Brake Indicator Switch and Brake System Balance

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Brake Indicator Switch and Brake System Balance

Postby Byron510 » 08 Mar 2010 22:22

Con't from this previous discussion which was totally thread jacking a guys new purchace, but is a relevent discusion concerning the operation of a brake system, specifically in a 510.

from....

viewtopic.php?f=1&t=14175&start=30
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Re: Brake Indicator Switch (presure failure switch)

Postby Byron510 » 08 Mar 2010 22:25

bertvorgon wrote:Seeing as I have unleashed some sort of monster on this thread, I did some checking on things today.
#1) I am going to take both the shuttle valve apart, and the brass "T" at the firewall.

The reason for this, is so that we all may put this to rest, as to what the 510 brake system is really doing. I say this because I learned something today, after making some phone calls. One was to the BRAKEMAN caliper manufacturer, which is what I run on my car's front. They are very friendy, and willing to discuss things, when you kinda sound like you know what is going on. Their web site is filled with some very good technical stuff also. The other call was to Andy at Specialty Engineering. For those of you who are not local, or know of Specialty, he has built some of the fastest 510's in North America, let alone the other race and street cars he has built. He has installed more braking systems, from mild to wild, than the sum total of most of us on this site.

#2) I am not a brake expert, I only know what has worked for me, and generally how they work, so I will attach here, both the links to the BRAKEMAN's technical section.

http://www.thebrakeman.com/valvetechi
http://www.thebrakeman.com/valvetechii

This will help explain a few things, one major one being the "RESIDUAL VALVE". This may be what the issue is with the brass "T" on the firewall, and/or, what the shuttle valve is doing....maybe.

As I talked to the BRAKEMAN person, he brought up the spectre of the residual valve, and how it figures into drum brake sysytems, and/or the problems it can cause if left in. Read the above and you may understand. Now, years ago, I vaguely remember the residual valve issue crop up, but just ignored it as I thought it really did not pertain to our cars. I may prove to be wrong, which will be fine, as we all need to understand how our systems work.

When I talked to Andy, he has never removed the brass T on street modified cars, and in some race car cases! Others of course, got the full re-plum, and any residual valve issues...well, they just were not there. I know I have never had any issues with dragging pads on the back, at least that I would have ever noticed. That being said, we need to really look at how the 2 offending parts are constructed.

#3) Could someone, with a true factory manual, see if it discusses anywhere in the brake system, the shuttle valve, and the brass T at the firewall.

#4) if the T is the residual pressure valve, it will have a small spring in it, behind that small orifice. Jason has one at his place, and I am going to take it apart, even if I have to saw it open to really see what is inside.

to be continued......
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Re: Brake Indicator Switch (presure failure switch)

Postby Byron510 » 08 Mar 2010 22:52

OK Bert,

I dug through my achieve for research, and my scanner sucks. So I took photos of the relevant pages with info you were looking for.
I first looked in the Service Manual, Datsun, Model 510 Series - Chassis and body, and found no reference what so ever to the fact that a510 even has a tandem brake system. It did cover both disc and drum front brakes - strike one!
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Next I figured I go through my collection of Datsun Service Bulletins, I have one introducing the 510 series in Aug 1967, it has a nice photo of a single circuit system; with an inlay of a front disc brake... strike two.
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OK, so I figure, well the 1969 model update should have it; even though most US bound 68's got tandem circuit brakes (I know not all of them, but most did); all Canadian 510's got the single circuit brakes for the 1968 model year, but both Canada and the US got tandem brakes in 1969, so there must be an update for the 1969 model year, right? Well yes, there is mention of the tandem brake cylinder and a nice exploded view on one, but no info other than this... strike three.
Image
I figure I'm done, but wait - what about the Datsun Parts Catalog...
I got this page, and thought I’d run out of options Bert...
Image

Then I flip over the page and I have this - pay dirt!
I found the diagram you asked for Bert; Item 8.01, P/N 46100-26100 and it's officially called a "Assy Brake Indicator Switch"
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Image

You guys are bringing up some interesting info. Out of all the years I have been playing with 510's, I had no idea that there was a restriction built into the “T” at the front of the transmission tunnel - thanks Jeff.

