dual master cylinder

I can verify that a dual system should be well engineered and ideally, each circuit should be tested independently. I say this because of my experiences with a factory system. I have a "beater" '99 Ford F150 that I purchased new. Being in the Twin Cities area in the beginning of its life, it has encountered the usual rust problems, including brake lines. The first to go was one of the rear lines. While it was apparent that there was a problem, the truck was drivable and I was able to get to my shop with no problem and replace the rear lines. A quick bleed, and I was back on the road again.

A few years later, a front line rusted through and it was a completely different story. The brake system was so compromised that there was very minimum stopping power. Luckily, I was less than a couple of miles from my shop (which is on a county road out in the country) and was able to creep back to it. I replaced the front lines, and after a bleed, the brakes were back to normal. I was surprised by this because I did not expect the almost total failure unless something else went wrong.

Maybe it was a design problem on this particular model of truck, but ever since, I have lost the confidence I once had in dual systems.
 
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V8 Bob said:
Gonna have to disagree with some of the above math.

1" master cylinder piston travels 1.27" for 1 c.i. of fluid movement.

1 1/16" master cylinder piston travels 1.12" for 1 c.i. fluid movement.

The 1" piston travel increase is .150", or just over 1/8", not 3/8". This results in pedal travel increase of .750" with a 5:1 ratio, or .9" with a 6:1. As I stated previously, using a 1" is doable in most cases with minimum effort. The resulting higher pressure output with a 1" works better with common disc/drum systems by slightly lowering the pedal effort.
I know converting to a dual master cylinder is the best hydraulic brake upgrade you can make, but does require some thought and extra effort.
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V8 Bob ..... First thing I'm gonna do here is apologize profusely to Bob for ASSUMING that "Pickup's" math was correct. I started to check it last night, but got lazy ..... SHAME!!

Anyway, V8 Bob's math is irrefutable after checking and tells the story in real life terms. I believe the big point here is bringing to light just how important it is to know what you're doing when fooling around with changing M/C bore diameters (or wheel cylinder bore diameters). It's also necessary for folks to realize that DUAL M/Cs require a GREATER stroke distance than normal to operate sufficiently once one of the circuits becomes compromised. And there are so many other details that need to be figured into these upgrades, like pedal ratios, or even the thickness of carpeting or padding below your brake pedal. And most importantly, take the time to create a TEST LEAK in each circuit of your newly-plumbed dual M/C to make sure that your new configuration will actually stop if a leak occurs in one side of your system.

Coop



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alchemy said:
Nothing normal about that in an early Ford. He can get where he needs to be with simple parts and maybe some small adapters. No need for big fabrication.
Click to expand...

My bad, I should have been more specific. When I said a, "Normal" place, I meant, as in today's cars.
 
well this has been educational as usual, I will backup and review the leak issue with dual systems to get a better understanding of the situation. With that said however, growing up on a farm with old grain trucks, it was not that unusual to have to pump your breaks up at times because the brake shoes probably needed adjusted, with those old trucks. would you be able to do that with a leak situation on a dual system? The second observation is this: A leak on a single cylinder system would appear to be just as chaotic because if it leaks off, you have zero brakes, or at least brakes that will disappear each time you pump it until the fluid reserve is empty, at which time the need of the emergency brake as stated by someone is a helpful item. Am I missing something here? I changed to a dual M/C because I wasn't happy with front drum brakes and changed over to the consistency of disc brakes. I think I would probably have liked to have a better understanding of the calculations involved before choosing a M/C . I may look for a M/C with a bigger bore. I have good brakes now, but I would like to have the pedal a little higher, now I understand the issue better, I think I can resolve it. LOL
 
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tubman said:
I can verify that a dual system should be well engineered and ideally, each circuit should be tested independently. I say this because of my experiences with a factory system. I have a "beater" '99 Ford F150 that I purchased new. Being in the Twin Cities area in the beginning of its life, it has encountered the usual rust problems, including brake lines. The first to go was one of the rear lines. While it was apparent that there was a problem, the truck was drivable and I was able to get to my shop with no problem and replace the rear lines. A quick bleed, and I was back on the road again.

