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I'm doing the routing path for my brake lines. My donor had 4-wheel disk brakes, and I'm using those.

I know if the master cylinder ends up below the front disk caliper (likely in my case) that you need a 2-lb valve in your front line to hold some pressure and stop fluid from draining, and I'm counting on that in my plan. Won't the rear line need the same 2-lb valve because it's a disk caliper?

To keep the rear brake line away from rotating parts on the drive line, it is desirable that my rear line climbs up about 12-14 inches before coming back down to the rear calipers. I've sketched out an exaggerated path in red in the photo below. It's not literally the intended path, but does illustrate the rise and fall that could happen. It is desirable that the single line exit at the top, rear of my transmission tunnel to avoid possible contact with the live rear axle moving up or down or laterally. My tunnel is very narrow at the rear.

Is this kind of up-and-down change in altitude OK with brake lines?


Any help would be appreciated.

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886

I would keep them as low as possible on the chassis. You really want the highest point to be the reservoir so it will naturally bleed itself. The next highest points should be the calipers for manual bleeding. I installed my bias adjuster high up for easy adjustment, I am sure it was constantly full of air. Now it, and all the lines are against the floor of the chassis and I don't have any issue with the brakes.

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2015 & 2016 EMod Florida State Autocross Champion
2013 & 2014 DSP Florida State Autocross Champion

Scrap Metal Build Log viewtopic.php?f=35&t=14558

What are you using for master cylinders?

As long as the reservoir is the highest point (not the cylinder), you're fine.

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-Andrew
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Youtube

It's not textbook, but you should be fine with that routing. When bleeding you move fluid fast enough to push the air out before it has a chance to creep back up to the high point in the line. Yes, you will want another one-way valve for the rear brakes.

Approximately even length lines after the tees is also good. Probably would never notice the difference, but it can affect braking performance.


Cheers.

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Build log: viewtopic.php?t=9291

I don't think you want those pressure holder thingies at all. I'm not used to seeing those on race cars. I don't think they are even intended for disk brakes. My formula cars spends years sitting on saw horses and fluid doesn't drain out of the disks calipers. They would have to have leaky seals to do that.

You don't want extra stuff in your brake plumbing, more joints etc. Plus how would the pads pull back from the disks by the caliper seals with 2 lbs. of pressure on the lines? I would also avoid extra ups and downs on the lines if you can, but you do what you have to.

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Marcus Barrow - Car9 an open design community supported sports car for home builders!
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I crewed on a Dekon Monza at the Daytona 24 in 1984. When building the car, the crew chief installed a vacuum line to the brake reservoirs through a ball valve in the cockpit. When the car would come in for a brake pad change, the driver would open the valve when the car came to a full stop. This would fully retract the pistons, allowing the new, thicker pads to be inserted easily. The important thing was to make sure the driver closed it prior to departing the pits! I have heard of installing a low pressure valve as described but once you are underway and have applied the brakes a few times, the heat of braking causes enough thermal expansion of the pads and metal components as well as the fluid. Any pedal lag on the track can only be related to air in the fluid or heat issues. Brake temps will actually rise on slow laps as the temperature rise takes a few minutes after a heavy application.

You could do this. It would be shorter route and completely along the floor. The Master being the highest point followed by the calipers.

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2015 & 2016 EMod Florida State Autocross Champion
2013 & 2014 DSP Florida State Autocross Champion

Scrap Metal Build Log viewtopic.php?f=35&t=14558

I concur.

I also question how brake fluid can leak back to the mc from the calipers when its a closed system. Where would the air come from inside the caliper piston cavity to displace the brake fluid thats departing the cavity? Air bubbles would have to travel from the reservoir downwards into the mc bore, past the mc piston, then through the lines to the piston cavity - I think not.

Here's another way I'll explain it. Get a glass of water and a drinking straw. Suck up water into the straw, then cap the straw with your tongue while the straw is in the glass of water. Do you see air bubbles going through the water into the straw and displacing the water in the straw - no, it's a closed system.

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Perry

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Thanks everyone for responding. I'm in a rush this morning, so I'll just acknowledge you all collectively.

It sounds like the 2-lb one-way valve isn't something everyone wants to use. However I've seen it recommended in a couple of places including Wilwood (my component supplier) and also, I think, in Fred Puhn's book, which is what I used to do all the brake calculations. I'm not much of a brake person right now. That's likely to change when I get my car built and have to test it [LOL]. It's easier to include them and delete them later rather than add them in after the build.

