Bleeding brakes

[Mojoman]

I have bled the brakes on my cheap Tektro brakes in the same way as I bleed brakes on the car, i.e keep resevoir topped up and squeeze the lever, open nipple, let the fluid squirt through, and still holding the lever against the bar, tighten the nipple. Repeat until you are certain you have flushed new fluid through.

[SwissVan]

Maybe it has something to do with the age of the fluid? I assume air could be pulled into the system when the new oil interacts with the old.

 

I'm a novice when it comes to mtb hydraulic brakes but I have encountered this type of problem hundreds of times on the pisscats i used to work on and often wondered HTFlip air got into the system. Evolution tought me that whenever a system is opened to the atmosphere murphy will push / pull / insert some air in before you close it up eventualy requiring a proper bleed usualy from the lowest point possible upwards.

 

Furthermore on mtb systems the small amount of fluid in a system probably magnifies the effect of even a miniscule (sp) amount of air that could already be trapped (invisibly)in the new fluid or "sucked in" during the open / closing phase of operation.

 

Bladdy nearly as bad as trying to align / eliminate V brake pad rub....

[Cassie]

Ok, here is a suggestion - I haven't tried it myself, but is almost certain it will elliminate any air intrusion into the brake system.

 

On closing the reservoir (which should almost, if not, spill some brake fluid due to being overfilled) do not tighten the bolts entirely....THEN, from the bottom nipple push some more fluid up into the sytem till it starts overflowing from the reservoir...then tighten these bolts well (to spec).

 

I'ms sure this will expell all possible air at the top of reservoir - just beware not to introduce any air into the system from the bottom!

 

and Bob's your uncle....

 

@mampara - what about getting air in through the pistons somewhere in the process? Unlikely, but still a possibility...