ok brake guru's got a question or 2 for ya.

ive put 3/4 ton disk's on the 14 bolt going into my TJ, and ill be running the ford dual piston 1 tons up front. now here is me question...... the brake lines are fawkin huge on the ruber line for the rear caliper, since i need to run all new lines up to the frame anyway whats the best thing to do. reduce the line at the rubber hose? or reduce it at the frame, or just say fawk it and cut the hard line back near the master cylnder and reduce up there and run big fat lines as much as i can.

will the brakes be effected by the larger volume of the lines? will running large lines up to the frame cause a preasure point with the reducer?

to be honest i dont know enough about volume vs preasure sort of stuff like this to really get a good feel.

thanks

DP

The larger size of the lines should make absolutely no difference. What DOES make a difference is the ratio of the stroke volume of your MC piston to the volume displace by your caliper piston (pistons in your case). if your MC doesn't move enough fluid to throw all four of those pistons far enough to stop the Jeep, you'll need to look for an MC with a larger bore.

HTH,
Jake

when i bought my stainless lines they said that the smaller diameter hose will stiffin up my brakes and i thought what a crock of shit, just some fake selling point, but it did work and i got a stiffer pedal and better braking, just my $.02

Wouldn't smaller brake lines affect pedal pressure? Larger brake line would be , lighter brake pedal more sensitive brakes. Smaller brake line would be harder brake pedal less sensitive brakes?

(sensitive meaning, easier to lock up due to lighter pedal resistance when pushing brake fluid through a larger line)

hmmmmm

i keep thinking about this and i cant seem to really figure it out in my head.

i was thinking about like a water gun example....

you have those big super soakers..... say you have one with a small line w/ opening at the end pump it up and it shoots an initial 10 ft. now take the same gun put a bigger line in it and bigger hole pump it up and shoot it... now would it shoot the same initial 10ft or would it not shoot as far becasue of the larger line? (saying for instance its a controled environment and they had the same preasure and what not u know)

i would THINK they would be the same but im not sure.

dp

just an fyi guys.....

went over to autozone last night to rig up some lines and after fawkin with differernt fittings for over an hour we found that the INSIDE of the fitting on the rubber brake line is also threaded!!!!!! hey and guess what its the same size as a tj go figure right. just to make sure i got a good seal and all i got this lil flared fitting thing that screws in there and gives it a better fit.

i also found a short oh 8" or so rubber line with female ends that match the jeep (3/16) i picked up a couple of those and all the other stuff. The plan is to run hard line down the upper control arm and run rubber from the frame to the control arm and from the control arm to the T on the axle tube. shouldnt have any stress points and ill be able to put the suspesion in any sort of flex and not worry about lines being too short or getting caught in something. Ill post pics when i rig it all up tonight and ill get the part number for the lines if anyone wants them.

Like YJ_Swamper said, smaller diameter lines will make your pedal need to move less to stop you. However, you will have less ...resolution...in your pedal. I would think that ideally, you would want lines which allow a decent amount of pedal movement, with action ranging from barely slowing you to full lock up. The pedal travel distance between the two extremes will be effected only by the size of the master cylinder and the line diameter. I know this doesn't tell you what size to use, but I'd probably go with a similar size to those used on the donor trucks.

Reed

Originally posted by baylorboy
Like YJ_Swamper said, smaller diameter lines will make your pedal need to move less to stop you. However, you will have less ...resolution...in your pedal. I would think that ideally, you would want lines which allow a decent amount of pedal movement, with action ranging from barely slowing you to full lock up. The pedal travel distance between the two extremes will be effected only by the size of the master cylinder and the line diameter. I know this doesn't tell you what size to use, but I'd probably go with a similar size to those used on the donor trucks.

Reed

Wrong.

It doesn't matter how much volume is in the hose. The distance the pedal moves is solely dependent upon the ratio of the volume of your MC bore to the combined volume of your wheel cylinders or caliper cylinders (depending on whether you're talking about the front or rear system). Think about it: As the system functions, he volume of the hose never changes; just the volume(s) of the cylinders. (more on this in a second.)

That said, in the real world, the volume of the flexible hoses in a brake system DOES change, but (unless your lines are old, worn-out rubber ones) the change is very, very slight. They expand a little whenever the brake system is pressurized. I'd imagine that, the bigger the hose is, the more expansion you'll get because there is more inner surface area for the pressure to act upon and wider sections of rubber to stretch. Still, the difference would not be very noticeable between two purpose-engineered brake lines of different diameters. SS brakelines give a little 'tighter' feel because they expand a bit less because of the stainless steel braiding contaning this expansion a little better than the nylon webbing in rubber brake lines.


HTH,
Jake

Jake
- Good point. I forgot that in the end, the calipers and fittings would be the same size. My bad.

Reed

you can also take into consideration the fact that brake fluid is very slightly compressable so a hose with larger volume would feel a little "softer" at the pedal sense there is more fluid to compress. Take this and what Jakesteramalamajama stated and you may see a slight differance. Also the plan of hardlines down the control arms sounds pimp.

I know this doesn't help your situation, but it is along the same lines, ha, lines, funny, anyway, many years ago a dimwitted buddy of mine kept breaking front brake hoses on his Chevy pickup, so he went to a hydralic hose shop and had some huge aircraft hoses built. Bad, bad, bad, bad idea, the hoses worked for the first two stops, but they swelled so much under pressure that the third stop was almost fatal. You could actually watch the line bulge when he pushed the pedal, and contract when he let off. No matter what hoses you use, make sure they are approved for automotive brake fluid and pressures.

Jakster got part of it . . . The bigger the flex line the more swell, hence a possibly spongy pedal. That's why you very seldom see brake line that's bigger than 3/16" I.D. or AN3. But wait - There's more!

Line pressure will remain essentially constant throughout the system because the system is closed. So, not withstanding equalizers or regulators, if you have 750 PSIG at the master cylinder you will have very close to 750 PSIG at the wheel cylinders. Since there is almost no flow in a brake system, line pressure losses will be negligible.


There can be other issues such as master cylinder to wheel cylinder displacement ratios but that's a different can of worms.

crusher


yeah i think you nailed it. i was thinking about it more and more then looking at the fittings themselves all the holes are TINY....like the banjo bolts and such so there really isnt any benefit to running bigger lines. Thanks for putting it all into perspective for me guys it all makes sense now!

Common brake tubing is available in diameters from 1/8" through 3/8". Most oem cars today use 3/16. smaller tubing is stiffer and lighter and easier to bend. Larger tubing has less resistance to fluid movement and is less prone to to damage during handling. The 3/16 is a compromise arrived at after years of experieince - I recommend you use it. Not to mention, it's common - whcih can be important.

As other have mentioned, in all practical terms, the size from 1/8 to 3/8 isn;t going to make any real noticable difference hydraulicaly speaking...you're sure not going to improve your brakes any by changing size of the tubing. So use what is cheap, available, and easy to work with.