dual master cylinder

[1948F-1Pickup]

The movement increase is about 3/8" at the master when comparing the larger bore master of 1 1/16" and the greater amount of piston movement with the smaller bore master of 1 inch. (0.866" piston travel in the 1 1/16" bore to move 1 cubic inch of brake fluid vs 1.27" piston travel in the 1" bore to move 1 cubic inch of brake fluid)

With that extra 3/8" AND the pedal ratio, you might very well bottom the brake pedal into the floorboard on some vehicles/applications.
It wasn't a problem on my '48 truck but it just underscores that you wouldn't know the true story unless you did the math.

[V8COOPMAN]

Originally Posted by 1948F-1Pickup

The movement increase is about 3/8" at the master when comparing the larger bore master of 1 1/16" and the greater amount of piston movement with the smaller bore master of 1 inch. (0.866" piston travel in the 1 1/16" bore to move 1 cubic inch of brake fluid vs 1.27" piston travel in the 1" bore to move 1 cubic inch of brake fluid)

With that extra 3/8" AND the pedal ratio, you might very well bottom the brake pedal into the floorboard on some vehicles/applications.
It wasn't a problem on my '48 truck but it just underscores that you wouldn't know the true story unless you did the math.

That's interesting that you actually took the time to calculate the additional travel required of the M/C's piston to displace the necessary volume of brake fluid. My main concern was to make it obvious to folks that may not be familiar with what we're talking about here, as well as the POSSIBILITIES of what can happen if you're not aware.

The math that I am seeing here doesn't tell the ENTIRE story. If you subtract 0.866" from 1.27", that leaves an ADDITIONAL distance of 0.404" that the PISTON must travel. That is not the main concern. You must also take pedal travel into account. This means that the pedal pad (the part that your foot pushes on) must travel a GREATER distance which is dependent on the pedal ratio. Pedal ratio involves the difference in the distance of the pushrod pivot pin from the pedal-pivot centerline vs. the distance that the pedal pad is from the pedal-pivot centerline. If the pedal footpad is five (or more) times farther from the pedal pivot point, the pedal RATIO is 5:1. That means that the pedal PAD must be able to travel FIVE TIMES the ADDITIONAL DISTANCE that the piston must travel. In this case, we're talking about an additional 2.02" PEDAL TRAVEL.

BEWARE.....as this does NOT INCLUDE any additional pedal travel necessary as I referenced ABOVE because of a leak in one side of the system. All that I am suggesting here is that it should be wise to induce a "test leak" in each side of your newly-plumbed brake system to insure that you still have full-stroke-pedal capabilities should a leak develop in either side of your system. Also beware that "full stroke" means WITHOUT THE M/C BOTTOMING-OUT. The M/C should NOT bottom-out.

Coop


.

[1948F-1Pickup]

Originally Posted by V8COOPMAN

The math that I am seeing here doesn't tell the ENTIRE story. If you subtract 0.866" from 1.27", that leaves an ADDITIONAL distance of 0.404" that the PISTON must travel. That is not the main concern. You must also take pedal travel into account. This means that the pedal pad (the part that your foot pushes on) must travel a GREATER distance which is dependent on the pedal ratio. Pedal ratio involves the difference in the distance of the pushrod pivot pin vs. the distance that the pedal pad is from the pedal's pivot centerline. If the pedal footpad is five (or more) times farther from the pedal pivot point, the pedal RATIO is 5:1. That means that the pedal PAD must be able to travel FIVE TIMES the ADDITIONAL DISTANCE that the piston must travel. In this case, we're talking about an additional 2.02" PEDAL TRAVEL.

BEWARE.....as this does NOT INCLUDE any additional pedal travel necessary as I referenced ABOVE because of a leak in one side of the system. All that I am suggesting here is that it should be wise to induce a "test leak" in each side of your newly-plumbed brake system to insure that you still have full-stroke-pedal capabilities should a leak develop in either side of your system. Also beware that "full stroke" means WITHOUT THE M/C BOTTOMING-OUT. The M/C should NOT bottom-out.

Coop


.

That is true..... hence my mention of "that extra 3/8" AND the pedal ratio.
Almost any re-designer of a brake system should be looking at total stroke
available for the pedal assembly and comparing it to total stroke available
of the master. Few people do this, that is why few people should be modding
brake systems.

[V8 Bob]

Originally Posted by 1948F-1Pickup

The movement increase is about 3/8" at the master when comparing the larger bore master of 1 1/16" and the greater amount of piston movement with the smaller bore master of 1 inch. (0.866" piston travel in the 1 1/16" bore to move 1 cubic inch of brake fluid vs 1.27" piston travel in the 1" bore to move 1 cubic inch of brake fluid)

With that extra 3/8" AND the pedal ratio, you might very well bottom the brake pedal into the floorboard on some vehicles/applications.
It wasn't a problem on my '48 truck but it just underscores that you wouldn't know the true story unless you did the math.

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.

[V8COOPMAN]

Originally Posted by V8 Bob

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.

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



.

[1948F-1Pickup]

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Originally Posted by V8 Bob

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.

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.