Brake line size changes

[Crafty]

Looking at the braking system on my '55 olds..

the original set up had a large,  single flexi from the master cylinder to a distribution block on the chassis, this split front and back, which was all plumbed in (I think but will check) 1/4" line.

I'm using a modern master cylinder, front is using GM calipers (typical hod rod kit). I'm using the original rear end.

The master cylinder has two outlets, thinking I may try and arrange a horizontally split system, so if I get a problem both axles will be braked by the "good" circuit.

Question is if I want to drop to regular brake pipe size (3/16th?) will it be okay on the rear?
Half of me says the pressure will be the same, so no problems, the other half says there is less fluid movement, so braking effect would be reduced.

Obviously I will have to run hard line to each wheel and then go to the caliper / cylinder with a flexi.

Thanks for the help.

[enjenjo]

Total fluid displacement on a properly adjusted brake system is under 10 CC for all 4 wheels, so 3/16 or 1/4" line are both suitable. 3/16" line has a slightly higher burst pressure, which is also unimportant. Ignoring antilock brakes, GM and Ford use front/rear brake splits, with a couple exceptions. Chrysler uses both front/rear, and LF,RR/RF,LR splits, as do some foreign cars.

Now, in my opinion, having brake failure at one end with both systems, I prefer the front/rear split. The reason is, on wet or icy roads, the diagonal split tends to turn the car under heavy braking, and a front/rear split doesn't. At higher speeds it will do this even on dry roads, which can have dire consequences.

If you do decide to use a diagonal split, you will need a 4 port master cylinder that is designed for that use, to make it work properly.

[Crafty]

Thanks for the help.

I was thinking about the diagonal split and realised it would be a pain for the plumbing, forgot to mention I was planning on using an adjustable proportioning valve, so I could ensure that the majority of the braking is done by the front (don't want the rears to lock first). So it'd be much easier if I did a front/rear split. I hadn't thought of the problem of the car turning in a failure.

A friend is using the same servo, master cylinder and calipers on the front with an 8" ford rear. His brakes are very good and have a decent pedal, so given the only difference is the rear end hopefully mine will be good too.