The Stovebolt Site Forums The Shop Area Driveline Anyone go from 1" to 1.125" MC Bore?

I bought a dual master cylinder a while back from one of the vendors that was stated as fitting 47-59. I was doing a little research today before I installed it tomorrow and see that my 1949 chevy 1/2 ton originally had a 1" bore. I am using the original Huck style brakes with new wheel cylinders. I understand that it will take more force to engage the brakes but will the 1 1/8" be practically usable with the original huck brake setup or will it require too much force? My truck was not operational when I got it and I have never driven an older vehicle so I have no idea the force that it takes.

Any experience or opinions are greatly appreciated.

Hy 1866yellowboy, the increase in bore size should cause no problems, do you know if the new master cylinder was designed for disc or drum or disc/drum brakes?

To be honest with you I am not sure 3B.

It is the one from classic parts of america.

http://www.classicparts.com/1947-59-Dual-Master-Cylinder/productinfo/71-201/#.VZIehflViko

I purchased it in a hurry a while back so that I could get into the free shipping price range when I was buying other things from them. I did not look as closely as I should have.

I see now that one port is a 9/16 and one port is a 1/2 inch so I am not sure which to run to the front and which to run to the rear or why they would be different. I have been reading about proportional valves and such but this is all new to me.

Looking up the part number it looks like the original application the master cylinder was made for was a four wheel disk brake car.

If you do the math, I think you will see that the force required for braking will be 27% greater than the original design.

The brake pedal pushing effort will increase because the master cylinder piston surface area will be larger.

Though the larger MC piston will increase the hydraulic pressure in the lines and at the wheel cylinders.

Now being the trucks use the same cab sheet metal, same transmissions, bell housings, chances are the brake pedals should be the same. So they will have the same mechanical leverage advantage. So if the only difference between the trucks is the MC piston dia. then your foot should not feel the difference. For the difference in MC piston size is for different weight rating of the truck models.

Thanks for all the input. Anyone use this master cylinder on their truck? Did you have to add 10 lb residual valves? Did you have huck brakes and how was the real life force with the 26% more input needed?

I changed to a larger bore MC on mine some time back, but not with huck brakes. I didn't notice any change in pedal pressure, but it did stop better. Having said that, I should add I rebuilt all the wheel cylinders and changed shoes, springs, etc at the same time. So it is hard to say if the MC was 100% the cause of the better stopping. About two years ago Rock Auto was offering the larger bore MC on a close out deal. I think they were $14 or $15, so I bought one for future use.
Jon

Is there any way to tell if a master cylinder has a residual valve build into it by appearance or an easy test? After reading some information it sounds like 10 lb residual valves are needed for drum brakes. Does the stock master cylinder have residual valves?

The residual valves are only needed if the master cylinder is below the wheel cylinders, they keep the fluid from returning to the master cylinder.

Smaller bore equals less volume with more travel to reach X amount of pressure at each wheel, where as, the bigger bore equals more volume with less travel to meet the same X amount of pressure. With that said, you should have just as much braking force requiring slightly more force on the pedal with slightly less pedal travel.

Joe

A bigger master cylinder bore will move more fluid so the pedal stroke will be shorter. It will also require more pedal effort to get the same braking effect because the line pressure exerted by the bigger piston will be less, not more than the smaller one develops.

Residual valves on drum brake wheel cylinders keep a little pressure against the tapered wheel cylinder cups to prevent air from being sucked past the cups as the master cylinder retracts. Since the brake shoes are spring-returned there will not be any drag on the drums even with 10 PSI residual valves. Disc brakes with that much residual pressure would drag all the time and overheat. 2 PSI residual pressure for discs, 10 PSI for drums, regardless of the position of the master cylinder.
Jerry

Hy Guys, if the master cylinder was designed for a disc/disc application then it will not have built in residual pressure valves. Residual pressure is required on drum brake applications regardless of where the master cylinder is installed relative to the wheel cylinders. As Hotrod Lincoln stated above 10 p.s.i. for drum brake residual valves, and for applications where the master cylinder is below the level of the disc brake caliper then a 2 p.s.i. residual valve is required. Residual valves were always installed in master cylinders for drum brake applications for the reasons Hotrod Lincoln stated above and because of that we never saw a separate valve, now most of the suppliers are supplying Corvette disc/disc master cylinders and it is up to the installer to install the correct components to have a safe, reliable, and properly functioning system, hope that helps.

Thanks for all of the information everyone. I can confirm that the master cylinder I have appears to be a corvette disc/disc master cylinder. Sticking a piece of small wire into the outlet port it appears to be clear all the way to the piston so I agree that there appears to be no residual pressure valve installed in this master cylinder.

I will be adding the 10 lb residual pressure valve in line with each of the outlet ports. I am going to keep the 1.125 inch bore master cylinder since I have already purchased it and see how the pedal feels.

Thanks again.