringe method is the best. I will never use any other way again. I even had one of those high priced vacum things that would suck the fuild from the master cylinder. It worked like ass. I bought a $2 dollar syringe and I can change the fluild in 10 minutes.

Anouther tip is to flick the brake lever. That gets the last of the air out of the MC.

Great write up Chas_M

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