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hydro brakes: reservoir orientation on bent bikes? Vert=bad?
I ride mountain bikes a lot and am very familiar with hydraulic disc
brakes. Most current systems are "open", or have a fluid expansion reservoir at the master piston/cylinder (brake lever). If a bubble appears in the system, it can travel "uphill" through the system and escape into the reservoir. Bubbles in the system (other than in the reservoir) cause mushy lever feel since the gas pocket is compressible. The open system takes care of this problem if the bubble is able to escape to the reservoir. Many bents, however, use drop-grip-style bars which place the master cylinder in a vertical or sloped orientation. The hydraulic line arcs up to the handlebar and then descents into the brake lever (i.e. lever blade points down), effectively disallowing bubbles from migrating all the way to the reservoir. This can be seen on some Challenge Bikes models. Trikes which use hydro discs (Greenspeed) invert the master cyclinder (lever blade points up) so the reservoir is still at the highest point. Magura's rim brakes (HS 33, etc) employ a closed system (no reservoir) and work under the assumption that no bubbles will ever form and the brake fluid never will get hot enough to need to expand significantly, and even if it does, the volume of the system can be adjusted via a screw-piston. My question is, does anyone here run an open hydraulic system on their bent with the reservoir not at the system's highest point, and if so, what are the results? Frequent need to bleed? Mushy brakes? Do you remove the levers periodically and store them to allow bubbles to migrate up? Many disc-brake equipped bents employ mechanical discs. Is it for this reason or just because they are less finicky for the average user (I have both on my mountain bikes)? Thanks gentle bent folk. tscheezy |
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tscheezy wrote:
My question is, does anyone here run an open hydraulic system on their bent with the reservoir not at the system's highest point, and if so, what are the results? Frequent need to bleed? Mushy brakes? I have a Hope M4 on the front of my Speedmachine and a Hope Mini on the rear, with the brake lines running upwards before being routed along the tiller. No problems with feel or bleeding once they were correctly set up. The rear one is a bit mushy, probably because I was too idle to get it completely bled when setting it up. Do you remove the levers periodically and store them to allow bubbles to migrate up? No. Many disc-brake equipped bents employ mechanical discs. Is it for this reason or just because they are less finicky for the average user (I have both on my mountain bikes)? Probably because they're about half the price of hydraulics... -- Dave Larrington - http://www.legslarry.beerdrinkers.co.uk/ ================================================== ========= Editor - British Human Power Club Newsletter http://www.bhpc.org.uk/ ================================================== ========= |
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