Master cylinder swapability question ????

[kaptnkaos]

Hey Guys,

I haven't seen this question addressed...
My '68 CS has the old style master cylinder (it has two equal sized reservoirs).
The new replacement MC's have different sized reservoirs like the ones for disk brakes...
I have a good MC from the '71 that had disk brakes, but I have drum brakes on my '68.
I have all the stuff to swap over to disk brakes in the future, I want to rebuild the brakes and I beams first.
Can I use the disk brake MC I have with the drum brakes, or do I have to get a new one for drum brakes???

Thanks in advance
KaptnKA S

[Hawkrod]

If you have drum brakes you need a drum brake master cylinder. They make look the same but drum brake master cylinders have a residual pressure valve and disc brake ones do not (on the disc brake side). The residual pressure valve is important as it allows drum brakes to react immediately instead of having to be pumped up to overcome clearance. Because most of the vehicle braking is from the front wheels, losing that feature could be rated as life threatening! Hawkrod

[kaptnkaos]

Yeah, that's what I thought...

When I do the pwr disk upgrade I wanna replace the MC anyway...
The drum one I have is the old style and the top gasket leaks real bad...
I've not been able to find a replacement gasket for the old style top... I've tried everything to clean this one up, it's just to far gone.
I keep watching for one on ebay... and thought I had one, but someone out bid me by $.01 in the last second....

KaptnKA S

[FLATBEDFORD]

I bought a reman drum/drum MC for about $35 a couple years ago. There are a few for around $30 at www.rockauto.com . They have no listing for the gasket only.

[FLATBEDFORD]

I don't think this is a highjack.

On the swapability thing. I too plan on doing a disc brake upgrade. I have all the parts from a '77 F350. I plan to use the calipers, MC, and booster as cores only as I don't know how good they are.

1. Will a dent MC work with a '70 drum/drum booster?
2. If not, will a dent '77 booster and MC bolt in nicely in my '70?
3. Front discs were optional in '70, but the calipers are not the same as the '77 ones. Can I use a '70 disc/drum MC and booster with '77 calipers?
4. Are drum/drum and disc/drum MCs interchangeable?

[fordman]

1 yes
2 yes
3 yes
4 no

[kaptnkaos]

I just called Cut Rate Auto Parts, they can get me a rebuilt one for $30.
That isn't so bad... I musta been given the price for a new one 'cause I wuz thinkin' they were like $70-$80.
I didn't wanna pay that, then turn around and buy another one in a few months.
I wanna put new king pins, bushings, brakes and everything before I do the swap, but I wanna be able to use my truck in the meantime.

KaptnKA S

[FLATBEDFORD]

I don't think this is a highjack.

On the swapability thing. I too plan on doing a disc brake upgrade. I have all the parts from a '77 F350. I plan to use the calipers, MC, and booster as cores only as I don't know how good they are.

1. Will a dent MC work with a '70 drum/drum booster?
2. If not, will a dent '77 booster and MC bolt in nicely in my '70?
3. Front discs were optional in '70, but the calipers are not the same as the '77 ones. Can I use a '70 disc/drum MC and booster with '77 calipers?
4. Are drum/drum and disc/drum MCs interchangeable?

EDIT What a dummy! We just went through that! I meant to say.
4. Are drum/drum and disc/drum BOOSTERS interchangeable?

[fordman]

yes they are. the only thing about the booster that needs worried about is the year issue. it has to be a 77 1/2 or older to work. so 68-77 1/2 will work with disc or drums. all master cylinders will fit on all boosters. the dent master for drum drum will work with bump drum drum. a dent master from a disc drum will work with a bump disc drum.

[kaptnkaos]

Ok... now, I'm really confused

My booster is from the '71 CS w/disc/drum, but the MC is the stock (probably original) '68 drum/drum MC...
Bottom line... will a '71 disc / drum MC will work on my drum/drum set up or not ???

Edit: I just reread above and answered my question...

KaptnKA S

[willowbilly3]

I think I would check on that Master cyl. application. It doesn't seem like anything interchanges on the juice side, between the single piston and dual, rotors are different for sure and I think the pistons would displace differently, hence a different mc. The part store should ask.

[martinarcher]

I just bought a reman Bendix drum master cylinder at Advanced Auto Parts for my truck. It was $22. hard to beat that - I almost bought a spare.

[FLATBEDFORD]

I think I would check on that Master cyl. application. It doesn't seem like anything interchanges on the juice side, between the single piston and dual, rotors are different for sure and I think the pistons would displace differently, hence a different mc. The part store should ask.

That's what I'm thinking. Even though it may bolt up to the booster OK, there may be different pressure and volume requirements for the different calipers. I'd like to use the a new '77 MC, my current '70 booster, and new '77 calipers. Maybe I should spend the extra few bux and go with the newer booster too, but then don't I run into issues with the rod from the pedal to the booster?

[saidyene]

So I have a drum/drum power brake set up and I plan on going to disk/drum power brakes in the future. What can I reuse and what do I need to grab at the junk yard?

[kaptnkaos]

I think if you already have power brakes, you will only need the power disc MC, the distribution block, spindles and rotors...
possibly the hoses that connect to the calipers.
I'm not sure if the spindles are the same or not, so I included them...
I've heard that it is easier to replace the whole I-beam assembly ie: rotors, caliper etc. as a unit.
I've not done that yet, but have every thing I need to do it except the new stuff to rebuild the units prior to installation.

KaptnKA S