what master cylinder to use

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what master cylinder to use

Postby 434monza » Mon Feb 16, 2009 10:47 pm

what master cylinder and prop. valve is everybody using with the s10 front brakes setup,,,also i want to stay with manual brakes
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Re: what master cylinder to use

Postby v8astregt » Mon Feb 16, 2009 11:45 pm

I used one from like a 76 Caddy. Don't remember the model, but I don't think there were too many variations that year. My car stops great with it. I also run a Wilwood adjustable proportioning valve. I've got S10 brakes all around.
75 Pontiac Astre GT: 406SBC/TH350, roll bar, S10 goodies, down to 11.47 so far, more to come later.
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Re: what master cylinder to use

Postby norcalace » Tue Feb 17, 2009 12:57 am

'76 caddy MC here too. I also have a Monza power brake booster. Generic GM style prop valve. Make sure to get a disk/drum or disk/disc depending on your setup.
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Re: what master cylinder to use

Postby cosvega76 » Tue Feb 17, 2009 11:20 am

With the single-piston S-10 front calipers and rear drum brakes, I used a Monza master (7/8" bore) and adjustable proportioning valve for the rear.

Chuck
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Re: what master cylinder to use

Postby pobrien327 » Wed Feb 25, 2009 10:01 pm

I did the s10 conversion with the stock monza master cylinder. I have terrible brakes. I have bled them several times.. it is that when I press down, very little happens. I read I should go to the s10 master which has a smaller bore.. and then I need a power brake booster that fits it.

Bob Grumm never talked about this!!! :(
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Re: what master cylinder to use

Postby cosvega76 » Thu Feb 26, 2009 10:54 am

Which brakes are you using, front and rear (single or dual piston calipers, rear brake size, wheel cylinder bores)? Do you have a firm pedal? Is it high or low? Which Monza master are you using? '75 Monzas used the Vega front calipers, so they used the small (3/4" bore) Vega master, '76-'80 used the larger bore master. S-10s use a 24mm bore master, which is close to a 15/16" bore. Did you bench bleed the master before installing it?

Too small of bore master will give you a low, spongy pedal, too large will take an enormous amount of pedal pressure to achieve acceptable braking performance.

Chuck
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Re: what master cylinder to use

Postby Yenkoboy » Thu Feb 26, 2009 11:10 am

Before you get all sad that Bob Gumm didn't give you enough info. You need to look at your problem. I had a buddy 2 years ago do what you did with no problems. Changes to your brakes can bring out weak parts or workmanship, double check your work rebleed if no better replace parts.

Good Luck Mark
72 GT Vega aka "Little Evel" 22K Miles V6 3.8 T5 5 speed and 7.5 4.10 Posi
72 GT Vega aka " Little Evel II (Jegster Chassis)
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Re: what master cylinder to use

Postby v8astregt » Thu Feb 26, 2009 7:59 pm

That's the nature of building a brake system from scratch. My Astre worked awesome from day 1. I didn't even entirely bleed the system from the start. Meanwhile, my Edsel has 4wdb, and a Corvette M/C. I've bled each wheel 5 times and I get NOTHING. Been messing it with it for two years.
75 Pontiac Astre GT: 406SBC/TH350, roll bar, S10 goodies, down to 11.47 so far, more to come later.
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Re: what master cylinder to use

Postby pobrien327 » Thu Feb 26, 2009 9:14 pm

Yes, I bench bled the 3 different masters I tried.. and each time I bled all four corners... I am 55 and have been working on cars on and off for 42 or so years. I have rebuilt engines/trannys- manual and automatics/ and several rear ends... I could change points and condenser/set dwell and timing before I could drive.... So assume I have "some" background

The pedal is firm - very firm - right in the middle to upper part of the travel. There is not much stopping power.. I have to be very careful because it just won't stop very fast.. I can't lock the brakes at any speed..

I used new stock s10 calipers, pads, and rotors.... so do I need to get the smaller bore s10 master and vacuum can? Have other people had this problem? The rears are all new stock monza drums and shoes....

Any help is appreciated guys !
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Re: what master cylinder to use

Postby porschekilla » Thu Feb 26, 2009 9:46 pm

Sorry for jumpin in with my own question but what proportioning valve should be used with s10 discs up front and caddy discs out back? thanks
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Re: what master cylinder to use

Postby Yenkoboy » Thu Feb 26, 2009 10:31 pm

Why don't you start a new thread and where work on you problem. Because we have Highjacked this post. If you have a Vega with a Monza MC you do need a Prop Valve.

Sorry for the Highjack Mark
72 GT Vega aka "Little Evel" 22K Miles V6 3.8 T5 5 speed and 7.5 4.10 Posi
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Re: what master cylinder to use

Postby 283vega » Fri Feb 27, 2009 7:47 am

Check your gm manual on this system.It may require that you push in and hold a button on your proportioning valve while bleeding the brakes.They state this is nescesary if you have replaced lines or wheel cylinders or the like.I have the same problem with my brakes as your describing and this is the part or place I ran in to trouble.Once it warms up I'll get back to it and rebleed as the manual says.
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Re: what master cylinder to use

Postby cosvega76 » Fri Feb 27, 2009 12:46 pm

It sounds like you have a master cylinder with too LARGE of bore already. What diameter is it? I currently have a one-inch bore master in my Vega right now, and it takes a healthy leg to get the car to stop quickly. Was your car a manual or power brake car to begin with? If it was power originally, you will need to move the pin for the push rod on the pedal up to the hole closer to the pedal pivot. This will give you a more favorable pedal ratio for manual brakes.

Chuck
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