Power Booster & Master Cylinder Question

[apocalypse]

Hey Guys,
I'm going to add a power brake system to my Sub. I was planning on keeping the drum brakes all around. My question is do I still need to have the proportioning valve? I know I would need it, if I switched the front to disc, but since I'm not. I wasn't sure. If you guys could pass on that the expertise that you have, it would be great! Thanks in advance.

[Captainfab]

No you do not need a proportioning valve with drum/drums. The '67-'70 booster and master cylinder is what I recommend for use with a drum/drum system. That booster is compatible with my booster brackets also.

[apocalypse]

Thanks for the info Captainfab!

[apocalypse]

One more question on this guys. Does it matter what size booster I get, when swithing to power brakes? I'm looking at either 9" or 11" booster.

[Captainfab]

What size and type of booster will depend partly on how much vacuum your engine produces. The larger the diameter the more power assist you will get from a given vacuum. The same for a dual diaphram versus a single diaphram booster. And then there is hydroboost if the engine vacuum is just too low.

[apocalypse]

I have a 283 in the truck, so I'm not sure how much vacuum there is. Guess that's something I'm going to have to look into.

[Keith Seymore]

Originally Posted by Captainfab

No you do not need a proportioning valve with drum/drums. The '67-'70 booster and master cylinder is what I recommend for use with a drum/drum system. That booster is compatible with my booster brackets also.

Sidebar: So if you don't use the proportioning valve with drum/drum, do you still get the safety aspect of a split system? Does the master cylinder reservoir provide protection in the event of a leak in either the front brake lines or in the rear lines, without the shuttle portion of the prop valve?

I am contemplating updating the single pot m/c in my '63 Grand Prix to a dual system, which is why I ask.

K

[Captainfab]

I am not aware of a proportioning valve for the drum/drum brake system. Of course most of my knowledge is with the trucks. The '67-'70 trucks use what I call a distribution block. It is basically 2 ports in, 2 ports out.

My '68 Camaro with drums/drums has a similar distribution valve

To answer your question, if either the front or rear circuit were to develop a leak, there is no shuttle to shut off flow to that side. But you should still have limited braking ability to the other side.

Originally Posted by Keith Seymore

Sidebar: So if you don't use the proportioning valve with drum/drum, do you still get the safety aspect of a split system? Does the master cylinder reservoir provide protection in the event of a leak in either the front brake lines or in the rear lines, without the shuttle portion of the prop valve?

I am contemplating updating the single pot m/c in my '63 Grand Prix to a dual system, which is why I ask.

K