Brake Indicator Switch and Brake System Balance

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heirfaus
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Re: Brake Indicator Switch and Brake System Balance

Postby heirfaus » 14 Apr 2010 23:01

510rob wrote:Review Pascal's law. Also, consider that pressure is a resistance to flow. Lastly, try not to confuse pressure and force.



From Wiki:

Pascal's law: Pressure on a confined fluid is transmitted undiminished and acts with equal force on equal areas and at 90 degrees to the container wall.

This is what I was trying to say with the "1 inch, .1 lines." so it shouldn't matter if the shuttle valve has moved because no matter how small the line is, the end user, being the caliper, is still the same size (in my example above) and that means that we still have the same "undeminished" pressure on "equal areas" (the calipers in my example) in a "confined fluid". right? :?
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Re: Brake Indicator Switch and Brake System Balance

Postby Byron510 » 01 May 2010 19:18

OK, time to relight this thread! :D

So I was working on my shop mate’s vintage race 510, and we were plumbing brake lines. Low and behold, I got to measure everything.

Stock Datsun brake tubing ID = 3.2mm = (8.042 mm square cross section)
Brass block "restrictor" above transmission = 2.4mm (4.524 mm square cross section)
Inlet to stock Datsun rear wheel cylinders = 3.0mm (7.069 mm square cross section)

We were re-plumbing the lines in the car. Since the entire rear drive train was out, we felt it was time to replace the original brake lines, as they didn't look very good. Just for interest sake, the ID of the AFTERMARKET brake tubing is 2.6mm (5.309 mm square cross section)! So the restrictor, as it were, will not be used and the brake line will now go through the cockpit from the firewall to the rear seat area.

After doing the math; the 2.4 mm brass block orifice has barely over half the cross sectional area of the stock brake line. However the real story is the inlet of the rear wheel cylinder. The brass block orifice is about 63% the size of the wheel cylinder orifice.

Just food for thought.
Of course all you guys running rear discs have other issues and fittings.
Keeping in mind that the actual flow through the rear brake line at application is nearly irrelevant, making me think that the orifice does little, if anything at all. I’ve had some experience with hydraulic systems when working with the Navy. In a stock 510, my feeling is that by the time you stab the brakes in a panic stop, the hydraulic system will have equalized in pressure (fron t to rear) long before the spongy front suspension would hit full compression, making this "restrictor" irrelevant in the overall system dynamics, at least in regards to helping stop the rear wheels from locking. So, I honestly think we are back to square one. There is no proportioning valve in a PL150 – we know this, and the "restrictor" isn't much of a restriction when you think about how little fluid is actually traveling through the line.

Disclaimer:
The car in question is a 69 model 2 dr, and I’m sure it was the original part. However, this has been a race car since the mid 70’s, and it has been in the very capable hands of Andy at Specialty Engineering for that time. So, anything could have been changed. However I still have the fittings that came out of the Bronze, and I will one day make a point of checking them, as well as any other brass block orifice I can get my hands on, just to make this legitimate and not another internet myth. :roll:

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Re: Brake Indicator Switch and Brake System Balance

Postby bertvorgon » 02 May 2010 07:08

Thanks for checking that out Byron. That "restrictor" is really not at all. The way Jeff had said it, I thought it was a pin hole! 2.4 MM is like what, a .093" hole?
As I mentioned at the car show, I have always wondered why the fliud flows so slowly, when we bleed my brakes. To me this kind of explains it, as it is just a smaller hole, and when you think of how many feet of line there is, plus that it is going through a 4 piston caliper, and then out those silly small bleeders...it ain't no fire hose.
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heirfaus
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Re: Brake Indicator Switch and Brake System Balance

Postby heirfaus » 02 May 2010 15:31

Byron510 wrote:There is no proportioning valve in a PL150 – we know this, and the "restrictor" isn't much of a restriction when you think about how little fluid is actually traveling through the line.


Excalty what I was thinking/saying the whole time. Thanks for taking the measurements to confirm the sutiation!! :D
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Re: Brake Indicator Switch and Brake System Balance

Postby thisismatt » 02 May 2010 21:12

So if the restricter doesn't add to any biasing by means of restricting flow, then how does a standalone brake proportioning valve work if flow restriction has no bearing?
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Re: Brake Indicator Switch and Brake System Balance

Postby Byron510 » 02 May 2010 21:31

thisismatt wrote:So if the restricter doesn't add to any biasing by means of restricting flow, then how does a standalone brake proportioning valve work if flow restriction has no bearing?


A proportioning valve works on limiting the pressure "proportionally" from input to output - it doesn't restrict flow at all. The limiting pressure value is set at X (your adjustable point), and the slope that the pressure increases from this point is preset by the valve itself (I believe that the slope is not adjustable). As an example, I explained it to one member here as the same principal that the Oxygen regulator works on your gas welding rig; input might be 1500 psi from the bottle, but the max output is whatever you want it to be (1, 2, 5, 10 or 40 psi, what ever you like). I don't know if this helps, but it's ultimately the pressure we are regulating in the system with an adjustable proportioning valve, not the flow: The amount of actual fluid movement in a brake system is marginal.

An example of flow in a brake system; I know we've all bled our brakes numbers of times (at least you better have!). Take one full stroke of the pedal in a 510 M/C, bleed that single strokes work of fluid into a container. One strokes fluid from a 510 brake system can be easily held in the cupped shape of the palm of your hand. The stroke equals 4" of pedal travel. Now on a stock disc/drum system, we have about 1/2" of actual pedal movement (on a properly bled and functioning system). That amount of fluid is negligible, and a restriction like I talked about above to such a small amount of fluid would equalize nearly instantly. The reaction time on pressure equalization on a rear disk converted 510 would be even better, as there is even less fluid flow since the cylinders don’t back off like a drum brake system will (assuming your rotor run out is good, like it should be. The system goes strait to transferring pressure, unless you’ve limited the amount of pressure mechanically by use of a brake balance bar (twin master system) or used a proportioning valve or “regulator”.

