how too calculate brake mastercylinder size

[brian wafer]

like title says i want too replace mastercylinder on my 1942 ford 2 ton truck. it has a 1 and a quarter size master cylinder now . i want too replace with a newer style double master cylinder for safty . they sell a cylinder and booster assembly for pickups but only 1 inch, would like to eliminate some trial and error!

 

[diesel4me]

Are you going to retain the original drum brakes?..if so,you'll need a master cylinder designed for drum brakes,ones for discs wont have a check valve that keeps a slight amount of pressure on the wheel cylinders to avoid excessive pedal travel...disc brakes have no check valve so the caliper pistons can retract without resistance..

Are you going to convert to power brakes?..not sure if your truck had the master cylinder under the floor,if so,thats a bigger challenge..
My brother has a 57 Studebaker truck that had that design master,he converted it to hydroboost brakes using a GM setup off a 1 ton...but he also has front and rear disc brakes ,he swapped a Firebird rear axle and a Nova front clip onto the original frame..

 

[Fordum]

Its not as simple as it seems.
Does your truck have the big remote vacuum booster on the frame? The volume it puts out would have to be figured also.

However before you worry about the smaller size, remember that the 1-1/4 master had to supply fluid to all four wheels.
Now, each side of the cylinder only supplies two cylinders.

If you know the diameter of the wheel cylinders and their maximum stroke, you can figure how much fluid they would require under worst case conditions.

Your best bet is to find a company who sells a system for doing that. I was going to convert my '67 F600, and found a company that said they sold kits, but I never went any farther.
No idea who the company was at this late date. I bought a new booster and stuck with what I have for now.

BTW, if you remove your booster, don't forget to plug the vacuum line. Darn truck will not run worth a darn if you forget........

 

[Fordum]

If its like my Ford, the master is on the firewall, with a really big remote booster under the frame.
You can mount a power booster and master combo in the original master's place without too much fabbing.
But it takes a lot of plumbing to split the system and bypass the booster.

But they might have put the master on the frame in '42, not sure.

 

[Greg72]

Check out the BillaVista article on Pirate4x4.

He goes into an EXTENSIVE discussion of braking systems, and the mathematics to calculate bore size, pedal effort and stroke length, etc.

As Fordum said, there's quite a bit to understand if you want the whole system to work perfectly..... and if you're mixing and matching parts, the odds of getting lucky and ending up with great brakes is pretty slim.


-G

 

[brian wafer]

thanks for your quick replies. master cylinder is frame mounted below floor. hydro vac is right behind master cylinder here,s a few pictures.

 

[brian wafer]

read quickly throught the bella vista article, quit interesting will read it over with a clear head. master cylinder is frame mounted below floor,hydro vac just behind master cylinder. the only reason i want too change the system is for the 2 compartment reservoir,incase a line would brake or a cylinder leak. tire chains can do a quick job.truck is not running yet need to go true an inspection first. i,ve put new rear wheel bearing and brakes and 1 and a half inch cylinders. front brakes will get done this winter with what ever master cylinder set up i use. so all new lines will be install, and it will be 4 wheel drum brakes. i want too use truck for hauling fire wood at least 2 cords a load so thats 10,000lbs,and its all in the mountains! well maybe start with 1 and a half cord!!!

 

[brian wafer]

i wont keep that box!!!