Specialty Brake Lines

[TheMonkey]

The way my front discs set up, what I really need is a 12" stainless braided brake line with -3 AN fittings on both sides, and 90° elbows both sides.



Best I have found has an elbow on only one side, and straight on the other. I tried it, and it just gets too bendy with this.

Anyone have suggestion on where to find a double elbow brake line?

[JRouche]

Does your line have a -3 fitting on both ends. If so you can use an elbow fitting on each end? I just bought some elbows today. 5 bucks a piece from hoseman. I needed 3/16" tube (-3 AN) on one end and 1/8" pipe on the other, both male. An I missing something?? JR

[TheMonkey]

JR:

yes, -3 both sides.

you are right, in this case, i could use an elbow bulkhead fitting instead of straight.

but... isn't this a pretty sharp turn for a brake line (see first pic)? if i could find the 90° elbow on the the brake line in second pic on both ends. the turn just seems a bit less violent.

[Apogee]

While I would prefer a sweep 90 in most circumstances given the choice, it doesn't tend to work well to have two fittings on one hose assembly that have a definite timing orientation. There is remarkably little fluid flow in most brake systems, so don't let the tight elbows scare you too much. That's essentially what you've got at your T-fitting at the rear axle.

By having two 90 degree fittings on a hose assembly, you're forcing the relative orientation of the hose ends to one another. In order to assemble such a hose, we would need to know what timing you wanted the fittings relative to each other so that they could be assembled and then installed. We can do this, but we don't usually sell such a hose because people don't generally specify the proper timing and then the hose gets torqued and kinked and won't route properly. It's a lot easier to leave one end a non-directional fitting like a straight AN so that everything installs easier. This is true for male threaded fittings as well for similar reasons.

Tobin
KORE3

[TheMonkey]

Thanks for the explanation.

I was just thinking about your comment about how little fluid travels. Tell me if I'm doing my math wrong.....

bore of MC = 1", which is an area of .785"
bore of brake line = 3/16", which is an area of .0276"

for every inch of stroke at MC, fluid will travel 28.4 times that length. so, push pedal down for a stroke at MC of 1.5", that is 32" of fluid travel in the brake lines. that seems like a lot.

oh wait... more than one brake line.... would you divide that by 4 (each corner)? i guess 8" of travel does not seem like much. anyhow, prob over-thinking it again, and should just put in the elbow bulkheads that can be clocked any direction. thx.

[Apogee]

Well you are doing your math wrong since you didn't account for the wall thickness of the tubing, but you've got the right idea. There's also a volume ratio designed into the MC, but we don't need to get into that for this.

I won't say that you're not over thinking it...but better that than the alternative. It's also important to remember that just because you're stroking the MC 1" and the fluid is theoretically incompressible, that does not mean that it all correlates to volumetric flow, at least not in the way you described it. Every component in a brake system has a certain amount of compliance associated with it as it expands due to the pressure of the brake fluid. This compliance comprises more volume than you might think, hence the benefit of braided stainless hoses versus rubber and 3/16" hard line versus 1/4". Some components contribute very little and others contirbute significantly more to the total compliance of a system, but they all contribute something.

Once the caliper pistons have pushed the pads into full contact with the rotors, any pedal movement is entirely caused by compliance in the system. Smaller bore MC's make more pressure and therefore feel "spongier" due to the higher system pressures. The opposite is true for larger bore MC's.

Tobin
KORE3

[TheMonkey]

okay, as long as i'm encouraged to keep thinking about it:

you're right, diameter should be calc'd from ID. ID of my -3 tube is 0.1295" which would be a ratio of almost 60x, and with volume ratio, it would presumably have a heavier bias of that ratio to the front. intuitively, that seems like a lot of fluid flow through the front elbows.

but, what you are saying, is that only a little bit of pedal stroke actually contacts the pads, and the rest is 'compliance' in the system. just today, a guy with experience was telling me how much of a difference stainless braided brake lines will harden up my pedal.

is the 'compliance' the reason for your original comment: "There is remarkably little fluid flow in most brake systems" ?

[MonzaRacer]

Well most people dont also understand that your caliper piston will actually only move 0.010 or less if my measurements were right, wheel cylinders it depends on brake shoe adjustment/flex, but honestly in disc/disc you more raising pressure exponentially and not really moving a lot of fluids, and if my silly head full of math gives me proper figures without thinking too hard your moving something like a teaspoon or less of fluid in what 5 to 8 inch length(just picking a point A start to point B )in milliseconds, your actually not moving the whole column of fluid the fluid in the tube near the line walls is nearly static, and the center of the fluid is rushing forward. think of it in your mind of when your cursor jumps from one spot to another.
Honestly after helping a fluid dynamics student, the movement is ridiculously small and fast as most of his work was on tempered glass tubes that mimicked brake line, and he was showing how the stuff moves, (he had food coloring in actual brake fluid. That elbow just doesnt restrict as much as you would think , on disc. On drums too many MAY cause issues unless using larger tubing(ie 1/4)

[Apogee]

...is the 'compliance' the reason for your original comment: "There is remarkably little fluid flow in most brake systems" ?

Yes, that's exactly what I meant in relation to the amount of pedal travel. When you apply the brakes, you should be able to feel the pads make contact with the rotors fairly early in the pedal stroke. The system is continuously full of fluid, so with the caliper pistons being the only moving parts, once they hit the rotors your system goes from moving fluid to then generating pressure. The only fluid flow from that point forward is directly related to the compliance of the parts in the system.

MonzaRacer gave a pretty good reference for perspective relating the actual volumetric requirements to a unit of measure we're all familiar with, the teaspoon. A C5 front caliper with 4.0 square inches of piston area requires .133 teaspoons of fluid to move the pistons .01 inch. For comparison, a 7/8" bore wheel cylinder has a comparitively small area of .6 square inches, but might stroke upwards of .25" or more, requiring as much or more volume as the front calipers.

As for braided stainless hoses, they're thousands of times less compliant than a reinforced rubber brake hose IIRC. Goodridge published a comparison at some point and for all intensive purposes, a braided stainless hose is much more similar to the hard lines than to a rubber hose with respect to compliance.

Tobin
KORE3