[Interceptor]

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?

[Schurkey]

Originally Posted by Interceptor

1-wire and 2-wire etc

Huh? They're not electric.

Originally Posted by Interceptor

What size bore would the original be?

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

[242177P]

Originally Posted by Schurkey

Huh? They're not electric.

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

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

[OG68]

I think the correct terminology is Wire Bail or just Bail

[Interceptor]

Originally Posted by OG68

I think the correct terminology is Wire Bail or just Bail

That's it

Sent from my SM-G930W8 using Tapatalk

[64speed]

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.

[HWYSTR455]

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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[Interceptor]

Originally Posted by HWYSTR455

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?

[HWYSTR455]

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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[HWYSTR455]

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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[NeighborsComplaint]

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.

[Half-Inch Stud]

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

[Schurkey]

Originally Posted by NeighborsComplaint

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.

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.

[242177P]

Originally Posted by Schurkey

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.

[NeighborsComplaint]

Originally Posted by 242177P

But yeah, bad geometry is a no-no.

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.

[Keith Seymore]

Originally Posted by NeighborsComplaint

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.

1). Jack the back of the car up

2). Top off the master cylinder

3). Enjoy

[NeighborsComplaint]

Originally Posted by Keith Seymore

1). Jack the back of the car up

2). Top off the master cylinder

3). Enjoy mopping up the spilled brake fluid from the overflowing reservoirs

There, fixed it for you.

[HWYSTR455]

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

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[Interceptor]

Originally Posted by HWYSTR455

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.

.

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.

[64speed]

Originally Posted by Interceptor

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