As far as the hydraulic action and how different M/C piston size, front caliper piston size and rear drum piston size all add up, I have to think about how to explain it in fluid dynamics and pressure. However, as I understand it:

A 1” M/C cylinder bore with 100 lbs of pedal pressure traveling 1” distance in the bore will exert 100 lbs of line pressure (assuming a pedal ratio of 1:1 – which it isn’t, I know, but were are only talking theory here). This 100 lbs line pressure acting on a 4” front caliper bore will net 400 lbs of force but only travel .250” of distance, and inversely the same M/C will exert 50 lbs pressure on a ½” bore but travel twice the distance of the M/C (2” travel at the rear ½” cylinder. Someone correct me if I’m wrong here.
So increasing the front caliper piston size (or the square area of all your pistons added together for multiple piston calipers) will decrease the amount of piston travel, however increase the pressure available.
At the same time an equal amount of fluid is acting on the smaller rear wheel cylinder engaging the rear brakes faster than the system was intended for the given braking scenario (because in dislexidimes car it has a tandem M/C, and equal amount of fluid at equal pressures is being delivered to both circuits – brake switch indicator issue aside). Remember that a drum brake is self engaging and requires very little pressure to actuate its design.
You are not slowing down because the front brakes (where 75% of the braking work takes place) have not yet engaged, so you will push harder to try to slow the car down. Now you have a situation where the rear line pressure is way higher than a stock brake system would have normally had for this same given situation (because the front calipers have not engaged due to lack of piston travel), more pressure builds at the rear = more force on the rear cylinders = IMPENDING DOOM!
“What we have here is a failure to communicate” … or a failure in design because the engineered design of the 510 brake system as a whole has been screwed with, and it’s two individual circuits are no longer balanced.
I hope I got this right – it took a five tries….(and likely confused the hell out of few guys that were reading between edits)
The fix here is obviously balancing the front and rear M/C sizes if a tandem system is used. And since this is near impossible given the few choices we have.
The next best thing is a balance bar between two single M/C’s to balance the tandem circuit. This means lots of fabrication, but hey this is how rear race cars are built and it’s the best option. This balance bar gives a linear adjustment of both circuits, allow you to mechanically adjust the amount of pedal pressure each circuit is given.
The next option to fix the problem is an adjustable proportioning valve, which limits the pressure to a single circuit that it is plumed into. This is the easier route most people take. An adjustable proportioning valve is not linear, but it does seem to work for most applications.

I’ve driven badly biases brake systems – it’s scary. Anyone out there running 280ZX front brakes and stock 510 rears, you have a badly front biased system that will not allow the rears to do anything at all.

Also this discussion has nothing to do with pad materials. Want to really screw up your bias – put a set of metal masters in the front and go driving! Cold brakes, rainy night – you’re toast!
Anyways, too many of my thoughts on the subject.
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Re: Brake Indicator Switch (presure failure switch)

Postby Byron510 » 08 Mar 2010 23:35

So, now lets talk brake switch indicator here: (not the brake light switch, the brake pressure switch):

If the above scenario that I wrote was out of whack far enough, Jeff I could see that the brake switch indicator could light. However, to get the system that far out of whack would be really extreme, IMO.
We’re talking very small amounts of circuit difference here can make huge differences in the brake system balance, and the piston inside the switch appears that it can travel quite a long ways before it will activate.
Because both circuits of a tandem system work on opposing sides of this switch, and because the system pressures differ so little from front to rear even on our miss matched, played with brake systems, the switch still cannot be triggered. You literally have to have either a void in one circuit (air) or an outright failure (leak) in one circuit to activate the brake switch.