I'll be using the remote reservoirs for the master cylinders, so it sounds like if I keep the highest point of the rear brake line run just below them, I'll be OK. Thank you all for that.

Paul, I'm with you on the preference for keeping things low. I don't want the lines inside the car however because I'm going to have rugs and upholstery. If there was a leak in the cabin, I'd never get the stink out. I have been considering running the rear line under the car on the undertray. I'd have to shield it by running the line in some kind of metal half round or channel, but it's very appealing because of its simplicity.

To avoid the worst hazards (if I run it inside the tunnel), I have to steer clear of the bellhousing (explosive clutch failure), transmission mount (pinching brake tube on eng/trans install) and the drive shaft/U-joints (for obvious reasons) and the live axle pumpkin (because of my very narrow tunnel). Running under the car in armor has a lot of appeal. I have 17" wheels and low profile tires, so I don't think scraping after tire failure is likely, but scraping on speed bumps is a fair possibility.

Thanks again for the responses.

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886

I went through the transmission tunnel. Usually the tunnel is taller than is is wide which leaves lots of room in the bottom for fuel, brakes and electrical. You could also add a plate above the tubes and wire to make a channel, which would be isolated from the drive shaft. You should be able to get everything below the transmission mount. Mine now sit below the mount and there is plenty of space for everything.

I would not worry about having them near the bell housing. If the bell housing fails you have bigger things to worry about and are going to have to pull the engine anyway. Replacing the brake lines will add 20 minutes to a long job. Speaking of bell housing exploding get yourself one of these http://www.jegs.com/i/JEGS-Performance- ... 0/10002/-1 mine only weighs about 4 lbs and is easy to fit. I'd recommend a drive shaft hoop or two also if you don't them already. The drive shaft is the thing that scares me the most.

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2015 & 2016 EMod Florida State Autocross Champion
2013 & 2014 DSP Florida State Autocross Champion

Scrap Metal Build Log viewtopic.php?f=35&t=14558

@wrightcomputing
Thanks for the additional input. I posted my latest ideas to my build log, Paul. That ballistic blanket is an interesting idea. I'll have to learn more about it.

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886

Regarding residual pressure valves: I'm pretty sure "fluid leaking back into the M/C" is one of those misnomers like "backpressure gives you torque". However, there are some very good reasons why you want a RPV (when needed):

-The piston seals are designed in such a way to pull the pistons back, away from the rotors, when pressure is released. If the pistons are pulled back too far your pedal will be spongy and/or pedal height is erratic. I've installed rebuilt calipers that retract too far and it ranges from crappy pedal to undrivable. The RPV helps prevent this.

-When the pistons get pushed back by the runout/warp of the rotors, the velocity can push the pistons back further than ideal (again, spongy pedal and erratic pedal height).

-The velocity of the fluid on push back can cause negative pressure on the system. Potentially allowing air to be pulled past seals, or the fluid to boil. The RPV prevents this.

-With a RPV, any small leak/weep of the system will result in fluid going out rather than air going in. This is a good thing.

Note: I would have to dig up some books to confirm that this is all fully accurate, but I think the gist of it is correct.

Cheers.

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Build log: viewtopic.php?t=9291

I'd go without the RPVs first and see how it does. Odds are you don't need them.

Depending on which master cylinder you choose, it may come with all of the stuff to do a remote reservoir should you put the master cylinders down low. I'd go this route first.

_________________
-Andrew
Build Log
Youtube

@a.moore

Thanks for the input, Andrew.

The MCs I've selected are from Wilwood and they can be had (or changed when in place) with either an attached reservoir, or a remote one. I'm leaning towards remote, but still have some engine compartment packaging issues to work through, so I'm not positive as yet.

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886

I'm at the same stage. I bought residual valves for both the front disc & rear drum brake lines. I'm using all Wilwood cylinders, and they strongly recommend the use of residual valves with their master cylinders if the master cylinder bore is below the top of the caliper (for discs) or the wheel cylinders (for drums). In my car, this is definitely the case - my M/C's are at floor level, far below my calipers & wheel cylinders.

My thinking is that Wilwood employs some of the best brake system engineers anywhere, so they sure know a lot more about the subject than I ever will. If their engineers feel that safe operation requires the use of residual valves, I'm going to go with their recommendation. It can't hurt, but the lack of them (if the engineers turn out to be right) certainly could!

Just my $.02' worth...

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