Proportioning valve - yes or no?

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ReijerLincoln
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Proportioning valve - yes or no?

Post by ReijerLincoln »

With safety in mind, I'd like to convert my '64 from a single to a dual chamber brake master cylinder. This splits the front and rear brake circuits, so a failure or leak at one end won't result in a total loss of brakes. The smaller chamber services the rear wheels, the larger chamber services the front wheels and accommodates the need for greater braking power for the front wheels.

Is a separate proportioning valve needed when converting a 1961-1964 Continental with front and rear brake drums, from a single to a dual chamber brake master cylinder? In other threads knowledgeable forum members toddallen, autostick and jleonard have reported no problems after upgrading to a dual master cylinder without a proportioning valve. With safety in mind, the reason I'm still asking this question is printed in bold in the quote below:
Proportioning Valve
The proportioning valve is designed to prevent rear wheel lockup during panic braking. It is needed for two main reasons - most vehicles use drum brakes in the rear and all vehicles experience weight transfer during a panic stop. Rear drum brakes are hydraulic over mechanical in design. If too much pressure is supplied to the wheel cylinders, lockup will occur. All vehicles, those with both rear drum and rear disc brakes, will experience weight transfer during a panic stop. When weight is taken off the rear wheels during a panic stop the tendency for the rear brakes to lockup will increase. The proportioning valve is designed to limit the pressure to the rear brakes during a panic braking situation.

The most important point to understand about proportioning valves is when they work - only during panic braking. This means that a vehicle could potentially go its whole life without ever using its proportioning valve
. Think about the little old lady that drives to and from church and the grocery store. It is possible that she will never have the need to make a panic stop and therefore never activate her proportioning valve. The other half of that equation is all those who drive near her will probably get a chance to see if their proportioning valves work!
Source: http://www.studebaker-info.org/tech/brakes/bf50014.html Thanks to Gary/kultulz for the link.

Cheers,
Reijer



Addendum:
This topic has come up before in several threads, I know. But the discussion seems to veer off the road when front (and rear) disc brake conversions are thrown into the mix, as well as when confusion arises over the differences between proportioning valves, metering valves and pressure difference switches.
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Re: Proportioning valve - yes or no?

Post by mechatech »

If it were my car I would put one in. That one time your car swaps ends and hits a wall is the time you'll wish you did it.
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Re: Proportioning valve - yes or no?

Post by AnthLinc »

I'd called Lincoln Land. They have developed and sold different combinations that are cost effective compared to the old parts. I have disk brakes and converted my 1966 with the dual master cylinder and last year up graded to a modern combination valve from them. It saved me $300.00. They many have a more affortable suppliments that could work for your 4 wheel drum brakes. It may be the best place to go for that advice.
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Re: Proportioning valve - yes or no?

Post by 66Lincoupe »

ReijerLincoln wrote:...The smaller chamber services the rear wheels, the larger chamber services the front wheels and accommodates the need for greater braking power for the front wheels...
The larger chamber compensates for the larger volume of fluid that disc brakes use. The piston size (diameter) of the master cylinder dictates how much hydraulic force is transferred to the fluid and the wheel cylinders.

Here is a good tech article: http://www.auto-repair-help.com/automot ... linder.php

Some older GM drum/drum cars used a dual chamber master cylinder with equal sized reservoirs...

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A proportioning valve is a good safety upgrade. A combination valve (Proportioning/metering/distribution valve) on 4 wheel drum is an unnecessary addition I think since the metering portion of the valve holds off sending pressure to the disc brakes in the front (since disc brake pads are always in contact with the rotor) until a threshold pressure is reached in the rear drum brakes which are pulled away from the drum by springs after the brake pedal is released. In a disc/disc car or a disc/drum car a combination valve will reduce dive (when the front bumper dives toward the ground under braking) when stopping...
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Re: Proportioning valve - yes or no?

Post by jleonard »

Reijer,

You don't need a proportioning valve if you stay with the stock four wheel drum brakes, even if/when you convert to a dual master cylinder. The factory engineers designed the wheel cylinder bore diameters to provide the appropriate front/rear brake balance.

Disc/drum systems need a prop. valve because disc brakes need much higher fluid pressure to provide the necessary braking force. The prop valve is really just a fluid pressure regulator that reduces the fluid pressure to the rear brakes.

Four wheel disc systems may need a prop valve, although proper selection of rotor diameter and caliper piston diameter can mitigate this.

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Re: Proportioning valve - yes or no?

Post by jleonard »

BTW, I disagree with the quote you cited from the Studebaker web site. Proportioning valves have an effect under all conditions, not just panic stops. Otherwise they wouldn't be called PROPORTIONING valves. They would be called limiting valves or something like that.

And weight transfer isn't the ONLY reason a prop valve is needed. While weight transfer is real during panic braking, disc/drum systems need prop valves because the braking systems are quite different.

