Do brake lines need to run downhill?

They should be fine as long as your master cylinders are highest point in the system

The film strength, (viscosity) of the fluid keeps it as a collum within the small diam. of the brake line.

Annual quick bleed prevents moisture contamination in the system, also needed in your auto's.

Tom

It is easiest to bleed the brakes if the slope of the tubing is continuous, but it is also possible to avoid air bubbles with some high spots. Especially if you have translucent tubing, you can see the fluid as it rises in the tubing and follow potential bubbles (assuming you fill from the bottom). If you fill it slowly, the bubbles may get trapped in a high spot, but because of the viscosity of the fluid, if you fill it fast enough, the bubbles may not manage to collect anywhere.

Do brake lines need to go down? I guess not, Jason. Look at a helicopter rotor brake instalation. The master cylinder is down in the cockpit and the rest of the instalation is several feet higher up on the rotor mast. A hydraulic brake is a hydraulic brake and they seem to be trouble free.

Bob

Thanks all for your replies!

Jason,

These are all good replies. I have run into the problems you mention. For my application, I just open the bleeder screw on the brake caliper and force fluid from the bottom up through the system and let it flow out of the master cylinder reservoir. Perhaps messy, but there is more than one way to bleed a system and this works.

Jason,  Everything I read about brake lines said they should slope downward, however, when I built my Kingfisher Amphibian, the brake lines had to rise from the master cylinders and then go down.  I had no braking problems with the up and down lines and I agree with Donald Prosser's method above, about the way to bleed them.  I used metal lines with short flexible lines at the master cylinders and down by the brake cylinders at the wheel.

Jason,

Iif you are really concerned about trapped air in your brake lines,

simply add a bleeder valve inline, (not recommended)  at the highest point.. 

No more problems,  but triple  the unneeded work,  if they are maintained normally, 

as prescribed.

Brake lines are a "closed" system. the only way for air to enter, is for it to be admitted manually.

(not prescribed.) i.e. low fluid levels in master cyl, etc.

OR...

If there is a loose fitting, or a crack, pinhole, or corrosion in the line,

air , is the  very least  of your problems as any of these can lead to brake failure.

Regular maintenance is the key to avoiding all problems.

If you bleed it properly when installed, and  check it regularly it will tell you,

 if there is a problem developing, long before it becomes dangerous.