Power Booster & Master Cylinder Question
 

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.

Re: Power Booster & Master Cylinder Question
 

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.

Re: Power Booster & Master Cylinder Question
 

Thanks for the info Captainfab!

Re: Power Booster & Master Cylinder Question
 

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.

Re: Power Booster & Master Cylinder Question
 

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.

Re: Power Booster & Master Cylinder Question
 

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.

Re: Power Booster & Master Cylinder Question
 

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

Re: Power Booster & Master Cylinder Question
 

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.