vented brake cylinders
vented brake cylinders
(OP)
Generically, at least on pre 1990 vehicles US cars master cylinders have a bellows under the cap to compensate for fluid level changes.
Seems like European cars have caps vented to the atmosphere.
Motorcycles use bellows, probably to prevent leakage when bikes tip over.
Does anyone know of applications that are exceptions to this "rule?"
Seems like European cars have caps vented to the atmosphere.
Motorcycles use bellows, probably to prevent leakage when bikes tip over.
Does anyone know of applications that are exceptions to this "rule?"





RE: vented brake cylinders
One way or another, you do need to allow _something_, be it air or bellows, to follow the reservoir's liquid surface down as the linings wear and the wheel cylinders extend to take up the slack.
Mike Halloran
Pembroke Pines, FL, USA
RE: vented brake cylinders
RE: vented brake cylinders
Do the vented to atmosphere cars also use silicone fluid? Less hydroscopic than petroleum based fluids.
RE: vented brake cylinders
RE: vented brake cylinders
Volvos with which I'm familiar (240/740/940/850) between 1975 and 1996 have Vented cap screw on and Dot 4. Yes they have plastic reservoirs. Girling and ATE brake parts.
1980 Yamaha 850 motorcycle - no vent, rectangular plastic translucent reservoir, 2 screws secure cap, Dot something fluid.
Here is a round screw cap with bellows, but it is for Motorcycle, thus has spill/tip risk.
https://store.bevelheaven.com/brake-related-parts/...
This 1940 Chevy MC appears to have a vented cap, but I'm guessing polymer technology of the pre-war era might have made a molded bellows too high tech for production.
I was also thinking the ventless design was "better" in regards moisture absorption.
I guess I would have expected DOT might have stuck their nose into "requirements" for US cars by the 60s, driving the bellows design, since a vented cap would seem to be the economical choice. But then the imports would have had to follow suit.
Even (some) of the M-cyls mounted under the floor, and thus subjected to splash and submersion seem to lack bellows, suggesting a vent is in action.
http://www.studebakerparts.com/studebakerparts/sto...
RE: vented brake cylinders
On motorcycles (at least some), even when upright the fluid level is above the gasket line due to the angle of the handle grip. The recharge port is on the uphill side (toward center of the bike). So it isn't purely a "tip-over" consideration.