Drum master cylinder question.

[two-bit]

Hey all,
I got into the flatbed today to move it around so i could do some snow moving. When i stepped on the brake pedal, whoosh, down to the floor it went.
So I'm thinking bad line, whatever.
So i check it out, can't find a leak anywhere
So i go back and check the master cyl. Bingo.
For some reason the master is pumping all the fluid from the rear res. into the front and overflowing it. I figure its a bad seal in the master.

My usual parts place is already closed, so i check around with a few other places. The three places i called all told me that the master cylinders from all F-350's crossed over from '79 to '68 for power brake units.

Hoqwash i say. They all say, "according to the computer", so i asked about the different size brake lines, does the new master come with an adaptor to hook up to my lines...
I get "according to the computer"

I ask about the pressure differences between the disc/drum master and a drum/drum master...
Again i get "according to the computer"

RRRRRRRR.

Correct me if i am wrong....please.
But as far as i know, you cannot use a disc/drum master on drum/drum brakes.
If you do, you will blow out the front wheel cylinders.

Aren't the front brake line fittings different between the two masters different to keep this from happening?


Nothing like owning an old truck that the computer jockeys think are all the same.

RRRRRRRRR

Two-bit

[Wes]

no there is a check valve in drum/drum master cylinder. Disc/drum MC doesn't use.

[FORDification]

That's true, you can't use a disc/drum MC with a drum/drum setup. Using one will cause your rear brakes to lock up way too early, but it won't blow out the front wheel cylinders.

However, you said

...The three places i called all told me that the master cylinders from all F-350's crossed over from '79 to '68 for power brake units...

You said they told you "power" brakes...you CAN use a master cylinder from a power drum set-up. There's no difference in MC's between power or manual brakes.

[two-bit]

Thanks Kieth,
I thought i was right about the drum/drum vs. disc/drum thing.
Yeah it would be the rears, cause the front res. feeds the rear and the rear res. feeds the front.

I never thought about before. The power-manual thing. HHMM, something to remember.

Maybe if i feel really lucky i'll go look for a rebuild kit on Monday

Two-bit