Are all Brake Master/Boosters Created Equal?
 

Looking for a replacement for my disc/drum 70 GTO. There are dozens of options on Ebay and elsewhere, 1-wire and 2-wire etc ranging from $115-300. Are they all created equal? I'll spend a little extra for the correct square master but not a fortune, and I'd rather have better-than-original operation than correct-appearing.

https://www.ebay.com/itm/68-72-gm-A-...oYSo:rk:1:pf:0

https://www.ebay.com/itm/Chevelle-Ca...cUT:rk:43:pf:0

What size bore would the original be?

Huh? They're not electric.

That'll be in the service manual you should buy.

My 67 uses two 'wires' to keep the cover on. Just saying. ;)

70 might use the square MC, so I dunno what's correct? :sorry:

I think the correct terminology is Wire Bail or just Bail

That's it

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Some people will flame me for promoting chinese junk but I have had good luck with CPP. I have used them on three cars. Never any installation issues and the one problem I had a new one was overnighted from California. They also have lifetime warranty to original owner.

I've had very good results with Pirate Jack over the years, boosters these days are a high fail-rate item.

https://piratejack.net/1964-1972-gm-...its/disc-drum/

Pretty sure OE for a Disc/Drum setup is 1 1/16 bore, but you can adjust for desired pedal feel.

If you're replacing both, you can consider going to a smaller booster, if you're not concerned with originallity. A 9" dual diaphram is a nice upgrade, gives room for tall valve covers, and a little extra boost, especially in lower vacuum situations.

If you run headers, and you did a make-shift relocation of the combo valve, order with a new valve and bracket, and the front line conversion kit. That will clean it up very nicely. You get a union, and a short length for the rear line, so you don't have to replace the whole rear line.

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Good info, thanks.

Is there any advantage to the Corvette design over the square design?

How can the cast-iron MC be kept looking new?

The vette ones are 'generic', and there usually isn't any cup/pin depth issues.

You can spray/coat the body with a coating of choice to prevent corrosion. You can wipe it down with acetone and spray it with as-cast engine paint, works pretty good.

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Eastwood Brake Grey is a good choice too, using their' prep recommendations:

https://www.eastwood.com/eastwood-br...y-aerosol.html

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I installed a 9" dual diaphragm booster with the corvette style master cylinder. The only issue I have with this setup is the extreme angle it places the booster at reduces the fluid volume since the reservoirs are half empty because of the angle. Come spring, I am going to replace the angle brackets (OEM style for 11" dia booster) with straight brackets.

My projects always get the G-Body Aluminum Master Cyls for best results, even 4-wheel disc.

Whatever angle the master cylinder is set at, needs to provide a straight pushrod angle to the brake pedal.

Master cylinders are typically tipped "up" in front to make a straighter pushrod angle to the pedal. Don't screw up that geometry just to gain some fluid capacity.

I agree with this, kinda. Needs further elaboration. Power masters are typically tipped up. Pushrod position on the pedal arm affects piston travel *and* leverage. Manual was level... used the higher hole. Power was angled, used the lower. At least as far as the A-bodies I'm familiar with.

But yeah, bad geometry is a no-no. If you're going to level it, you gotta know what youre doing.

So is running around with the front reservoir cover clamp disengaged because it rubs on the underside of the hood and a spongy pedal from pumping air into the brake system when braking after hard acceleration because the port in the bottom of the reservoir is momentarily uncovered.

1). Jack the back of the car up

2). Top off the master cylinder

3). Enjoy

There, fixed it for you.

Put air shocks on it and pump them up! Heheh!

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What's wrong with the makeshift conversion? And is there a good reason to go with a new attached prop valve? Besides the enjoyment of redoing all the lines instead of just swapping masters …

PJ website has no pics of that kit to see what's in it. Sorry the car is in storage so I can't recall exactly what the whole setup looks like.

This is where CPP shines. The prop valve is attached to the master and they give you a fitting to plug into your old junction block and splice into your rear brake line

Any "NEW" proportioning or combination valve is very suspect. They're Chinese Junk, subject to leakage of fluid out, or air in. When air leaks in, the brake pedal is low and squishy, but with no external traces to help diagnose. Judging by internet posts, they're unreliable. (I have zero direct experience with them because I use "good used" Genuine GM valves)

The 'make-shift' conversion leave the valve 'suspended', and not mounted to anything, and the lines are just however they reach.

The 'general' relocation is to use the bracket as shown in the attached pic, but there are several different types, so you need to ask when ordering which it is, and order the appropriate line kit.

It cleans up the lines, which are probably old and rusted, rounded off nuts from wrenches slipping, and sometimes even have the rock guard missing.

You don't have to rerun the line that goes to the rear brakes, if you don't want to, as 64Speed points out, and my comment in my original comment, you can get the $18 pre-bent line and fitting that connects to the rear line where the valve originally mounted.

The original front caliper runs do need to be re-routed too if you move the valve, and sometimes you have to add a short length. The one line for the driver's side is easy to replace, as is the passenger side, with the car on jack stands. That run that goes over to the passenger side is usually all beat up from previous services, and have seen many of them flattened.

So you can spend the time to do the 'make-shift' setup, and have it 'suspended', or add/bend existing lines, but it ends up looking like a spaghetti factory. By buying the $65 line kit, as I said, it cleans it all up nicely, and looks factory. You will probably save a lot of time too, because you don't have to 'figure' things out.

I've had good luck with the combo valves from Pirate Jack, who deal almost exclusively MBM Brake parts. MBM is in North Carolina, and they state they make all their' own parts:

http://mbmbrakes.com/about-mbm/

"We produce all of the parts you see here and would like the opportunity to serve you and your company.

John McLeod"

EDIT: The line kit also comes with valve to master lines as well.

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Working on a similar project on my 70 ragtop-I have an Inline Tube booster on it's way here, however a friend that has lots of experience with these set up has had multiple failures with the Inline Tube boosters. I am going to return the one that is headed my way and send a core to Booster Dewey in Oregon for a rebuild. Good Luck!