A few years later, a front line rusted through and it was a completely different story. The brake system was so compromised that there was very minimum stopping power. Luckily, I was less than a couple of miles from my shop (which is on a county road out in the country) and was able to creep back to it. I replaced the front lines, and after a bleed, the brakes were back to normal. I was surprised by this because I did not expect the almost total failure unless something else went wrong.

Maybe it was a design problem on this particular model of truck, but ever since, I have lost the confidence I once had in dual systems.
Click to expand...


I do not recall any brake system design problems with any F-150 while performing D.O.T. partial system (Failed primary/secondary) stopping distance testing, part of the D.O.T. braking performance requirements. Stopping with rear brakes will result in much longer stopping distance vs front only braking, but is still a whole bunch better than loosing all braking!
 
V8 Bob said:
I do not recall any brake system design problems with any F-150 while performing D.O.T. partial system (Failed primary/secondary) stopping distance testing, part of the D.O.T. braking performance requirements. Stopping with rear brakes will result in much longer stopping distance vs front only braking, but is still a whole bunch better than loosing all braking!
Click to expand...

It would be futile to get into a detailed discussion of F150 brake systems. I think we can both agree that losing the front brakes will cause a serious degradation of brake performance; in my opinion a much larger degradation than most would expect. The point I was trying to make is that unless properly engineered, dual brakes are not the panacea most would expect. Just throwing a dual chamber master in will not necessarily provide true dual braking performance. One could just as well end up with no brakes at all on one part of the system if the other part fails.
 
V8 Bob said:
I do not recall any brake system design problems with any F-150 while performing D.O.T. partial system (Failed primary/secondary) stopping distance testing, part of the D.O.T. braking performance requirements. Stopping with rear brakes will result in much longer stopping distance vs front only braking, but is still a whole bunch better than loosing all braking!
Click to expand...

That's because the F150 would have been factory designed to have enough spare travel after the normal travel to ensure the non failed side would still work.
 
I think we should limit this particular discussion to include only those that have experienced a brake failure on this particular series of F150's.:rolleyes:

(Brake system analyses from reputable sources are also acceptable.)
 
Ron_r1959 said:
I think I would probably have liked to have a better understanding of the calculations involved before choosing a M/C . I may look for a M/C with a bigger bore. I have good brakes now, but I would like to have the pedal a little higher, now I understand the issue better, I think I can resolve it. LOL
Click to expand...


Ron ...... Just about the time you begin thinking that you understand the issue(s) better, you might want to re-think it all once again. Brakes is one very deep subject. You mention possibly looking for a M/C with a bigger bore. You must remember that increasing the diameter of the M/C bore will directly affect how much pressure that you need to push the brake pedal. Increasing the M/C bore will INCREASE the amount of foot pressure necessary to produce the same stopping power as before the change. You will likely be surprised at how much increased foot pressure will be required. Just one of the laws of hydraulics.

Coop


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V8 Bob said:
Gonna have to disagree with some of the above math.

1" master cylinder piston travels 1.27" for 1 c.i. of fluid movement.

1 1/16" master cylinder piston travels 1.12" for 1 c.i. fluid movement.

The 1" piston travel increase is .150", or just over 1/8", not 3/8". This results in pedal travel increase of .750" with a 5:1 ratio, or .9" with a 6:1. As I stated previously, using a 1" is doable in most cases with minimum effort. The resulting higher pressure output with a 1" works better with common disc/drum systems by slightly lowering the pedal effort.
I know converting to a dual master cylinder is the best hydraulic brake upgrade you can make, but does require some thought and extra effort.
Click to expand...

I agree. My mistake was in the .886
Should have been 1.130 to arrive at 1 ci of volume and then the piston travel difference of about an 1/8" (0.14) between the two master cylinders would have been evident.
 
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