Vacuum Source for Power Brakes & Other Questions

I have read most of the old posts re power brakes and have never seen the answer to this: stock engine, power brakes; what's the best place for vacuum? I suspect I could tie into the egr valve below the carb but am not sure. Second ques.: I'm not satisfied that I have the definitive answer to whether or not I can use a master cylinder from a wagoneer ('80) that has front disc brakes. I pulled the booster and master cylinder from the truck and can use the whole thing if it's safe. HELP? Still would like to get measurements or drawings for brackets for a powersteering pump for the 230. Thanks for all the help.

you can. You might have to fiddle w/an aftermarket proportioning valve, which is no big deal.

egr valve? huh, wha, where, huh?

Get a cheap, like $22, 1977 non power corvette master and bolt it on your booster. No proportioning valve needed...plenty of fluid moved.

whuh? 77 Vettes didn't have power brakes???????????

prop vave just to keep the rears from locking up, I meant. If he's got the master and booster from a FSJ, fire it up!

You'd be miles ahead to get a drum/drum master cylinder or as Spicer suggested, the disc/disc one. The disc/drum cylinder typically has two different residual pressure valves inside.

Chris

Lucky: I think you might be mistaken on that one. The residual pressure valve, if any, is usually in the factory proportioning valve on the frame. The master cylinders usually just have different sized bores for each piston if memory serves me correctly. I just went out and looked at the setup on the bench, out of a 78 GMC 3/4t truck...

Scratch "EGR": sub "positive crankcase ventilation" valve. I am a "newbie" afterall. LOL

What I've been told/learned is that the RPV is in the master cylinder, usually behind the inverted flare fitting. Drum/drum gets a pair of 10 pounders, disc/drum gets one of each or just a 10 lb on the drum circuit and disc/disc probably gets none.

According to MasterPower, the "proportioning" valve - actually a combo valve - has 2 functions:
Metering or holdoff to apply the rears just barely sooner than the fronts to stop straight and level
Proportioning to control the pressure rise to the rears to keep from locking up.

Personally I don't like the idea of using an OEM combo valve on anything other than the original application since the brake bias is set up for a specific brake characteristic. With the adjustable ones you can dial in exactly how hard you want the rears to come on.

Chris

Chris: I agree. Custom is better but not as 'easy'. I'm going to go w/manual 4whl disc master and whatever else I need after that.

I ordered the Corvette MC from NAPA. Re vacuum source: suggestions? I would appreciate a note from anyone who has actually installed a divorced 205, using stock everything else: send a name and I'll contact them.

i have a system from a suburban with disc/ drum rear , would that work good ? i have the complete donor sitting in my drive way waiting to be hauled to the junkyard . do i need to pull off any other parts ?

so BDial:What you would like to know is:
1)Where do you get the Vacuum source for the Power Brake Booster?(on a Stock 230 Tornado)
2)And can you use a Power Brake Booster/Master Cylinder from a 1980
FSJ with Disc/Drum? or do you have to use a proportioning valve with it?
Also does anyone have measurements or drawings for brackets for a powersteering pump for the 230?
These are fine questions that I too would like definitve answer to.
Why a Corvette (non-power) Master cylinder?

I think the Corvette M/C because it is a common disc/disc set-up, whereas most others are disc/drum. The disc/disc should provide same proportioning F-R to our drum-drum setup.

Drum vs disc brakes require vastly different volume and pressure to operate - thus suing a disc/drum M/C would throw off the front-to-rear bias ,whereas the disc/disc should maintain a close-to-normal bias.

I think that is the logic behind it.

so a Disc/Disc Master Cylinder with a Power Booster is a Better set-up than a Drum/Drum Master Cylinder with a Power Booster?(for a stock wheeled 715)

I believe that Spicegear is the one the started the '77 Corvette master cylinder thing. If I remember right, he went to a parts store and was looking through the available mc's. He was looking for the largest piston diameter he could get. He can tell you the exact size. The '77 Corvette with out power brakes had the largest diameter mc cylinder and it was made for a disc/disc system. That means that no proportioning valve is needed. They also fit the AMC booster and most GM boosters. They are easy to find new and cheap. I think he paid around $30.00 for his new.

If you can find a dual mc that is drum/drum with the same size pistons as the Corvette, it will be exactly the same performance. Adding a booster just makes it less pedal effort.

Sorry for jumping into your business Spicegear, but I figured you needed a rest from explaining this every two weeks.

I been reading this thread with great interest. I too am planning to upgrade the breaks on my Kaiser. I called a local brake shop who referred me to a good custom brake shop in Southern, CA who specializes in Hot Rods, CH Topping company. http://www.chtopping.com/Home/
They have a bunch of tech articles and offer a brake drum venting service which is supposed to keep drums cool. In the articles, this venting will give drums the same performance as disc setups, without the expense.
Check it out.

Drums will stop a vehicle as good as disc when cold. They will heat up and you get brake 'fade'. Disc heat up also, but not as much and with not as much fade. If you are going to drive your truck at slow speeds or mostly highway, I wouldn't worry about vented drums. Doing crash stops in traffic every day will motivate you to change something.

Late '60's and early '70's Buicks had some cool finned aluminum drums. They still faded in stop and go traffic.

Driving style has a lot to do with how good your brakes work.

If I were shopping for a drum/drum cyl. I would ask for one from a 69 chevy 20 or 30 series pickup and I think it will work with jeep booster. Spicer, I looked at a non power vette cyl and the pushrod hole was waaaaay too deep . It is made that way so rod won't slip out of cyl. Booster rod would not start to engage cyl. I got one for power brake vette with shallow pushrod hole. works with j-20booster. I don't know what is different from your setup.

Spicer extended his pushrod by an inch or an inch and a half...forget which...and that makes up the difference.
brute4c

i would suggest not going with a disc/drum master cylinder when you have other better options available. i have a master cylinder/booster from an 89 wagoneer. it gives me trouble all the time. i dont have a proportioning valve, but i always have problems with rears locking up, then fronts locking up, uneven application, ect... after learning about the 77 'vette master cylinder i am inclined to swap it right in as soon as i get home.

-BrianM