Posted by David Sherman on Saturday, September 15, 2007 at 14:09:34 :
In Reply to: Master Cylinder posted by Matt in Md on Saturday, September 15, 2007 at 11:28:27 :
Have you gone through the brake system to at least make sure it works like it did when it was new? I don't think the stock brakes, in good condition, are that bad if you're driving at the speeds it was made for.
In my experience, all the old M37/PWs need their wheel cylinders and master cylinders rebuilt if they've never been done, and probably the hoses replaced as well. Have you pulled all the drums and looked to make sure the wheel cylinders don't leak, the shoes have plenty of lining left, and (most important) aren't soaked with oil from leaky axle seals? They also need to be adjusted, unlike modern self-adjusting brakes. A lot of old trucks have a "low pedal" just because the brakes haven't been adjusted in ages. If it's strictly a matter of the pedal slowly going to the floor, but when you check the brake fluid level in the reservoir it isn't loosing any, then the master cylinder is leaking. The rebuild kit is easy (napa part number 1), but you need to make sure the bore is smooth. Some rust and small pitting can be removed with a hone. I've done some fairly aggressive honing by using a drill press and lubricating the hone with brake fluid to wash the grindings away, but if the pits are too deep, you need a new MC or you need to get it lined.
It just seems to me that before you start trying to "improve" the original system, it might be good to first make sure the original system is working like it originally did.