Brake booster/master cylinder/prop valve - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**kev2809** · 11-14-2021, 10:20 PM

I bought this stuff new a while back and it got all rusted up and has zero miles. I plan on cleaning up the booster. but I need a new master cylinder. and also am wondering is a prop valve really needed? and if so, how would I know which to get?

truck has disc brakes up front with rear drums. does the year for the master cylinder make a difference? I believe mine is a 1" bore. but I really hate the locking metal bars on the lid

SCOTI · 11-15-2021, 12:13 PM

Prop valves are for safety as well as function once they were introduced. One can bypass them but you'll still need something to allow adjusting front & rear bias.

The fronts are usually 70% of the stopping force so something needs to be able to tune/adjust the rear. Factory prop valves are intended for factory applications (tire sizes). Once different tire sizes are used front & rear, the bias changes. Whether it's detectable or not is debatable & subjective.

Later model master cylinders will work so they don't have to be 'year model specific'. You'll want/need to use the proper bore size for the brake application. Manual brakes, power brakes, Hydraboost usually all require a different bore size. Bore size impacts pedal feel/force required. The plunger depth can also be different when using/mixing parts so you have to pay attention there as well.

My recommendation is to stick w/a kit if you aren't familiar w/this info already. Kits are usually based on a good combo of parts for a specific application.

**kev2809** · 11-15-2021, 12:39 PM

I read your info on the adjustable prop valves and that's probably the way I will go. I was digging around oreillys website and found the 73 master cylinder with the same 1" bore. I bought this stuff brand new from there and have no idea what route I went the 1st time.

I also have the 2002 tahoe booster and master cylinder assembly on my parts truck I could rob, but I haven't even started looking into that

68 P.O.S. · 11-15-2021, 08:56 PM

Food for thought...1-1/8" bore is normally for power brakes, but it seems some of these trucks did come with a 1" bore MC with PB. No idea what the difference would feel like between the 2.

**MikeB** · 11-15-2021, 11:09 PM

The stuff was new a while back, and then sat outside for 20 years?

**kev2809** · 11-16-2021, 07:55 AM

Quote:

Originally Posted by MikeB

The stuff was new a while back, and then sat outside for 20 years?

ha! just about. I put it on the truck about 7 years ago? maybe less. I never put a coating on it. I rolled the truck out the garage and I got burnt out and didn't work on it much. drove it down the street once. so I pulled everything back off to actually paint it (front frame, suspension, etc.). the booster seems fine, but the master cylinder rusted inside too where the holes are. I don't trust it.

**kev2809** · 11-16-2021, 07:57 AM

Quote:

Originally Posted by 68 P.O.S.

Food for thought...1-1/8" bore is normally for power brakes, but it seems some of these trucks did come with a 1" bore MC with PB. No idea what the difference would feel like between the 2.

the problem is this stuff I pulled off, I bought it brand new from oreillys. I just don't remember what the hell I bought back then (as in what application I told them). I'm really thinking I told them 73 c10, because that's what my pads and rotors are for

SCOTI · 11-16-2021, 10:33 AM

Quote:

Originally Posted by kev2809

the problem is this stuff I pulled off, I bought it brand new from oreillys. I just don't remember what the hell I bought back then (as in what application I told them). I'm really thinking I told them 73 c10, because that's what my pads and rotors are for

Prop valve would likely be 71-72 since it appears to be one of the units that's mounted next to the master cylinder. The Squarebody generation prop vale was moved to the front lower splash-shield between the rails in front of the motor.

I would imagine 71-72 for the vacuum booster unless it has an integral mounting bracket (71-72's don't; 73-up do).

Master cylinder could be from any early model but again I'd guess 71-72 because of the cap retainer clips & for disc brakes.

68 P.O.S. · 11-16-2021, 09:31 PM

Your combination valve looks like the Bendix 411, which was stock for these trucks.

Your MC is a newer "universal" model that works for disc/drum or disc/disc applications. Will work fine on your truck.

I have no idea on the booster. Looks right tho.

**kev2809** · 11-16-2021, 11:14 PM

the 72 master cylinder is listed as a 1.13 bore...I used some cheapo HF calipers and I got 1.10. so I think the 72 is spot on. I don't see anything "bendix 411" though

**kev2809** · 11-17-2021, 08:15 PM

these are the brackets for the booster

SCOTI · 11-17-2021, 11:11 PM

Quote:

Originally Posted by kev2809

these are the brackets for the booster

Those are the 67-72 adapter brackets for the vacuum booster.

