-2 for front brake lines

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Speedsport
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-2 for front brake lines

Post by Speedsport »

Anyone have success running -2 for front brakelines? I'm a little concerned about doing it with our drum brakes.
FV80
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Re: -2 for front brake lines

Post by FV80 »

Mike,
I would think it might add some delay - you'll be moving a LOT of fluid through a pretty small pipe. I have run into issues using -3 on a 6 foot run to the remote reservoir on a Penske and it moves a lot less fluid. However, I have not tried it.
FWIW,
Steve, FV80
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Mystique Racing
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Re: -2 for front brake lines

Post by Mystique Racing »

I see that some are using dash -4 lines for brakes. Any opinions or reasoning on -4?
Scott

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smsazzy
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Re: -2 for front brake lines

Post by smsazzy »

I run -2 on all 4 wheels. (-3 on the clutch) It is the only way to go. Much better pedal feel.

The fittings are a little pricey, but I was able to get what I needed through Jim at SR. You'll want to go with the -2/-3 fittings. They are a -3 end with -2 internals. I have part numbers somewhere.
Stephen Saslow
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Re: -2 for front brake lines

Post by FV80 »

Stephen,
Why would -2 provide a better pedal feel?? Seems to me that the larger the line is, the better the pedal feel. Of course I haven't tried it.. it just SEEMS that way to me :mrgreen:
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racing stuff
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Re: -2 for front brake lines

Post by racing stuff »

Stephen,
The reason for the better feel, is less fluid.
All fluids are compressable and the less you have inside the line, the firmer the pedal becomes.
-4 on brakes is not a very good idea, for a clutch it's OK.
Long lengths of "flex" brake line can also make the pedal "soft". All flexable lines expand, even teflon a small amount.
Tha's why it's best to make your long run to the rear brakes, or clutch that mater, in hard line.

-3 on brakes is the norm, even brake cylinders.

-2 we normally sell to those plumbing a brake caliper on a Formula Atlantic car and vehicles like that.
I'm not sure I would recommend it for actuating brake cylinders, but obviously some have done it.
Yes the fittings, and hose are more expensive.
Keith
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smsazzy
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Re: -2 for front brake lines

Post by smsazzy »

Keith hit the nail on the head. Less fluid to compress is the reason.

I, personally, feel that is even more critical in a brake system pushing wheel cylinders.

YMMV. :-)

Stephen
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Re: -2 for front brake lines

Post by jstoezel »

There must be a terminology gap/typo in the last 2 posts, my understanding is that at the pressures we're dealing with here, the brake fluid *will not* compress significantly. And this is why we use fluids to move the cylinders, not gas.
Last edited by jstoezel on March 1st, 2012, 2:43 pm, edited 1 time in total.
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Re: -2 for front brake lines

Post by BLS »

While fluids do compress, I don't think you can tell it at our pressures. Maybe the smaller line expands less...
Barry
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Speedsport
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Re: -2 for front brake lines

Post by Speedsport »

When looking at the -2 fittings, the hole for the fluid passage is incredibly small...my concern is what steve originally stated - there would be a bit of a delay in pushing the fluid through that opening. With disc brakes I don't think it's a big deal, but with the volume of fluid that needs to be moved for our drum brakes, I'm a bit concerned.

The I.D. of the -2 hose is probably fine, it's the fittings that are choke point. I didn't measure it, but I'd guess the ID of the -2 end I looked at was around .030" since it has to fit inside the ID of the hose. The -3 I'm guessing had 3-4 times the area of opening.
cendiv37
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Re: -2 for front brake lines

Post by cendiv37 »

Mike,
I think I agree with your concern, but I'm guessing it would only be a problem as the pedal goes down during a session (which is a real potential problem). With brakes adjusted up "tight" it would be an interesting calculation to determine which took more fluid to activate, 4 small diameter wheel cylinder pistons moving a "large" distance or 4 larger diameter caliper pistons moving a small distance.
Bruce
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Re: -2 for front brake lines

Post by AJP »

cendiv37 wrote:Mike,
I think I agree with your concern, but I'm guessing it would only be a problem as the pedal goes down during a session (which is a real potential problem). With brakes adjusted up "tight" it would be an interesting calculation to determine which took more fluid to activate, 4 small diameter wheel cylinder pistons moving a "large" distance or 4 larger diameter caliper pistons moving a small distance.

I was also thinking that would be an interesting calculation. I think one difference would be that the large diameter disc brake pistons are always "dragging" a bit or always really close to keeping the pads against the rotor.
I don't think we try or want to keep the shoes as tight to the drum. So we may need to move further but it's still one cylinder/wheel vs most calipers which have 2 cylinders.
I'm curious now.
First person to do the math gets a gold star.
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Re: -2 for front brake lines

Post by smsazzy »

Speedsport wrote:When looking at the -2 fittings, the hole for the fluid passage is incredibly small...my concern is what steve originally stated - there would be a bit of a delay in pushing the fluid through that opening. With disc brakes I don't think it's a big deal, but with the volume of fluid that needs to be moved for our drum brakes, I'm a bit concerned.