Drum (well, since the 1930s or so) brakes are self-energizing. They are designed such that the friction forces applied by the drum to the brake shoe tend to increase the braking force applied. If there weren't return springs on the shoes, releasing the fluid pressure wouldn't release the brake. At least not until the drum rotates in reverse. If you've ever replaced brake shoes, you'll remember just how strong those return springs can be.

Disc brakes are not self-energizing. The fluid pressure simply clamps the pads against the rotor. If you remove the fluid pressure, the stopping force reduces to almost nothing.

The end result is that disc brakes require more fluid pressure to apply the same braking force. So if you apply 500 psi to a front disc brake system and the same 500 psi to a rear disc brake system, you may find the rear wheels skidding while the fronts are not. For obvious reasons this isn't desireable. The proportioning valve is designed to reduce the rear pressure to provide balanced braking forces.

- John
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Re: Proportioning valve - yes or no?

Post by TonyC »

I agree, do it--get a combination proportion valve when you do the upgrade. Even when I didn't fully understand the details of its purpose, I still retrofitted a '67 valve into Frankenstein's brake system when I rebuilt it. It shouldn't be that difficult to do for your car.

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Re: Proportioning valve - yes or no?

Post by mechatech »

Scans from Auto Mechanics Fundamentals by Stockel, an entry level trade school text book.
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Re: Proportioning valve - yes or no?

Post by ReijerLincoln »

AnthLinc wrote:I'd called Lincoln Land. They have developed and sold different combinations that are cost effective compared to the old parts. I have disk brakes and converted my 1966 with the dual master cylinder and last year up graded to a modern combination valve from them. It saved me $300.00. They many have a more affortable suppliments that could work for your 4 wheel drum brakes. It may be the best place to go for that advice.

I contacted LincolnLand... and the plot thickened. Da-da-da-dum! They used to sell a conversion kit for '64 but stopped selling it after many complaints about a hard brake pedal with little or no boost, leading them to conclude that a dual master cylinder is not compatible with the original 1964 booster.

As far as I can tell, toddallen and autostick are the only forum members who use a dual master cylinder on a front drum/rear drum car and are happy with the result. Their car however is a '63 and has a different booster. Still, can the '63 and '64 booster be that different? I'm wondering if the people who were unhappy with their '64 kit from LincolnLand had not shortened the booster push rod to approximately 3-11/32"?

I contacted Baker's Auto about their kit. It's a bolt-on deal and warrants no proportioning valve. There was no mention of a hard brake pedal with little or no boost. I'm going to ask about them about this.
Edit: Baker's Auto also notes a harder/firmer brake pedal but has seen nor heard of any other side effects to the upgrade.


I also spoke to John (Jleonard) from Gearheadengineer, who mentioned that his kit will work on a front drum/rear drum car but it will make the brake pedal feel somewhat firmer than original. (He explained that his kit is designed to work with four wheel disc or disc/drum combinations. It will work with four wheel drums too, but because his dual master cylinder uses a larger piston diameter than the stock single master cylinder the brake pedal will feel somewhat firmer than your original). John, any thoughts on the lack of boost that LincolnLand reported? Perhaps they used a different dual master cylinder than you do?

Cheers,
Reijer
Last edited by ReijerLincoln on Fri Apr 06, 2012 2:49 am, edited 2 times in total.
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Re: Proportioning valve - yes or no?

Post by Solid »

ReijerLincoln wrote:
AnthLinc wrote:I'd called Lincoln Land. They have developed and sold different combinations that are cost effective compared to the old parts. I have disk brakes and converted my 1966 with the dual master cylinder and last year up graded to a modern combination valve from them. It saved me $300.00. They many have a more affortable suppliments that could work for your 4 wheel drum brakes. It may be the best place to go for that advice.

I contacted LincolnLand... and the plot thickened. Da-da-da-dum! They used to sell a conversion kit for '64 but stopped selling it after many complaints about a hard brake pedal with little or no boost, leading them to conclude that a dual master cylinder is not compatible with the original 1964 booster.
Won't you get the hard pedal if the master cylinder is not sealed properly against the face of the booster? I have not done the disc conversion yet (waiting to do bushings, springs, and four wheel disc in one shot) but on my '62 the rebuilt booster and dual reservoir master does not result in a hard pedal, if anything I'd say it's softer than I'd like and sort of numb. In fairness that is the classic American luxury car approach (why would you want to feel the road?), but I'm used to driving modern sports cars so pretty much everything about driving the Lincoln feels weird and its handling has a sort of Newtonian physics character to it that endlessly amuses me. If switching really results in a harder pedal though, I'd welcome it, since I think there would be more feel that way.
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Re: Proportioning valve - yes or no?