Now add in this restriction affect in the rear brake line “T”, add in two totally different brake types (front disc, rear drum), add in the brake pedal ratio, add in accounted wear on the rear shoes and a possible mal-adjustment, add in the difference between the pad materials on the front discs and the rear shoes, add in different types of weight transfer (panic vs. controlled), add in a weight bias difference in the car itself….. Man if you come up with a formula to make this work in our 510’s, I’ll but you beer for a year! :shock:

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Re: Brake Indicator Switch (presure failure switch)

Postby Byron510 » 08 Mar 2010 23:40

thisismatt wrote:A dual bmc has springs inside of it which affect when and how much pressure is applied to the two systems during the brake pedal stroke.


Geez Matt, you're totally right, and I missed this variable - at that to the above beer list! 8)
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Re: Brake Indicator Switch and Brake System Balance

Postby thisismatt » 08 Mar 2010 23:55

I'm your huckleberry.

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Re: Brake Indicator Switch and Brake System Balance

Postby 510rob » 09 Mar 2010 00:10

Jeff brought up a good point about the notion and significance of what he is calling the 1:1 valve...

Let's first unpack the terms so that we can all understand the concepts together...

Pressure is defined as a resistance to flow.

Force is NOT pressure. The terms are NOT interchangeable. Pressure implies units of force divided by units of area.

If I said 100 lbs, that implies 100 lbs force. If I said 100psi, that implies 100pounds per square inch, which is a pressure --> force over area. On each square inch of area there will be 100 lbs force applied...

If the master cylinder is 1 square inch, and I apply 500 lbs to it, I will generate 500 pounds per square inch, so I have 500 psi line pressure, presuming there is no flow...

In a sealed fluid system, once the receiving-end fluid cylinder (in this case, the wheel cylinder) has moved through its full stroke capacity, and cannot absorb any more transitive fluid capacity, you will develop a system pressure. That pressure will be proportional to the force applied to the input fluid cylinder (in this case the brake master), and that cylinder's moving area.

In a case where both input cylinders are tied together (tandem master cylinder), what if the stroke volume on one end (front brake circuit) is greater than the stroke volume on the other end (rear brake circuit)? If that is the case, and both circuits are completely isolated in a fluid sense, then you can develop a pressure at one end before you develop equal pressure at the other end (isn't this a brake force imbalance?). A way around this would be to equalize pressures at each end by using a floating & isolated shuttle 'equalization block' as Jeff has suggested (the 1:1 proportioning valve that I prefer to call an equalization block as opposed to a 1:1 proportioning valve - essentially semantic equalities). The 1:1 valve must maintain equalized front to rear pressures, by logical necessity. (unless my logic sucks ass, in which case my theory must also suck ass by logical necessity). Refer to Pascal's Law...

Once we introduce that concept, we must also consider another concept. If you start to juggle around slave cylinder sizes, you will modify the relationship of front to rear stroke capacities, as well as front to rear generated forces. Without the use of the equalization block, you might develop unequal forces, which may lead to imbalanced fluid forces front to rear (maybe we should retitle the equlaization block as a Pascal's block? I dunno...)

So many other things come into play. What about friction coefficient of front brakes versus rear brakes? What about the increase or decrease in leverage of say a 280ZX caliper versus a stock 510 caliper, because the 280ZX pads are grabbing their respective rotors at a greater radius than the 510 pads are?

So, now we've got master cylinder spring rates too? fuuuuuuck, this is getting too damn complimicated for me. I think I'll avoid all this BS and install a Tilton pedal box with dual masters and a mechanical force balance bar to set front to rear overall brake balance. Phew, solved properly. :mrgreen:

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Re: Brake Indicator Switch and Brake System Balance

Postby bertvorgon » 09 Mar 2010 06:29

At least we can see, in the shuttle valve, that it is ONLY letting us know if an IMBALANCE is there, due to a circuit failure. Thanks Byron. Less pressure on one side moves the little "shuttle" piston over, which grounds out the circuit and turns the brake warning light on.

Jeez...sorry I mentioned becareful with too much rear bias....... :oops:
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Re: Brake Indicator Switch and Brake System Balance

Postby okayfine » 09 Mar 2010 07:34

Thanks Byron. That all is a better explanation than anything I found in a search yesterday.
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Re: Brake Indicator Switch and Brake System Balance

Postby 510rob » 09 Mar 2010 09:54

bertvorgon wrote:At least we can see, in the shuttle valve, that it is ONLY letting us know if an IMBALANCE is there, due to a circuit failure. Thanks Byron. Less pressure on one side moves the little "shuttle" piston over, which grounds out the circuit and turns the brake warning light on.

