hey all,
i have done a sas on my 90 F150, i have dana 60 front and 10.25 rear out of 95 F350. im running my brake lines now, my question is regarding the size of them, i have my factory f150 master cylinder, which im sure wont move as much fluid as my new brakes would like...but do you think its really going to benefit much (if i keep my factory master cylinder) and switch to 1/4 lines? id still have an adaptor at the master cylinder anyway. im asking because i just realized the wheel cylinders require a 1/4 fitting and i just tried to run 3/16 lines, and i believe the front will be the same way. should i just put my 3/16 to 1/4 adaptor at the rear cylinders and at the front hoses and call it a day? or should i switch to 1/4 lines?

i figured larger lines wont make much more difference if i still have my factory master anyway. any thoughts is much appreciated!!

thanks!!
Andrew

 

the 3/4 ton uses 3/16 line with the larger nut

 

ohhh ok. good to know. so me keeping my 3/16 lines prob will be ok then. ? i will just use adaptors at the rear cylinders and the front hoses if i need them. thanks!

 

I'm sure that others will have different opinions, and someone might even have facts backing them up (not all opinions do). I'm a mechanical engineer, which means I pretty much know what I'm talking about here, but I don't pretend to know everything. But my opinion (and yes, it's just an opinion) is that the size of the line can't matter all that much.

The lines are full of fluid and they stay full of fluid. You don't change the amount that's in them as you work the brakes, you just push some in one end and push the same amount out the other end.

The sizes of the master cylinder and the wheel cylinders (or caliper pistons) is critical. Those will change pedal effort and could run you into trouble where you can't push enough fluid into the wheel cylinder / caliper to get full braking.

If there was a lot of flow you would lose pressure due to the restriction from smaller lines. But very little fluid flows in a brake system, so 3/16" lines seem fine. And I suppose smaller lines could get plugged more easily, but that doesn't seem to be a big issue.

Larger lines have a theoretical downside in that they have more area so there is more force on them from the fluid pressure. That would make them expand more when you hit the brakes which would give your brakes a spongy feel. That could be addressed by making the tubing wall stronger (thicker). And 1/4" isn't that much bigger so the difference might not be noticeable anyway.

Larger lines will hold more fluid. Not sure if that matters. I suppose it could be an advantage if the fluid gets contaminated in that a little contamination might disperse through more fluid and the result be a lower concentration of the contaminant. But I think usually contaminants stay pretty localized rather than spreading evenly through the fluid, so it probably doesn't make any difference anyway.

Just my thoughts.

 

those were some of my very thoughts, actually. i figured my weak point is going to be my master cylinder. BUT, my truck is not a 1 ton truck, does not weight as much as a 1 ton truck, or will haul as much as a 1 ton truck. so im hoping that it works out alright with just my factory master cylinder, even though i have the 1 ton brakes. i too, did not think line size would make a whole lot of a difference.

 

I doubt ur master cylinder will be a problem f-150 bore 1-1/16 f250/350 1-1/8 bores

 

Bob, that was about the best explanation of brake system function i have ever read.
good job!!!

i upgraded one of my trucks years ago to the 1 5/16 bore master cylinders to try to relieve a spongy pedal brake problem.

the driver hated it after the conversion. he said all he had to do was look at the brake pedal and he would face plant the windshield.

i thought the brakes worked perfect after i did it.
i was going to do it to all my trucks as the masters went out, but i ended up closing shop and selling all hte trucks to their drivers due to the pay rate for escorts going down the toilet. in 8 months the rate went from $80 per hour to $25 per hour.

 

I don't know the sizes, but if that's what they are, that means an F150 master cylinder has 89% as much piston area as an F250/350 cylinder. That means you'll have to push the master cylinder 11% farther to get the same braking as you'd get with the "correct" master cylinder (the smaller piston needs to go farther to push the same amount of fluid into the wheel cylinders/calipers). That will only be a problem if you run out of travel, but it's not a huge amount so it could work out fine.

The other effect it will have is that you will only need to push 89% as hard on the pedal to get the same braking (89% as much force divided by 89% as much area gives the same fluid pressure). This probably wouldn't be very noticeable.