Post by autostick »

ReijerLincoln wrote:As far as I can tell, toddallen and autostick are the only forum members who use a dual master cylinder on a front drum/rear drum car and are happy with the result. Their car however is a '63 and has a different booster. Still, can the '63 and '64 booster be that different? I'm wondering if the people who were unhappy with their '64 kit from LincolnLand had not shortened the booster push rod to approximately 3-11/32"?
I contacted Baker's Auto about their kit. It's a bolt-on deal and warrants no proportioning valve. There was no mention of a hard brake pedal with little or no boost. I'm going to ask about them about this. Edit: Baker's Auto also notes a harder/firmer brake pedal but has seen nor heard of any other side effects to the upgrade. Cheers, Reijer
Thanks Reijer for the acknowledgement, but I doubt if Todd and me (Ken) are the only ones who have done this. Anyway I have made some pretty quick stops without having the rear lock up, both with bias ply tires and with radial tires. As for the "harder" brake pedal this is a pretty subjective concept. So I will try to describe in words how it felt differently after the single to dual master conversion, that included shortening the pushrod.

The brake pedal had less travel and required less foot pressure to stop the car. The difference was noticeable, like the contrast between regular and power brakes back in the day when it was an option. Stepping on the pedal gave a more immediate response, similar to what happens after bleeding the brakes to remove a few air bubbles from the lines. I thought I could lock up the wheels if I really pressed hard on the brake, something I did not feel I could with a single master. I say this was a feeling, as I have never been in a four wheel lock up in this car. The dual master made the car easier to stop. Now this is sort of opposite of what Solid observes, so there is obviously some variation between cars or some variable that nobody has mentioned yet. In my case I did not do anything with the booster, it was the same before and after.
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Re: Proportioning valve - yes or no?

Post by ReijerLincoln »

Thanks for noting your experiences solid and Ken. I'm going to order a kit and see how it performs. I wouldn't mind the pedal travel that Ken notes but the boost of course has to be right. If I can't sort it out, I'll revert back to the original set-up.
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Re: Proportioning valve - yes or no?

Post by jleonard »

John, any thoughts on the lack of boost that LincolnLand reported? Perhaps they used a different dual master cylinder than you do?
Probably a combination of a tired booster and the larger piston on the dual master cylinder. Unlike many other cars, the Lincoln boosters don't always fail completely in one event. The amount of assistance (boost) provided by the booster can gradually reduce over time. So you may have a weak booster without realizing it. And disc brake master cylinders use larger piston diameters than drum masters, because disc brakes require more fluid volume due to the large caliper piston diameter. Since force on a piston = pressure * area, the larger bore master requires more pedal pressure to provide the same amount of brake pressure. Add this to a weak booster and you may find the pedal pressure to be unacceptable. Another possible factor is a vacuum leak - these cars have a lot of vacuum systems and a leak in any one of them will reduce the brake booster's effectiveness.

Keep in mind that acceptable pedal pressure is subjective. As Solid notes, the '60's American luxury cars are known for a very soft brake pedal. Almost no pedal feel at all, but you can stop the car with one toe on the pedal. Some drivers like this, and some don't.

Ken's experience makes perfect sense. The larger piston diameter on his dual master means less pedal travel is required to move the same amount of fluid. So the brakes give a more immediate response.

'65 and up Lincolns use a different booster than the earlier cars. It provides more boost, probably because the factory switched to disc brakes that year.

I run a rebuilt '64 booster on my car, with four wheel disc brakes and a largish bore dual master cylinder. The pedal is firm, but I'm comfortable with it. For a drum brake car, I think Reijer will be perfectly happy with the pedal feel from a dual master cylinder conversion.

I am working on a replacement booster/master set up to provide the old school soft braking feel. I'll probably have the prototype installed on my car by early May so I can test it out.

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Re: Proportioning valve - yes or no?

Post by dcm5652 »

A smaller bore master cylinder will give you an easier brake pedal while a larger bore master cylinder will give you a harder pedal, if you want a softer pedal go to a smaller bore master cylinder and if you want a harder pedal go to a larger bore master cylinder, the smaller bore will have more travel and the larger bore will have less travel.
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Re: Proportioning valve - yes or no?

Post by Solid »

autostick wrote:The dual master made the car easier to stop. Now this is sort of opposite of what Solid observes, so there is obviously some variation between cars or some variable that nobody has mentioned yet. In my case I did not do anything with the booster, it was the same before and after.
To clarify, I have only driven the car with a freshly rebuilt booster (well, not counting moving it around with the booster not working). I only know the pedal feel with a rebuilt booster and the dual reservoir master (as both original parts were non-functional when I got the car), new flex lines, and new wheel cylinders on all four corners. I filled with ATE Super Blue and bled it thoroughly, so this is as firm as it's going to get. I don't find it hard to stop the car - it stops just fine (if a bit wobbly with all my warped drums) - I just find the pedal feel to be excessively vague while accepting that as fairly normal for an old American luxury car. If the single reservoir master is even softer... well... no thanks!
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