**kev2809** · 11-20-2021, 11:07 PM

ya I'm pretty confident I went 72 booster, cylinder, and prop valve.

thanks scoti

11-14-2021, 10:20 PM	#1
kev2809 low n' slo Join Date: Mar 2009 Location: rosenberg, texas Posts: 5,174	Brake booster/master cylinder/prop valve I bought this stuff new a while back and it got all rusted up and has zero miles. I plan on cleaning up the booster. but I need a new master cylinder. and also am wondering is a prop valve really needed? and if so, how would I know which to get? truck has disc brakes up front with rear drums. does the year for the master cylinder make a difference? I believe mine is a 1" bore. but I really hate the locking metal bars on the lid Attached Images __________________ 67 1/2 ton Suburban - Project DRGNWGN. Build thread -_--_--_ _________ _--_-_ -/____\|__\|__\__ ,.,,,.,.,,.,\|_O _______ O_]

11-15-2021, 12:13 PM	#2
SCOTI Registered User Join Date: Apr 2001 Location: DALLAS,TX Posts: 22,064	Re: Brake booster/master cylinder/prop valve Prop valves are for safety as well as function once they were introduced. One can bypass them but you'll still need something to allow adjusting front & rear bias. The fronts are usually 70% of the stopping force so something needs to be able to tune/adjust the rear. Factory prop valves are intended for factory applications (tire sizes). Once different tire sizes are used front & rear, the bias changes. Whether it's detectable or not is debatable & subjective. Later model master cylinders will work so they don't have to be 'year model specific'. You'll want/need to use the proper bore size for the brake application. Manual brakes, power brakes, Hydraboost usually all require a different bore size. Bore size impacts pedal feel/force required. The plunger depth can also be different when using/mixing parts so you have to pay attention there as well. My recommendation is to stick w/a kit if you aren't familiar w/this info already. Kits are usually based on a good combo of parts for a specific application. __________________ 67SWB-B.B.RetroRod 64SWB-Recycle 89CCDually-Driver/Tow Truck 99CCSWB Driver All Fleetsides @rattlecankustoms in IG Building a small, high rpm engine with the perfect bore, stroke and rod ratio is very impressive. It's like a highly skilled Morrocan sword fighter with a Damascus Steel Scimitar..... *Cubic inches is like Indiana Jones with a cheap pistol.*

11-15-2021, 12:39 PM	#3
kev2809 low n' slo Join Date: Mar 2009 Location: rosenberg, texas Posts: 5,174	Re: Brake booster/master cylinder/prop valve I read your info on the adjustable prop valves and that's probably the way I will go. I was digging around oreillys website and found the 73 master cylinder with the same 1" bore. I bought this stuff brand new from there and have no idea what route I went the 1st time. I also have the 2002 tahoe booster and master cylinder assembly on my parts truck I could rob, but I haven't even started looking into that __________________ 67 1/2 ton Suburban - Project DRGNWGN. Build thread -_--_--_ _________ _--_-_ -/____\|__\|__\__ ,.,,,.,.,,.,\|_O _______ O_]

11-15-2021, 08:56 PM	#4
68 P.O.S. Registered User Join Date: Jan 2007 Location: Puyallup, WA Posts: 1,662	Re: Brake booster/master cylinder/prop valve Food for thought...1-1/8" bore is normally for power brakes, but it seems some of these trucks did come with a 1" bore MC with PB. No idea what the difference would feel like between the 2. __________________ 72 C10 lwb fleetside -stock 350/350 combo

11-15-2021, 11:09 PM	#5
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,597	Re: Brake booster/master cylinder/prop valve The stuff was new a while back, and then sat outside for 20 years? __________________ Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, recent AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then!

11-16-2021, 09:31 PM	#9
68 P.O.S. Registered User Join Date: Jan 2007 Location: Puyallup, WA Posts: 1,662	Re: Brake booster/master cylinder/prop valve Your combination valve looks like the Bendix 411, which was stock for these trucks. Your MC is a newer "universal" model that works for disc/drum or disc/disc applications. Will work fine on your truck. I have no idea on the booster. Looks right tho. __________________ 72 C10 lwb fleetside -stock 350/350 combo Last edited by 68 P.O.S.; 11-23-2021 at 11:53 AM.

11-16-2021, 11:14 PM	#10
kev2809 low n' slo Join Date: Mar 2009 Location: rosenberg, texas Posts: 5,174	Re: Brake booster/master cylinder/prop valve the 72 master cylinder is listed as a 1.13 bore...I used some cheapo HF calipers and I got 1.10. so I think the 72 is spot on. I don't see anything "bendix 411" though __________________ 67 1/2 ton Suburban - Project DRGNWGN. Build thread -_--_--_ _________ _--_-_ -/____\|__\|__\__ ,.,,,.,.,,.,\|_O _______ O_]

11-17-2021, 08:15 PM	#11
kev2809 low n' slo Join Date: Mar 2009 Location: rosenberg, texas Posts: 5,174	Re: Brake booster/master cylinder/prop valve these are the brackets for the booster Attached Images __________________ 67 1/2 ton Suburban - Project DRGNWGN. Build thread -_--_--_ _________ _--_-_ -/____\|__\|__\__ ,.,,,.,.,,.,\|_O _______ O_]

11-20-2021, 11:07 PM	#13
kev2809 low n' slo Join Date: Mar 2009 Location: rosenberg, texas Posts: 5,174	Re: Brake booster/master cylinder/prop valve ya I'm pretty confident I went 72 booster, cylinder, and prop valve. thanks scoti __________________ 67 1/2 ton Suburban - Project DRGNWGN. Build thread -_--_--_ _________ _--_-_ -/____\|__\|__\__ ,.,,,.,.,,.,\|_O _______ O_]



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