Rear brake line size

[331efiblue66]

I ordered pre-bent stainless brake lines from CJPony, and the rear feed line is 3/16". My new master cylinder with prop valve for dual discs has a 1/4" line to feed the rear of the car. I know just enough about fluid dynamics/displacement to be dangerous. The prop valve is not adjustable for the rear, and I know the master cylinder piston is gonna displace a certain amount of fluid every time I step on the whoa pedal. Is the smaller feed line to the rear going give me too much rear brake bias? Do I need to upsize the rear feedline to 1/4", or is the 3/16" line gonna be ok? Thanks

 

[2+2GT]

OK, I've never seen a 1/4" brake line. Send it back. Fluid dynamics should tell you that the larger tube will simply slow the movement of the fluid within the tube, the movement at the MC and brake is unchanged. The larger tube will make it almost impossible to get air bubbles out, though. I would regard this as a "bad thing" in a brake.


Unless you have some really compelling reason, don't use SS, either, it's a real PITA. Hard to bend and rebend for the inevitable mis-match in shape, and tucking it around other components during installation will make you weep. And unless your alignment with junctions is perfect, the inverted flares will leak.

 

[331efiblue66]

Ok, to clear, the line IS 3/16", not 1/4". I was wanting to know if it NEEDED to be 1/4". The lines are PRE-BENT, ready to install in the car, and as far as misalignment and leaking, I've been a plumber/pipefitter for 23 yrs now, not to worried about getting it to line up and not leak. Thanks for your reply!!

 

[rbohm]

unlike the fuel system, the brake systems operates on pressure not flow, thus it doesnt matter what size the line is as long as the fluid can flow well enough to transfer the pressure. the smaller line is used to make it easier to bleed the system of air, but you would get the same system pressure whether the line is 3/16" or 36", as long as there is no air in the system.

 

[67rcks]

A lot of antique cars have 6mm or 1/4" brake lines. Most clutch hydraulic lines are made 6mm or greater to achieve faster response.

The 1/4" MC port goes to the distribution block, not to the rear. There must be OE 1/4" tubing available.