Which master cylinder ???

[copperhead_69]

Hi, I need a new M/C for my '72 F250 with power 4 wheel drums. It pours out fluid from the top even when I replaced the gasket. For the time being, I will flush and bleed the system completely and even try some hose clamps on the M/C. I plan to switch to disks when it warms up here in Colorado as I already have the complete setup from a '69 F250 waiting on the garage floor.

When researching a new M/C I keep finding a 1" bore and a 1 1/4" bore for the same '72 F250 with both power drums and power disks. Can I switch to a disk/drum M/C with my current drums or do I need to stay with a drum only M/C? My current M/C setup consists of the original brake booster with a Bendix M/C. What are the differences in a disk/drum M/C and 4W Drum M/C?
This truck is my DD and I am tired of not having the brakes I should.

-Scott

[sargentrs]

Your m/c should match your brake configuration. In my understanding, disc requires a different pressure/volume ratio than drum to achieve the same operating force therefore you should use a proportioning valve in the system to apply different volume to the disc than to the drum. 4 wheel drum will use the same amount of volume to all 4 wheels. I believe that's why the different size reservoirs in the m/c with the small reservoir relating to front disc and the larger reservoir relating to rear drum. At least that's the way I look at the braking system. More educated minds may chime in and explain it more technically.

[copperhead_69]

I have the M/C with different size reserviors. That's why I am confused and started the thread to begin with.
I am trying to find out if there is a difference between the M/C's even though they have the same reservoirs and operate on the same principles.

By the way sargentrs, I miss Georgia... I'm from Whitfield County, but I don't like to claim Dalton, GA. I am a "County Boy"

[sargentrs]

Hmmm. Maybe I'm wrong about that then. I don't know the technical differences between disc/drum and drum/drum but I do know their m/c's are different somehow. I'm with you on Dalton. I lived in Calhoun and Rome for over 10 years. Didn't realize how much I hated it until I moved to the N. Georgia mountains. I wouldn't live anywhere else now unless I go farther north when i retire. My boss has family in Colorado and his wife just bought them a house up there near them.

[copperhead_69]

Any one else have any info on master cylinders? I am holding off to see if anyone has any other input. Thanks in advance.

On a sour note: other than my brake issues, my alternator mounting bolt decided to break off in the block. Only a couple of threads was holding it up and I actually drove it the 12 miles to work and back. I found me a replacement grade 8 bolt (previous) was grade 5) and I have to tools to do the work, I just need the time. I should get it back on the road by this Sunday.

[Subzero]

I know a little about brakes with new(er) cars so I'll share what I understand to the best of my knowledge. A disc/drum setup requires different amounts of pressure to each kind of brakes ( drum vs disc). A metering valve will balance the different types of brakes by allowing the rear drums to build up a small amount of pressure first before the front disc so that the return springs in the drum can be overpowered. That allows all the brakes to apply at once evenly. As for the proportioning valve, that limits pressure to the rear brakes so they don't lock up ( as easily, now ABS has arrived). The different size reservoirs I thought were there as the rear system needs more fluid to span the distance but I might be wrong... Newer cars have just one reservoir thats a plastic case on top of the MC. I personally hate that design compared to the cast iron MC. I do know the manual vs power brake MC is thought.
Hope this helps

[ultraranger]

O'Reilly Auto Parts lists this MC for a '72 F-250 with power all-wheel drums:

http://m.oreillyauto.com/mt/www.oreilly ... &ppt=C0066