This is sort of a companion post/supplement to my Mongoose Big Brake post (go there for links to resources on cable cutting and bleeding). Worth putting up separately as its a topic that comes up from time to time in my travels, and putting it here will let me just link it into a discussion.
These directions assume you are working with Magura brakes. However, they should translate reasonably well for a generic application (for best results find specific instructions for your model).
Next time I do it, I’ll take some pics so I can spruce up the page a bit.
- Toss a small towel on the ground under the caliper you are bleeding. Just in case Something Bad happens.
- Leave the caliper on the bike.
- Get everything ready because once this process starts oil is going to be dripping out of and onto things. ‘get ready’ means in part to get your lower syringe with the bleeder hose fully filled in advance, with the hose filled with fluid not air bubbles.
- Loosen the lever on the handlebars and re-orient it so the brake reservoir is level to the ground
- With the top bleeder still in place, which will limit the rate of fluid loss somewhat, open the bottom bleeder and haul ass to get the syringe screwed onto it. I usually manage to get only a small dribble onto the caliper. Tighten the syringe onto the bleeder with an 8mm wrench and make sure it is on tight (not ‘crank arm’ tight… go just a skootch past ‘snug’).
- Remove/open the top bleeder. Since the bottom bleeder on the caliper is closed, nothing is going to be leaking out yet. Attach the top syringe/reservoir.
- Do one cycle of bleeding, bottom to top and back to bottom, gently, to establish vacuum and ensure you have a good setup and don’t have any leaks or surprises. While doing this, periodically tap the caliper and fluid reservoir in the lever with something firm like a *small* dead blow hammer (or the handles of your pliers) to help dislodge any stuck bubbles.
- With a full bottom syringe, push the fluid up through the system… hard this time. Not enough to break the syringe or do something crazy, but enough so you can see the oil well up in a wave in the top syringe. On the return stroke back down, be gentle so you don’t suck any air in via the edges of the top syringe seal.
- Repeat Step 8 until you no longer see tiny occasional streams of bubbles. You can stop when fluid is in the bottom syringe, drained from the top syringe, with just a bit of fluid in the top syringe (say… 2-3mm or so) for the next step.
- Using the 8mm wrench, break the lower syringe loose and as soon as you are able, spin the thing off the bleeder by hand. Have the bleeder screw ready to pop back on asap because fluid will start dripping out immediately. Important: The little bit of fluid you left in the top syringe will keep the reservoir topped up unless you screw up and are too slow to get the bleeder bolt back on..
- Remove the top syringe and replace the cap screw, taking care not to overtighten … its a plastic bolt and need to ONLY be snug (0.5nM, officially).
- Mop up. Chances are good you only got a little on the caliper from Step 9.