School me on master cylinders - The 1947 - Present Chevrolet & GMC Truck Message Board Network

C15_Sierra · 01-19-2012, 11:40 PM

My '80 has manual brakes, and I want to convert them to power brakes to better complement the 5.3

I got a used '84ish booster and master cylinder that has all sorts of rust/nasty crud in the forward (front?) compartment. Rear is relatively clean.

First, is the master salvageable? Can I take it apart/clean it, or is already FUBAR? Is it recommended to try and repair?

Second, if I go the "just replace it" route, LMC lists a whole bunch of master cyls for trucks with power brakes. I'm guessing my plain jane Sierra came with the smallest brakes (SPID doesn't mention any upgraded brakes), at 11", does that refer to drum diameter? Should I match the master cylinder to the booster (like I said, '84ish but I can't be certain, I didn't pull the part from the truck) or should I match it to my '80 chassis? What are the differences?

Thanks!

Also..side note - there's a connector that has been cut off (probably by me when I was doing the motor swap) at the proportioning valve. What is that originally for?

willett · 01-20-2012, 01:24 AM

I believe that you can get rebuild kits for MC's but its not something that is often done in this day and age.

Most people just replace the mc when it gets tired.

11" should be drum diameter.

ghettoluxury · 01-20-2012, 01:38 AM

Take the 84'ish master to the parts store and get a new one usually around $20. It should be direct swap for the lines, if not you can pick up adapters at your local parts store.

S10Fan · 01-20-2012, 06:43 AM

You'll also need to change the pedal rod and pedal rod angle.

BTW, I wouldn't install used brake parts, turn in the old stuff as cores and install new parts.

Forgot to add......you may find it necessary to change the rear wheel cylinders as well. Some of the part numbers/applications are different between a power and manual brake setup.

C15_Sierra · 01-20-2012, 08:34 AM

Thanks for the tips, guys.

I already have the pedal rod and bracket, so those aren't not a problem.

I just checked LMC for part # compatibility and it looks like the cutoff year was '84 for the wheel cylinders. Otherwise, the same for all 2WD 1/2 tons 74-84. They don't differentiate between power and manual brakes

01-19-2012, 11:40 PM	#1
C15_Sierra Registered User Join Date: Apr 2011 Location: Hartford CT Posts: 223	School me on master cylinders My '80 has manual brakes, and I want to convert them to power brakes to better complement the 5.3 I got a used '84ish booster and master cylinder that has all sorts of rust/nasty crud in the forward (front?) compartment. Rear is relatively clean. First, is the master salvageable? Can I take it apart/clean it, or is already FUBAR? Is it recommended to try and repair? Second, if I go the "just replace it" route, LMC lists a whole bunch of master cyls for trucks with power brakes. I'm guessing my plain jane Sierra came with the smallest brakes (SPID doesn't mention any upgraded brakes), at 11", does that refer to drum diameter? Should I match the master cylinder to the booster (like I said, '84ish but I can't be certain, I didn't pull the part from the truck) or should I match it to my '80 chassis? What are the differences? Thanks! Also..side note - there's a connector that has been cut off (probably by me when I was doing the motor swap) at the proportioning valve. What is that originally for? __________________ -Steve 1980 GMC C15 Sierra LWB Dark Carmine Red/Carmine Int Was: 250/3spd (1980-88), then a 305/TH350 (1988-2011) Now: 5.3/4L60E, 2.73 12-bolt open rear

01-20-2012, 01:24 AM	#2
willett Another Day, Another Dollar Join Date: Nov 2008 Location: North Vancouver, BC Posts: 1,316	Re: School me on master cylinders I believe that you can get rebuild kits for MC's but its not something that is often done in this day and age. Most people just replace the mc when it gets tired. 11" should be drum diameter. __________________ -78 K20 Cheyenne 454 long box, 4" lift, 35" MT's, '84 cab, '80 box "its hip to be square"

01-20-2012, 01:38 AM	#3
ghettoluxury Registered User Join Date: Apr 2009 Location: Waynesfield Ohio Posts: 1,991	Re: School me on master cylinders Take the 84'ish master to the parts store and get a new one usually around $20. It should be direct swap for the lines, if not you can pick up adapters at your local parts store. __________________ 1949 Five Window, 1973 Step Side, 2000 Z71

01-20-2012, 06:43 AM	#4
S10Fan Old Heap Driver Join Date: Mar 2008 Location: Newport News, Va Posts: 2,642	Re: School me on master cylinders You'll also need to change the pedal rod and pedal rod angle. BTW, I wouldn't install used brake parts, turn in the old stuff as cores and install new parts. Forgot to add......you may find it necessary to change the rear wheel cylinders as well. Some of the part numbers/applications are different between a power and manual brake setup. __________________ _____________________________ Bryan '99 Silverado 1500, 4.3, 5-speed, reg cab, short bed '50 Chevy 2DR Hard Top, 350/350, M2 Front End, 3:08 gear, cruiser. '40 F*d Sedan, all Chevy power, Heidt's front end, TCI rear, nice driver. Last edited by S10Fan; 01-20-2012 at 06:45 AM. Reason: additional info*

01-20-2012, 08:34 AM	#5
C15_Sierra Registered User Join Date: Apr 2011 Location: Hartford CT Posts: 223	Re: School me on master cylinders Thanks for the tips, guys. I already have the pedal rod and bracket, so those aren't not a problem. I just checked LMC for part # compatibility and it looks like the cutoff year was '84 for the wheel cylinders. Otherwise, the same for all 2WD 1/2 tons 74-84. They don't differentiate between power and manual brakes __________________ -Steve 1980 GMC C15 Sierra LWB Dark Carmine Red/Carmine Int Was: 250/3spd (1980-88), then a 305/TH350 (1988-2011) Now: 5.3/4L60E, 2.73 12-bolt open rear

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