Tell me why

[JeepsAndGuns]

I was thinking the other day and I was wondering why for the rear the brake line doesnt split untill it is on the axle, makeing only one rubber hose going from the axle to the frame. But on the front, the line splits after it leaves the m.s. and then two rubber hoses (one on either side)run from the frame to the axle. Why not make it the same as the rear? Only one hose running from the frame to the axle would make more sense to me. I was thinking about running the brake lines just like they are on my rearend, Just one hose from the axle to the frame, then a hard line running the length of the axle, then the rubber hoses mounted to a custom bracket welded to the axle leaving enough slack in the line for steering. Is there somthing wrong with doing this? as I have never seen any 4wheel drive truck or Jeep or any striaght axle rig with their brakes like that. Whats wrong with this setup? I can see the need on cars or a truck that has IFS. but for a solid axle I dont see why.

[Rogue]

i don't see why you can't or why they didn't

[porkchop]

Check outt his site http://auto.howstuffworks.com/framed.htm?parent=question453.htm&url=http://www.icpeducational.com/auto101/braketext.html
If you can't find it there then just go to www.howstuffworks.com (http://www.howstuffworks.com) and do a search.

My thoughts would be that the rear brakes are drums and they do not require as much pressure to operate. So the line does not need to be split. The same reason that the front brakes have the larger resivor in the master cylinder. Just my guess.

[krob725]

cj2a's were built that way

[jeepguzzi]

I think that you have flexible lines on the front because you have disc brakes and the calipers need to move. Also, I think the left and right fronts need to be on different circuits in case of a leak, you still have brakes.

[Hammer]

Safety and backup in case of line failure. On the rear, it only takes one failure to loose all rear brakes. But you don't want that on the front.

[LRRH]

also..the line running to the rear is larger than the individual lines in the front.

[The Anti-Chrysler]

Well the front is still one line up to the proportioning valve, so if one front line goes, then I would think both front brakes are a gonner.

[FSJ Thing]

It's probably just one of those "Why are railroad ties 58 inches wide?" type things. We'll probably never know. Personally, I'm thinking it's because the knuckles in the front rotate relative to the axle tubes, where as the rear doesn't.

[Hammer]

One line fromthe MC to the proportioning valve. If that fails, the rear works. But that part is not the typical point of failure. Rubber hoses, especially ones that are subject to constant flex/movement, and the seperate hoses are after the proportioning valve, so they are kept seperate (if the valve is working correctly. I think).

[tgreese]

Fewer rubber hoses with the stock setup. You always need a flexible line from the wheel to the axle or frame to allow the front wheels to steer. To go from the axle to the frame (rather than the hub to the frame) you need an additional rubber line from the axle to the frame. I'd say it's cheaper to run two flexible lines to the front wheels rather than three.

[Nobby]

if you look at cross section of a proportioning valve the ports for front left and right are common. see this link

http://www.hunter.com/pub/undercar/2690T/2690T.HTM

So there is no advantage here with regard to breaking one of the front lines after the P.V. that is pressure will still be lost to the other front line. The only safety given with regard to breaking lines is the fact as already mentioned the front and rear have seperate resevoirs and that the front is larger in volume so you have a little more oil to go for a minor leak.

You of course need flexible hoses for each front wheel because as mentioned already the hubs move in all directions.

As to why no single line from the P.V. to the front axle and then a T well if you think about it you may need to then use 3 flex hoses as Tgreese said. One to the axle and then one at each hub. Unless of course you T right after the P.V. and then run as rest of line as is now.

Seems to me its easier and gives less joints and pipe sections if you incorperate the T in the P.V. as is. Makes for the simplest and tested method.

[ November 13, 2003, 12:45 PM: Message edited by: Nobby ]

[JeepsAndGuns]

Having two rubber hoses for the front rather than three is the only reason I could think of too. But what if you used the steel braded ones?

[oldyellowwagoneer]

Actually alot of dodges do only have one brake line going to the front axle. When we put a dodge D60 in a cherokee chief of my friends we used the dodge master cylinder and proportioning valve. The brake line was ran down in the center and we didn't have to use a very long one to do it. Dennis

[madison]

Nobby said mostly what i was going to say, the front has to deal with the brake caliper moving, so the rubber is there to move and not break the line.
braided lines is just like rubber lines they flex, but they are tougher and last long.

also another reason for two lines in front and one in rear is because of pressure. the drums don't need that much pressure so it runs off of a single large line. the front needs the pressure so they(factory) put two small lines going to the front to create more pressure for the disc to work properly.

Got to love physic!!!!

[madison]

also if some can get me a pic of this one front brake line on this d60 dodge i would appreciate it. i never seen one yet and i want to see it!!!

i would think that this front end still has the rubber lines going to the brake calipers and what i think is they use the one line to a "t" and got real small lines on it to make pressure??