The I.D. of the -2 hose is probably fine, it's the fittings that are choke point. I didn't measure it, but I'd guess the ID of the -2 end I looked at was around .030" since it has to fit inside the ID of the hose. The -3 I'm guessing had 3-4 times the area of opening.
Mike - I ran all last season with -2 lines. There is no issue whatsoever. Whether it is worth the extra money is each individuals decision. I will always have -2 on my cars in the future.
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Re: -2 for front brake lines

Post by SR Racing »

-2 lines are fine especially with discs. With drums you just have to make sure you have them adjusted well. The only compression issue is the lines themselves. Pure Hydraulic brake fluid compression is so slight as to be NIL. Except DOT5 (Silicon) which can feel spongy. After bleeding the standard assumption is that there will be far less than 3% compression in volume of a break fluid. This is ONLY due to the few molecules of air still left in any system at high temps. You do not get brake fluid hot in a drum brake system. So for all practical purposes all compression (expansion) is in the lines themselves. (a -02 has quite a bit less surface area.) If you have a disc brake system (no pushback) with hard lines the pedal will be as hard as brick and you will feel NO compression at ANY foot pressure until a line bursts. :-)
brian
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Re: -2 for front brake lines

Post by brian »

Jim is correct, the only issue with larger brake lines is expansion. At drum pressures, it's virtually a non issue. For all intents and purposes, fluids do not compress. Ever try to kick over a motor that has a cylinder filled with fuel or water? The dispacement of fluid is dependent on the relative piston sizes between master and wheel. You can ratio the differences and either get less travel at the pedal, which makes it harder to push and less sensitive to the driver, or allow more travel and make the pedal easier to modulate to avoid lockup and skidding. I'm no engineer but I was taught, by a Bendix brake engineer, that one cubic inch of fluid displacement at the master, will equal one cubic inch of of fluid displacement at the wheel cylinder. While there may be a RATE of displacement issue, line size will not effect that relationship. Improperly bled brakes that contain air negates everything I've said.
The above post is for reference only and your results may vary. This post is not intended to reflect the views or opinions of SCCA and should not be considered an analysis or opinion of the rules written in the GCR.
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Re: -2 for front brake lines

Post by BLS »

While there may be a RATE of displacement issue
Brian, I think that is the question. Will the -2 line slow down the pressure change due to the friction in the tubing? If it is negligible, then I don't see why -2 wouldn't be better. It's only effect would be to reduce the expansion value. Personally, I can't imagine I could detect the difference in -2 and -3 line. Maybe others can.
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Re: -2 for front brake lines

Post by jpetillo »

Brian, you're right about the fluid displacement at the master cylinder being the same as that in the wheel cylinders, and the rate would be identical if it's incompressible. BLS, about friction, it's a good question. The brake fluid along the surface of the brake line walls does not move due to boundary layer affects, and so causes drag. That boundary layer up against the tube wall is the same thickness in a smaller or larger diameter brake line, and the farther away from the wall you get the freer the flow. So a larger diameter line will have less drag since the amount of fluid far away from the wall is much more and will have freer flow, and it doesn't have to move as fast since it's a fatter line - you win twice in that regard. Now,whether that drag is enough to feel in terms of a pressure difference causing resistance while putting on the brakes, I don't know. If it does, it would work both ways and slow down the release of the brakes as well. It's probably not that hard to figure out. I think I'd be more concerned with the size of the orifices in the fittings. John
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Re: -2 for front brake lines

Post by smsazzy »

You are way over thinking it. I won the NorPac division last year with -2. They work fine.
Stephen Saslow
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Re: -2 for front brake lines

Post by jpetillo »

Not much thinking - more like just typing! I didn't say I thought it was a problem or not, I was just explaining one way that drag occurs with fluids through lines - in case someone cared. John
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Re: -2 for front brake lines

Post by BLS »

Stephen, how much flex line do you use? All flex or a combination of hard line with shorter flex? Just curious.
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Re: -2 for front brake lines

Post by brian »

Thinking is cheaper than paying a premium for something we don't need. :lol:
The above post is for reference only and your results may vary. This post is not intended to reflect the views or opinions of SCCA and should not be considered an analysis or opinion of the rules written in the GCR.
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Re: -2 for front brake lines

Post by smsazzy »

All flex line.
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Re: -2 for front brake lines

Post by BLS »

Stephen, thanks.
Barry
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