Slanted ones:

'65 Dart 270 /6:

I'm putting off the major brake upgrade and sticking with the 9" drums, for now. But I've got to get rid of that stupid single-system master cylinder.

I see a lot of posts dancing around this question, without ever really asking it explicitly, so: How can I, a drum-brake kind of guy, use a dual system disc-brake M/C?

I could get a new unit and adapters from Ma Mopar and bolt it right in. Add some steel brake line and some different distribution blocks and I'm done. But will I blow out the front cylinders?

And this alleged residual pressure valve - I've never seen one on this car, and it's from the era when the valve was external, mounted in the line at the master. Not there, and the brake line is a neat fit - nothing's been removed. I've had the old cylinder apart - nothing in there, just straight out to the brake line.

When I got the car, I replaced the wheel cylinders with generic rebuilt ones, so they MAY be of the newer kind that don't need the valve. How will I know?

And if all else fails, where am I likely to find an all-drum M/C for my A-body?

Thanks!

I have a 1974 prop valve/metering block for sale (I think I listed it on here a few weeks back). You'll probably want a 1970's drum brake dual pot master cylinder (both reservoirs are equal sizes, the disk brake one has a smaller front reservoir), and do a little bit of plumbing.

someone who has done this kind of conversion will hopefully chime in and tell you what the 'speedbumps' are, it really isn't that tough, the hard part is making sure your brakes are applying correctly/proportioned right.

-D.Idiot

If you're sticking with 4 wheel drums then just use a dual master cylinder from a 4 wheel drum car. Hit the wrecking yards and pull the MC and distribution block from a later model car and bolt it in there.

I would not recommend the use of a disc/drum MC if you don't have disc/drums. The factory engineers got paid big bucks to sort these combinations out, leverage their knowledge.

Edk,

Where are you located? I have a '74 Dart MC for 4-whl drums that you can have for free if you want it. It was a rebuilt unit I bought in 1998, and it was working when I pulled it off. Don't have the prop valve, though.

I agree with DI and Andyf's statements - use an all-drum MC and prop until you swap to discs. The factory prop valve could just be replaced with some tee fittings and an adjustable prop valve (Summit - $40) in the rear line too.

Lou

_________________
Home of Slant6-powered fun machines since 1988

In an offline exchange, Lou (the gracious, invaluable, and tastefully trim-level equipped Dart270) offered to drop the part off at my house while he was in town (!), then told me to check for a rebuild at the parts store. In 5 minutes www.napaonline.com sold me a '68 all-drum MC for $22 + $11 core. I guess I'm used to digging for pre-67 parts, and forgot that post-67 parts are like mushrooms.

Does anybody know about problems at this point? I remember something about the shaft length being longer on later cars, causing the brakes to overheat?

And what about the prop. valve? The MC is built to deliver the right proportion of hydraulic pressure to the front and rear drums. Is it really a warning light switch? Or is is doing something I don't quite get?

Strangely enough, NAPA stocks rebuilt single-system MCs for the '65. Personally, I think that should be illegal - only resto shops should deal that death trap, and then only with a signed promise that the car never hits the street.

I'm doing the same swap.

For the Proportioning valve, I put a plug in where the rear line exits the single MC proportioning valve.

I am then running the rear line from the Duel MC through a Summit adjustable valve. I am not on the road yet, but can’t think of any reason this will not work.

The pushrod went into the new MC with no problem. Use the new pushrod retaining sleeve that should have come with the new MC. I had to adjust the brake light switch.

Good luck,

John

The use of a prop valve on a drum/drum car is an interesting question. You actually do not need one since all four drums should have the same braking force/pressure response curve. The factory didn't put prop valve on drum/drum cars as far as I know. They used a distribution block in the early years and then added a warning switch in later years. I do not recall ever seeing an actual prop valve on a drum/drum car but maybe real late model cars did end up with such a thing.

Anyway, what I'm trying to say is that you most likely do not need a prop valve if you are using drum brakes at all four corners. You don't even need a distribution block if you don't want to run a warning light. Just run a T fitting in the front line and run the rear line direct.

That's what I was beginning to suspect - the front-rear bias is built-in to the brakes themselves, based on the slave cylinder sizes, rotor area, etc. If they got all their calculations right, I should be set. And if I lock up one end of the car, I can always tune up the bias with the famous Summit valve.

And why would I need a warning light anyway? I think I would know if the brakes were failing without needing an idiot light?

Thanks, slantheads

I'm using that basic thought on my setup. I added the Prop valve for my future enhancement/upgrade to disk brakes.

John