[Bob Barry]

Originally posted by madison:
also if some can get me a pic of this one front brake line on this d60 dodge i would appreciate it. i never seen one yet and i want to see it!!!

i would think that this front end still has the rubber lines going to the brake calipers and what i think is they use the one line to a "t" and got real small lines on it to make pressure??That's exactly how it is. I am running a front Dodge D60, and will just be running a single line down to the flex-hose from the frame to the axle. It "T"'s on the axle, then runs to rubber lines that attach to the calipers. I plan on using the rear hose from a '78 Ford F250, which is 23" long, and just running it down from the inside of the frame-rail to the pumpkin. That way, I won't have to worry about over-extending the hose (with the Waggy springs, I have to have the bumper of the truck in the air above my head with an engine-hoise before the axle actually starts to lift the tire off the ground, so there's quite a bit of travel that the hose has to accomodate.).

[jode]

Physics !?!!??? :confused: -
IIRC, in physics, pressure is independent of volume or tubing diameter in a situation like brake lines. The only reason you would need two lines over one would be to allow a greater flow with less resistance if the front pistons needed more fluid flow. The exact same pressure will transmit through one line that is .00001 mm thick as one that is 2’ thick…smaller lines don’t make greater pressure. That is the WHOLE concept of hydraulics!
I think it is fairly clear that OEM, two lines is cheaper than three (as with the Dodge).

[JeepsAndGuns]

So would there be any danger or brake preformance loss if I did the one hose up front and just use a steel braded hose made for the rear? And steel braded ones for the caliper hoses too? Makes sense to me.

[oldyellowwagoneer]

Originally posted by JeepsAndGuns:
So would there be any danger or brake preformance loss if I did the one hose up front and just use a steel braded hose made for the rear? And steel braded ones for the caliper hoses too? Makes sense to me.That would work just fine. Dennis

[Bobbo]

Sounds like a bunch of work for not any gain to me. Some things are better left stock. I would say its all set up to work like its all ready set up. If you change line lengths/number of lines and t locations, it could alter the proportioning of the brakes and/or the pressure the calipers were designed for. The master cylinder my put to much pressure, or not enough. I'm not saying it can't be done, but with all the aftermarket brake companys out there, it would be better to use their R&D for your advantage. I think you would waste more time than you would want to. Just my opinion!

[madison]

jode

big tubes means larger volume lower pressure,
smaller tubes means smaller volume higher pressure.

take this in mind when u run a garden hose without the nozzle on it is not high in pressure but flows more water,
but put that nozzle on and it is higher in pressure but not as much water. this is based on physic.

to generate the pressure it has to be passed through the smaller lines.

how do u think that hydro boost work better then regular power booster, it generates more pressure!!!!

and the piston on the caliper can not be pushed out by low pressure, atleast not enough to stop our beast. so it has to create more pressure!!

[jode]

No no no!
This is hydraulics: Whatever psi is applied to one part of a hydraulic system is transferred eqaully to all the other parts of the hydraulic system. That is it!
The way a brake system works is this:
Mechanically, your foot has X amount of pressure, we'll say 20 lbs. You apply that 20 lbs to the pedal. The pedal is attached to the hydraulic system in a manner so that your 20 lbs is applied to a plunger of say .5" What that mean is that you just applied 20 pounds of pressure to 1/2 of a square inch. Because of that, the pressure with in the system will be 40 lbs per square inch. That hydraulic pressure is the same on ALL surfaces within the hydraulic system. So what happens at the other side, is that you use a piston that has a plunger with a surface area of say, 4 square inches. So you 40psi is applied to 4 square inches. Do tha math on that and you find that the final mechanical pressure that is applied to that plunger at the caliper is 40psi X 4si = 160 lbs pushing on that brake pad!
And that my friend, is how a brake works. Of course, modern brakse have things like vacuum assist, etc. but the statement about small tubes building pressure is bunk.

However - here is why small tubes are better. If you reference the hydaulic concept again, you'll note that the pressure within the brake lines is 40 psi. So you need something that has thick walls in comparison to its inner diameter (surface area). So the small tubes are ideal - there is limited surface area, and maximum wall thickness to diameter. Also, due to the hydraulic concept, the volume of fl;uid within the tube is irrelevant to its function, so using a thicker line would be pointless.

[jode]

Still think I'm wrong?

Have a look at THIS! (http://auto.howstuffworks.com/brake3.htm)

[jode]

BTW, your hose example is good, but is a totally different situation than brakes. With the hose example, you are talking about "Flow rate" - a totally separate and unrelated subject...

