Rear brake line size

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.

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.

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.