On my 70 Skylark the brake lines that go to the rear are 1/4" and the fronts are 3/16". Being cheap and not wanting to buy 2 rolls of brake line is there any reason that all lines cannot be 1/4". Rears are drums, fronts are disk.
Larger diameter line will decrease brake line pressure, but the other issue will be proportioning. Since you are reducing pressure, you are reducing braking efficiency to those brakes, and with the proportioning, if you have to increase pedal application to get the same braking on the affected side, you will be "over braking" the side that was originally 1/4 inch. I do not know off the top of my head how much the ratio will change, but it will change.
I am thinking more of volume instead of pressure, it takes more fluid to pressurize a 1/4"" line than a 3/16" line. It is engineered to match the capabilities of the master cylinder to pressurize both circuits with same pedal travel. It may have more to do with timing and proportioning, the max pressures attained will not change with line size. Think of airing up a small tire vs truck tire with same 60psi source, it simply takes more volume with larger tire. Brake line size will simply affect pedal travel. Timing of application may change slightly from front to rear compared to oem original sizes. With the master cyl having 2 pistons traveling together, volume may indeed affect individual circuit pressures somewhat as stated by TrunkMonkey.
Yep. Thanks. :bglasses: When hydraulics are distributed, the branching and division require less diameter to keep pressure, flow and volume proper in the entire system. My greatest experience is from aircraft hydraulic systems (and mechanics) but I have been out of both for over 25 years, so I am not proficient enough to try and get into minutia. Disc systems require different size tubing for operation in split disc/drum systems and often fron to rear are also differing in tubing diameter. There are a lot of factors involved in the design and implementation, and swapping things around may well work in a general sense, but braking, especially as speeds and mass are increased, is a safety issue and should be ventured into with the understanding of affecting the proper operation. My real point was to address that changes, while not seeming to be a big deal, can be critical safety issue and that was something I have had drilled into me my whole life. I want folks to have fun and be around a long time.
Just buy a roll of 1/4" for the rear and some pre-made lengths for the front, it won't cost much more. The biggest problem with using 1/4" on the front is that the junction block and hoses are made to accept 3/16" line. You may have to put 1/4" to 3/16" adapters on the ends. I don't see an issue with either a line pressure or volume (pedal travel) difference. The brake fluid, for the most part, doesn't compress under pressure, so volume/pedal travel won't change. The pedal force and master cylinder piston size will produce a certain amount of line pressure. I believe the resulting line pressure would be the same in a 1/4" line than it would be in a 3/16" line. Hopefully Devon will chime in.....