Jeez...sorry I mentioned becareful with too much rear bias....... :oops:

Way to go, Keith! Shit disturber. I knew we would have to keep an eye on you after seeing that rat fink on your dash. Ever since you were a teenager, man oh man, always causin' trouble...

I'm still curious to hear Andy's comments on the subject. I don't see the point in the brake balance adjuster thingies that are sold by so many companies. I don't see how they can do what they claim to do, so I avoid them and want them to go away and out of my sight so I don't have to waste my brain thinking about them! Make the mean valve go away!

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Re: Brake Indicator Switch (presure failure switch)

Postby 510rob » 09 Mar 2010 10:09

Byron510 wrote:A 1” M/C cylinder bore with 100 lbs of pedal pressure traveling 1” distance in the bore will exert 100 lbs of line pressure (assuming a pedal ratio of 1:1 – which it isn’t, I know, but were are only talking theory here). This 100 lbs line pressure acting on a 4” front caliper bore will net 400 lbs of force but only travel .250” of distance, and inversely the same M/C will exert 50 lbs pressure on a ½” bore but travel twice the distance of the M/C (2” travel at the rear ½” cylinder. Someone correct me if I’m wrong here.
So increasing the front caliper piston size (or the square area of all your pistons added together for multiple piston calipers) will decrease the amount of piston travel, however increase the pressure available.


place holder for later. I have to go to class, to get classy, or reclassified, or some crap like that.

(Byron, you are right, but your terminology is a bit wrong, so I will clarify a bit of what you have said, you can edit your post, and I will erase this one)

bore diameter vs. piston area.

displacement volume

pressure vs. clamping force.

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Re: Brake Indicator Switch (presure failure switch)

Postby icehouse » 09 Mar 2010 10:28

Byron510 wrote:
If the above scenario that I wrote was out of whack far enough, Jeff I could see that the brake switch indicator could light. However, to get the system that far out of whack would be really extreme, IMO.
We’re talking very small amounts of circuit difference here can make huge differences in the brake system balance, and the piston inside the switch appears that it can travel quite a long ways before it will activate.
Because both circuits of a tandem system work on opposing sides of this switch, and because the system pressures differ so little from front to rear even on our miss matched, played with brake systems, the switch still cannot be triggered. You literally have to have either a void in one circuit (air) or an outright failure (leak) in one circuit to activate the brake switch.
Byron



Yeah it will take a huge differential before the brake light is activated but the system will always have equal pressures front to back. The second picture down proves my theory, the system with a single master has equal pressures front to back, even with the disk brake option. With one master there is no way around that. If the braking system was designed for a equally pressured system with a single master it wouldn't work correctly if the new dual master didn't establish equal pressures, the brake system would be front or rear biased. Now when the "upgraded" to a dual master the only thing they changed was the amount of masters it is still an equal pressure system because the slide in the shuttle valve will always keep the system equally balanced.
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Re: Brake Indicator Switch and Brake System Balance

Postby Rheis » 09 Mar 2010 12:07

I wish somone had put a link on the other page to let people know this discussion had been moved :evil: :oops: anyways took care of it so no one else embarasses themselves. You guys left me hanging there .. I thought 510 guys are supposed to stick together :D. Anyways glad to see everything has been figured out, just came across this also http://www.chevyhiperformance.com/techarticles/71398_install_brake_proportioning_valve/index.html some useful info and it talks about the "proportioning valve" (actualy a combination valve)

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Re: Brake Indicator Switch and Brake System Balance

Postby icehouse » 10 Mar 2010 21:20

Byron I think the drawing you have is slightly off. There is 2 springs, one on each side of the piston. Check out my machining skills :)


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Re: Brake Indicator Switch and Brake System Balance

Postby Byron510 » 10 Mar 2010 22:35

Good work Jeff - I saved that one in my archives :D
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