Hope this helps,
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icehouse
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Re: Brake Indicator Switch and Brake System Balance

Postby icehouse » 03 May 2010 10:16

Byron that is awesome you found some parts to measure for the cause! I should really get the parts to do a bench test and see what the pressures really are when the system is working. My only reason to believe my original idea is my S13 has a 1 to 1 valve built into the master with no brake light indicator switch hooked to it (they are in the caps), there for it has to do "something" and it also has the same type of brass union near the firewall. Seems odd to still use both of the same devices on a 4 wheel disk brake car if they don't do anything why spend the money putting them in....
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Re: Brake Indicator Switch and Brake System Balance

Postby datzenmike » 03 May 2010 12:18

Wolfman do you mean the reservoir caps?? That's the low fluid level warning. It lights the BRAKE light just like the E brake on or loss of fluid in one of the systems. If you mean something else just disregard this.
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Re: Brake Indicator Switch and Brake System Balance

Postby icehouse » 03 May 2010 13:47

datzenmike wrote:Wolfman do you mean the reservoir caps?? That's the low fluid level warning. It lights the BRAKE light just like the E brake on or loss of fluid in one of the systems. If you mean something else just disregard this.


Yeah basically the same idea as the 510 switch, just to warn the driver there is something up with the brake system. It seems smarter in the cap, before the system fails there is a warning. My buddies wagon wore through the rear brake line (the one on the axle, it was low :) ) at first it would just drain the master every couple weeks, when it got worse it would drain quicker. It would have been nice if the light came on when the reservoir was low so bleeding wasn't required on every fill up until we fixed it :)
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Re: Brake Indicator Switch and Brake System Balance

Postby cjr198car » 26 Jul 2011 22:03

Can the brake assembly switch "fail" locking pressure to the front or rear brakes? I used a torch on the brake assembly switch to remove the brakes lines. After reassembly the rear brakes build pressure over a few miles eventually locking up. Im trying to determine if its a bad 280Z MC installation or the brake assembly switch. Im leaning towards to brake assembly switch, but I dont know. Thoughts?

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Re: Brake Indicator Switch and Brake System Balance

Postby cjr198car » 26 Jul 2011 22:14

More info...

I was told that Im releasing pressure from the front brakes (bleeder on MC closest to the firewall), but this is releasing pressure from my rear brakes...

?

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Re: Brake Indicator Switch and Brake System Balance

Postby Byron510 » 27 Jul 2011 22:24

cjr198car wrote:Can the brake assembly switch "fail" locking pressure to the front or rear brakes? I used a torch on the brake assembly switch to remove the brakes lines. After reassembly the rear brakes build pressure over a few miles eventually locking up. Im trying to determine if its a bad 280Z MC installation or the brake assembly switch. Im leaning towards to brake assembly switch, but I dont know. Thoughts?



Well, yes there is a possibility that something could go wrong if the O ring in the sliding piston got fried when you heated it up - it's very possible considering how well aluminum transfers heat. However a failed switch (if not leaking externally) would essentially make your dual circuit brake system a single circuit brake system :shock: , but it would still work.

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Re: Brake Indicator Switch and Brake System Balance

Postby RMS » 03 Nov 2015 16:03

getting close to installing my brake lines and Byron mentions proportioning (because of the 280 brakes and stock drums).
being a busy guy he did not have the time to walk me through it so I thought i would stoke this thread.

I followed berts link to tilton and the product has changed. .... looks cool and it looks like I can keep the lines under the car and just have the nob in side.
Image

with 280 brakes and stock drums(for now) is this the way to go ?
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Re: Brake Indicator Switch and Brake System Balance

Postby Byron510 » 03 Nov 2015 16:17

I have found that with 280ZX front brakes and stock rear drums running regular brake pad material and a 7/8 or 15/16" MC, I have too much front brake in the system - the rears are doing nothing at all.

This is why I have been a advocate of the twin cylinder/ balance bar brake set up since I’ve tried it. A balance bar does correct the situation with a linear curve which doesn't happen with a brake proportioning valve.

What are everyone else’s' experiences?

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Re: Brake Indicator Switch and Brake System Balance

Postby bertvorgon » 03 Nov 2015 18:11

My experience:

While not lineal..requires a few turns to get to a "point" of what YOU may determine is a good sweet spot.

As pads heat up, things change BIG time from when you maybe set it cold, or, weight changes in the car..IE fuel load, crud in the trunk, etc..

It still worked just fine. I would go out and get everything up to smoking hot..IF that is what I thought I was going to be doing...got some rear lock up...and then backed it off a bit from there..no problem.

Rear lock up is NOT an option in my opinion, because if you get that on a turn in, under braking, you could loop the car.

So, for my "normal" street driving, which as most of you know, does involve some good braking on our drives. I have a good "portion" to the rear, enough to both help with keeping front weight transfer to a minimum, and make the rear do some serious work, with out EVER locking the rears. That suites my driving style and how my car is set up. I have a mark on my knob for my "normal" setting, and then I know how many turns to get to my so called race setting. I have not touched that knob since our track days.
"Racing makes heroin addiction look like a vague wish for something salty" - Peter Egan

1973 2Door Slalom/hill climb/road race / canyon carver /Giant Killer 510
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