1 1/8 th inch master cylinder bore

[jimmijim8]

What would be the ramifications of using a clark fork lift master cylinder with a bore of 1 1/4 inch on a power drum brake equipped hawk? jimmijim

[ROADRACELARK]

Jimmijim,
You probably wouldn't notice much of any difference. If you did, it might require lighter pedal pressure to stop... the larger diameter piston will displace more fluid with the same pedal stroke. No big deal. I've seen this done on other makes of cars actually allowing the power brake booster to be removed.
Dan

[gordr]

quote:Originally posted by ROADRACELARK

Jimmijim,
You probably wouldn't notice much of any difference. If you did, it might require lighter pedal pressure to stop... the larger diameter piston will displace more fluid with the same pedal stroke. No big deal. I've seen this done on other makes of cars actually allowing the power brake booster to be removed.
Dan

Whoa, Dan!
All other things being equal, a larger bore size on the master cylinder will require greater pedal pressure, not less. And since the hydraulic pressure developed for a given amount of pedal force is a function of the AREA of the piston face, then it follows that pressure is proportional to the square of the piston radius.

E.G: double the bore size of the master cylinder, and you will have 1/4 the line pressure for the same degree of pedal effort. Halve the bore size, and you'll get four times the line pressure.

And since the volume of fluid delivered per unit distance of pedal travel follows that same square law, you can get into grief that way, too. Too small a m/c bore, and you will use up most of your pedal travel just getting the shoes out to the point where they meet the drums.

Getting to jimmijim's specific question, I believe it might work OK. Remeber Hawk power brakes are a Hydrovac system. The Hydrovac booster is a self-contained device mounted in-line between the master cylinder and the wheel brake units. If the Hydrovac is working properly, I expect the only thing you'd notice is a somewhat increased pedal pressure, and a somewhat shorter pedal stroke for the brakes to apply. The bore of the stock m/c is pretty close to 1", IIRC, so 1.25" isn't hugely bigger, but even so, the pressure difference is significant.

1" bore, radius=0.5", square=0.25 sq. in.
1.25" bore, radius=.625", square=0.391 sq. in. That's 60% more surface area on the piston, meaning 60% more pedal pressure to effect the same stopping power, and 60% less pedal travel before it firms up. (I left pi out, because it's a constant; radius is the only variable here.)

Me, if I had the Clark m/c on hand, I'd try it, just as an experiment. But I'd be VERY cautious about taking it on the road until I was comfortable with how the brakes worked in that arrangement. But if I were at the point of ordering a new master cylinder to replace a bad one, I'd stick with the stock size unless I had very good reason to be changing it.

Gord Richmond, within Weasel range of the Alberta Badlands

[jimmijim8]

Thanks for the replies guys. I knew I could count on some feedback. I am going to forego the 1 1'4 inch one only because of what has been said. It was a bargain at 30.00 but I want the brakes to work as they should. thanks jimmijim

[Guido]

Damn Gordon, you and Gary Ash must have been separated at birth. All this stuff is above my lowly B.A. degree in Political Science!

Guido Salvage - "Where rust is beautiful"

1946 M-16 fire truck
1948 M-16 grain truck
1949 2R16A grain truck
1949 2R17A fire truck
1955 E-38 grain truck
1957 3E-40 flatbed
1961 6E-28 grain truck
1962 7E-13D 4x4 rack truck
1962 Champ pickup
1962 GT Hawk 4 speed
1964 Avanti R2 4 speed
1964 Cruiser
And various other "treasures"

[studegary]

quote:Originally posted by Guido

Damn Gordon, you and Gary Ash must have been separated at birth. All this stuff is above my lowly B.A. degree in Political Science!

Guido Salvage - "Where rust is beautiful"

Don't feel bad Guido/Gary <G>. I have degrees in engineering and physics and worked as an engineer for 28 years and worked on Studebakers for the past 45 years, yet I am still amazed at these guys sometimes.

Gary L.
1954 Commander Starliner (restomod)
1959 DeLuxe pickup (restomod)

[garyash]

As a senior in college, back in the days when Studebaker was still making cars (just barely), I was working on a project which required a number of things to be made in the engineering school's machine shop. After I dropped the drawings off, I got a call from the head machinist to come down to the shop. Grabbing me by the ear and dragging me off to the rack where all the round stock was kept, he said, "See all this metal, son? I've got 1" round stock and I've got 1-1/2 round stock. So, if you want your parts made quickly, don't design them to be 1.03" diameter and ask me to waste my time making chips!" He was correct that I had just picked the numbers without thinking about how the parts would get made. It was a good and valuable lesson that all the theory in the world doesn't beat putting your eyes and hands on real steel, real tools, and asking questions of people who do these things all day for a living. The nice thing about SDC is that we can all team up with some good resources. I hope I never get too old to listen and learn.

Gary Ash
Dartmouth, MA
'48 M5
'65 Wagonaire Commander
'63 Wagonaire Standard

https://www.studegarage.com

[StudeRich]

Gord; I don't doubt that all your high-tech theory is correct, but how do you explain a vehicle like a Stude. truck: a 1/2 ton has a 1" M/C, a 3/4 ton has a 1 1/8" M/C, and a 1 Ton has a 1 1/4" in. to drive increasingly larger wheel cylinders and way bigger drums with much more weight, the pedal pressure seems the same, but are you saying nothing really changed proportionally, just actually requires more pedal pressure?[:0][:0]Rich.

quote:Originally posted by gordr

quote:Originally posted by ROADRACELARK

Jimmijim,
You probably wouldn't notice much of any difference. If you did, it might require lighter pedal pressure to stop... the larger diameter piston will displace more fluid with the same pedal stroke. No big deal. I've seen this done on other makes of cars actually allowing the power brake booster to be removed.
Dan

Whoa, Dan!
All other things being equal, a larger bore size on the master cylinder will require greater pedal pressure, not less. And since the hydraulic pressure developed for a given amount of pedal force is a function of the AREA of the piston face, then it follows that pressure is proportional to the square of the piston radius.

E.G: double the bore size of the master cylinder, and you will have 1/4 the line pressure for the same degree of pedal effort. Halve the bore size, and you'll get four times the line pressure.

And since the volume of fluid delivered per unit distance of pedal travel follows that same square law, you can get into grief that way, too. Too small a m/c bore, and you will use up most of your pedal travel just getting the shoes out to the point where they meet the drums.

Getting to jimmijim's specific question, I believe it might work OK. Remeber Hawk power brakes are a Hydrovac system. The Hydrovac booster is a self-contained device mounted in-line between the master cylinder and the wheel brake units. If the Hydrovac is working properly, I expect the only thing you'd notice is a somewhat increased pedal pressure, and a somewhat shorter pedal stroke for the brakes to apply. The bore of the stock m/c is pretty close to 1", IIRC, so 1.25" isn't hugely bigger, but even so, the pressure difference is significant.

1" bore, radius=0.5", square=0.25 sq. in.
1.25" bore, radius=.625", square=0.391 sq. in. That's 60% more surface area on the piston, meaning 60% more pedal pressure to effect the same stopping power, and 60% less pedal travel before it firms up. (I left pi out, because it's a constant; radius is the only variable here.)

Me, if I had the Clark m/c on hand, I'd try it, just as an experiment. But I'd be VERY cautious about taking it on the road until I was comfortable with how the brakes worked in that arrangement. But if I were at the point of ordering a new master cylinder to replace a bad one, I'd stick with the stock size unless I had very good reason to be changing it.

Gord Richmond, within Weasel range of the Alberta Badlands

StudeRich
Ferndale, WA