hokiefyd 

Most recommendations is to bleed a hydraulic brake system from the caliper. This seems to be the "correct" method for both Shimano and Tektro, using a syringe at the caliper to push the mineral oil up through the system and out the reservoir at the top. But at least one resource (Worldwide Cyclery I think) shows bleeding from the lever side on a Shimano brake system, by filling the funnel with fluid, using a catch bag at the caliper side, and working with the bleed screw and lever to push fluid down through the system (making sure to close the bleed screw before releasing the lever so as to not introduce a vacuum). This is how automotive brakes are typically bled.

Is there any functional difference between the two methods? I reckon, if done correctly, they would produce the same result, right?

Tandem Tom

It seems like using the high point so that bubbles would rise to it makes more sense. But that's the only wat we do it in the shop.

wschruba

There's a good reason to go top down on non-rebuildable systems: to flush the dirt/other crap that works its way in out the less vulnerable side.

fietsbob

Its how it works in cars too, fill the master bleed the slave [Cylinders].

another trickle.. down.. practice..

plastic syringe pushing in on top, catch bottle at the bottom.

NB: Promptly wipe off DOT fluids, they eat at paint..




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hokiefyd 

Good point -- these are definitely of the non-rebuildable variety. They're Shimano's Altus-level hydraulic brakes.

Right -- however, in this case, they just used the Shimano funnel and kept it filled with mineral oil, and used the brake lever to flush the line. Crack the bleed screw, squeeze the lever (pushing mineral oil out the slave cylinder), tighten the bleed screw (to prevent sucking air), and release the lever. Check for fluid in the funnel (so no air is sucked) and repeat three or four times, or until 20-30 ml of mineral oil has been flushed through. A threaded syringe method seems like it'd work just as well or better. Either is intuitive to me (go from the top down with clean fluid).

Check. Shimano uses mineral oil, at least in this application, so I'm good to go there.

Thanks, all!

DrIsotope

Double syringes is the way to go. I'll nearly foolproof. At the end of the fill/flush, I just cycle a tiny bit of fluid back and forth until air stops coming out of the syringe at the lever. I don't trust the funnel method.

But yeah, flush with the help of gravity-- in through the lever, out of the caliper.

gsa103

Bottom up is likely better at getting air out. The shop procedure is essentially for truly empty lines.

Most of the time air is trapped at or near the caliper, and so a top down is equally effective and much easier.