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PostPosted: September 21, 2016, 12:25 pm 
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Location: BC, Canada. eh?
BTW - Wilwood also make a hydraulic front/rear inline hydraulic proportioning valve (I have one, and will be installing it when I build my brake lines). It allows you to change your rear braking from where it is now to virtually 100% forward, or anywhere in between, by turning a knob.

I believe that would solve your problem, and cost less than changing the master cylinder (Summit has 'em for around $42USD....)

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PostPosted: September 21, 2016, 9:49 pm 
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Those are very small master cylinders. I am surprised you are not using up all the piston travel in the masters and easily locking up the brakes due to a very light pedal effort. What is the pedal ratio?

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PostPosted: September 21, 2016, 11:29 pm 
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This is what the pedal box looks like


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PostPosted: September 22, 2016, 6:59 am 
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zetec7 wrote:
BTW - Wilwood also make a hydraulic front/rear inline hydraulic proportioning valve (I have one, and will be installing it when I build my brake lines). It allows you to change your rear braking from where it is now to virtually 100% forward, or anywhere in between, by turning a knob.

I believe that would solve your problem, and cost less than changing the master cylinder (Summit has 'em for around $42USD....)

Speaking of Wilwood proportioning valves, does anyone know how they operate? Are they linear with a pressure cap, linear with a knee and reduced pressure, or produce an across the board pressure reduction?

Bill


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PostPosted: September 22, 2016, 11:05 am 
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I might have come up with the perfect no cost solution. After playing with the spreadsheet for hours, looking at what master cylinders are available. The light bulb came on, Swap the calipers front to rear. They are both the same brand and model Wilwood Dynalight Forged, but the rear has larger pistons area, (3.0 to 4.12) Once swapped I will be within a couple of percentage points of the idea with the same lever pressure give or take a couple of pounds (72 to 69).

I have a new brake proportioning valve for my TR8 arriving today, so it looks like I will be spending all Saturday playing with brake fluid:)

Graham


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PostPosted: September 22, 2016, 11:54 am 
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That sounds good. It's certainly good to try something with the parts in hand to get perspective, but this sounds just right. I don't know numbers on this, but the pedal pressure sounds good to me too.

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PostPosted: September 22, 2016, 12:23 pm 
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FastG wrote:
I might have come up with the perfect no cost solution. After playing with the spreadsheet for hours, looking at what master cylinders are available. The light bulb came on, Swap the calipers front to rear. They are both the same brand and model Wilwood Dynalight Forged, but the rear has larger pistons area, (3.0 to 4.12) Once swapped I will be within a couple of percentage points of the idea with the same lever pressure give or take a couple of pounds (72 to 69).

I have a new brake proportioning valve for my TR8 arriving today, so it looks like I will be spending all Saturday playing with brake fluid:)
Graham, glad the spread sheet has been helpful to you. Looks like you are on the path to a good solution. As close as you are in theory, you should be able to dial it in for the real world with the balance bar. Adding a proportioning valve as a safety valve for high line pressures can help make sure the rears never lock first.

BBlue wrote:
Speaking of Wilwood proportioning valves, does anyone know how they operate? Are they linear with a pressure cap, linear with a knee and reduced pressure, or produce an across the board pressure reduction?
Bill, if I correctly understand how they work, they have no effect until the preset line pressure is reached, then provide a linear reduction in pressure thereafter. Different brand valves seem to spec different reduction percentages.

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PostPosted: September 23, 2016, 7:57 am 
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Tom, that seems to be the popular perception and, but I have never seen anything that confirms that notion. Or even suggests it. Wilwood offers no explanation, which I find to be rather peculiar. A company that is an industry leader and offers no data on their products performance.

Bill


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PostPosted: September 23, 2016, 8:12 am 
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My machinist friend is convinced that Wilwood makes "show" brakes.

He uses a lot of bad words when I take him Wilwood parts to work on.

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PostPosted: September 23, 2016, 9:22 am 
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In your picture of the pedal set you can see the shape of the clevis's is symmetrical. That description I wrote above assumed the side of the clevis facing the balance tube would be flat without rounded shoulders. That helps capture the balance tube if one circuit fails. I'll try to get you a picture just so you know, but there's not much you can do about it unless you want to make new pieces.

Sigh...

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PostPosted: September 23, 2016, 1:55 pm 
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BBlue wrote:
Tom, that seems to be the popular perception and, but I have never seen anything that confirms that notion. Or even suggests it. Wilwood offers no explanation, which I find to be rather peculiar. A company that is an industry leader and offers no data on their products performance.
Bill, Fred Puhn's book (Brake Handbook) has a lengthy explanation of how proportioning valves work. Also, Tilton and AP Racing web sites might offer more information. My comments kind of netted out my reading of Puhn's explanation.

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PostPosted: September 24, 2016, 6:31 am 
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BBlue wrote:
Speaking of Wilwood proportioning valves, does anyone know how they operate?
It's FM*, man... Totally FM*...








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PostPosted: September 24, 2016, 7:24 am 
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Tom, I read sections of the book years ago. As I recall, he described three types of valves, constant percent reduction, pressure limiting and the type you describe. Wilwood describes their valve as giving up to 60% reduction of pressure. That's all. To me, that sounds like a constant reduction valve, the least desirable type. I suppose we will never know, unless some curious soul sets up a test rig, measuring input and out pit pressures across a wide range of pressure.

Gonzo, yes indeed, it is FM. But hey, that describes all hydraulic circuits.

Bill


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PostPosted: September 24, 2016, 7:29 am 
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Hey Bill-
Oddly enough, I was just reading in the "Introduce Yourself" thread, and there's a semi-new guy called "ntsqd" in there that says he used to work for Wilwood. Perhaps iffen you were to ask him real nice, he'd tell us what kind of incantation and/or animal sacrifice they use for the pressure reduction... :mrgreen:

:cheers:
JD

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PostPosted: September 24, 2016, 1:14 pm 
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Bent Wrench wrote:
My machinist friend is convinced that Wilwood makes "show" brakes. He uses a lot of bad words when I take him Wilwood parts to work on.


Been pondering this one since you posted it. Which / what does he recommend then?

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