In a hose, what you are dealing with is a constant flow that is created by a difference in pressure. In other words, the pressure behind the water is greater than atmospheric pressure, and that is why the water comes out of the end of the hose. Say there is 60 psi behind the water pushing it out. It will flow pretty good. Then you plug it half way...it will APPEAR to flow faster and at a higher pressure...this is also a physics law as you stated, but it is a different one.
This one has to do with the fact that when a fluid flows, the rate of flow is determinate on the diameter of the tube it is flowing through. So if a hose drops from a 1" diameter, to a 1/2" diameter, the fluid in the 1/2" tube has to flow like twice as fast as the water in the 1" tube. However, it doesn't Create pressure....the only reason the pressure would be higher in the 1" tube is because the water can't instantaneously increase its velocity due to another physics law we like to call momentum.
However, in a brake system, neither end is open to the atmosphere (I hope ;) ) so this whole hose thing has NOTHING to do with it.

OK, so it does have a slight bit to do with it...in fact, the smaller tube will cause the fluid to move more rapidly (Flow=volume/time) and if you apply Bernoullis to that, you would see that a smaller tube will, in fact, DECREASE the pressure! But that will only be during the time fluid is flowing - obviously, the pressure would come back up as soon as the fluid stopped moving.

[oldyellowwagoneer]

To end this argument; In this example it's no difference between the two since the master cylinder has only one line coming out of it it doesn't matter whether it splits off at the proportioning valve or at the tee on the diff. The proportioning valve does not limit the front brakes but rather the rears so it doesn't matter to it if it has one line coming out of it(dodge) or two(jeep,chevy). You do however need to make sure the volume to the point where they split is sufficient, that's why the dodge line coming out of the proportioning valve is the same size as the one going in. On the jeep type system the volume of the two lines coming out combined are about the same as the one line going in or pretty close to it(always the same or less volume since if it were higher the flow would be less resulting in lower pressure at the caliper).

[JeepsAndGuns]

The reason I thought about this is because when you run a big and/or flexy lift, you have to have longer hoses. when the hoses are at the end of the axle coming from the frame they have to have enough slack in them to be able to let the axle fully droop when your flexin. So when you are not flexin you have a lot of slack that could rub up aganst somthing. If you run just one hose in the center of the axle you only have to have enough slack to let the springs droop. because the center wont droop down as mutch as the ends of the axle will. as for the two smaller lines equiling the the size of the one before the split, just run the larger one up to the hose going to the axle and then run a hose that is the same or close to the same size. then when it splits on the axle run the two smaller ones.

[oldyellowwagoneer]

Originally posted by JeepsAndGuns:
......... If you run just one hose in the center of the axle you only have to have enough slack to let the springs droop. because the center wont droop down as mutch as the ends of the axle will. as for the two smaller lines equiling the the size of the one before the split, just run the larger one up to the hose going to the axle and then run a hose that is the same or close to the same size. then when it splits on the axle run the two smaller ones.Thats precisely what I'm saying. Dennis

[madison]

i would think that when u push the same amount of fluid into a big or small line, the smaller one will have the most pressure cause of the area it has to be pushed into?? so therefore it would have more pressure to push that piston in the caliper then the larger line would??

but what do i know i am just studying to be a mechanical engineering!!!

i also think of compression in this situation, like a piston and head compression the smaller the more pressure it has. the larger the less pressure it has.
also the poportion valve is design to change the pressure so the rear don't lockup.

[oldyellowwagoneer]

Originally posted by madison:
i would think that when u push the same amount of fluid into a big or small line, the smaller one will have the most pressure cause of the area it has to be pushed into?? so therefore it would have more pressure to push that piston in the caliper then the larger line would??

( Then again you can also look at the smaller line as a restriction since it necks down from the bigger line and then opens back up in the caliper, in whick case you would have a pressure drop. Thats a simple rule of hydraulics-restriction increases pressure but only before the restriction not behind it.)

but what do i know i am just studying to be a mechanical engineering!!!( you've got more patience than me. Good luck on that I can't stand the homework.)

i also think of compression in this situation, like a piston and head compression the smaller the more pressure it has. the larger the less pressure it has.
(not true if your talking about smaller piston diameters having more pressure on the surface than larger ones, As long as the stroke is the same they will have the same p.s.i pressure, with the larger one having a larger total force on it, If your talking about head chamber volume then yes the smaller chamber will have a higher compression ratio.As far as brakes go this would mean that the smaller caliper piston would have more pressure on it per p.s.i. but not always more force total. Simply put the bigger the piston the more volume you need.)

also the poportion valve is design to change the pressure so the rear don't lockup.
( I agree with this and never said otherwise but this topic was about front brakes so I didn,t go into that since I didnt want to confuse the topic at hand.) Gee I'm kinda being a windbag today aren't I? Dennis

[madison]

i am thinking of the pistons related to compression. 9:1 is a lower pressure them 12:1.
it squeezes a large amount of air in to a smaller pocket.

since brake fliud is supposely non compressable, in this situation the piston wouldn't move cause they can't move out.

with non compressable fliud if u have more volume the piston (in the caliper) would move out with more pressure.
so the smaller line will restrict the flow causing a lost of pressure till the fliud is passed by. is this what ya'll saying??