What's the difference in a pb master cylinder vs. manual ? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

red69ss · 12-03-2011, 06:09 PM

like the title says is there a diff. between a power brake mc vs. a manual? This is on a 72 chevy if that makes a difference. I had a guy tell me he took a pb booster and just pulled a manual mc forward and added the booster and it worked with some tweeking to the rod that hooks to the pedal. just wondering if anyone knows of a diff. thanks

Ackattack · 12-03-2011, 07:05 PM

The bore of the piston are different sizes

JimKshortstep4x4 · 12-03-2011, 08:25 PM

All of the manual master cylinders that I have seen have a very deep tapered hole in them to keep the rod in place. The manual rod has a tapered end to fit the manual master cylinder. I am not sure how you would be able to match the manual rod to the booster or match the booster to the tapered hole in the manual master cylinder.

Jim

Longhorn Man · 12-04-2011, 12:10 AM

I pulled the master off my blown booster and bolted it directly to the firewall.
i have been told that in these year of trucks they have the same p/n power or manual. I don't know if it is true, however, I have seen plenty of people on here pull the master cylinder off the firewall and slip a booster in there, and roll with it trouble free.

68gmsee · 12-04-2011, 12:41 AM

There's no difference. On my 68 I pulled the master cylinder forward and installed a booster. Several year later the booster went bad and I took it off and rebolted the m.c. back to the original position. I bought a booster last month and again just pulled the m.c. forward and reinstalled the booster.

I did the same on my 69 when I converted it to p. brakes. From what I've noticed the only difference is in the drum/drum vs. disc/drum master cylinders.

**jocko** · 12-04-2011, 01:43 AM

Can't speak for all years, but can speak to a 67 drum/drum setup (so my A$$umption is that it's common across all 67-72 drum/drum setups...). Anyhoo, the Non-power drum/drum master was different from the 67 power drum/drum master - the manual had the deep hole in the back of the piston vice the shallow one that fits the booster's intermediate pushrod. Yes, possible to go FROM power to manual with the same master - the opposite is not true in a bolt-on fashion - will take some modificaiton of the interface/intermediate push rod between the booster and master.

screamin_c10 · 12-04-2011, 01:44 AM

Quote:

Originally Posted by 68gmsee

There's no difference. On my 68 I pulled the master cylinder forward and installed a booster.....

I did exactly the same thing, just needed to lengthen the warning light wire a bit....

red69ss · 12-04-2011, 08:59 AM

wow thanks for all the great replies! it sounds like it is deffinently a possibility so I'm going to try it. it will be a couple of weeks before I can try it I have to get the truck home first , but I'll let yall know my experience with it . thanks

68gmsee · 12-04-2011, 01:57 PM

Quote:

Originally Posted by jocko

... Yes, possible to go FROM power to manual with the same master - the opposite is not true in a bolt-on fashion - will take some modificaiton of the interface/intermediate push rod between the booster and master.

Yeah, some modifications are required. I did have to adjust the push rod on the booster to m.c. out some, change out the brake pedal pushrod and adjust the brake light switch.

Quote:

Originally Posted by screamin_c10

I did exactly the same thing, just needed to lengthen the warning light wire a bit....

Mine was a little tight but just long enough.

dmack91 · 12-05-2011, 03:53 AM

Mine bolted straight in with no adjustments that I recall. Works great. 68 Drum/drum.

SS Tim · 12-05-2011, 04:30 AM

Its worth remembering that Power Brakes were also offered as a dealer installed accessory. My '69 list shows two kits, one for C,K10 and another for C20-30,K20.

609thomasm · 12-05-2011, 11:30 PM

Some manual brake master cylinders have a residual pressure check valve. This should not be used with disc brakes. The valve is behind the brass seat that the line seals against in the port. I had a 67 camaro in the late 80's that I installed disc on the front and removed the valve in the port for the front. I have heard that these were stop being used sometime in the early 70's.

12-03-2011, 06:09 PM	#1
red69ss Burnouts are therapeutic Join Date: Jun 2007 Location: lancaster, south carolina Posts: 852	What's the difference in a pb master cylinder vs. manual ? like the title says is there a diff. between a power brake mc vs. a manual? This is on a 72 chevy if that makes a difference. I had a guy tell me he took a pb booster and just pulled a manual mc forward and added the booster and it worked with some tweeking to the rod that hooks to the pedal. just wondering if anyone knows of a diff. thanks __________________ 1969 CHEVELLE SS 1972 C10 ALMOST DAILY DRIVER 1968 C10 RUSTBUCKET (MISSION IMPOSSIBLE) 1972 PONTIAC LEMANS CONVERTIBLE (WIFE'S CAR) "My wife and I were happy for twenty years. Then we met." - Rodney Dangerfield "The difference between genius and stupidity is that genius has its limits." - Einstein

12-03-2011, 07:05 PM	#2
Ackattack Senior Member Join Date: Aug 2002 Location: Valley Center KS Posts: 3,524	Re: What's the difference in a pb master cylinder vs. manual ? The bore of the piston are different sizes __________________ Project Bruiser: 68 Pro-Touring C-10 5.3L / 4L60E Project Ironhide: 97 GMC Crew Cab 4x4 Cummins SOLD: '69 GMC 1/2T SWB TBI'd: Project No Buck Assembly Manual Index Sign up Thread!!! Factory Service Manual Index

12-03-2011, 08:25 PM	#3
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	Re: What's the difference in a pb master cylinder vs. manual ? All of the manual master cylinders that I have seen have a very deep tapered hole in them to keep the rod in place. The manual rod has a tapered end to fit the manual master cylinder. I am not sure how you would be able to match the manual rod to the booster or match the booster to the tapered hole in the manual master cylinder. Jim __________________ 1971 Shortbox step side 4x4, 350 sbc, 3:07 rear end 1965 Impala SS 400 sbc, Muncie rock crusher 1966 Impala SS 396 bbc, TH 400 1969 El Camino, 350 sbc, TH 350 1971 Snowplow built on a Blazer frame 1972 GMC Short bed, stepside, TH 400, 427 BBC

12-04-2011, 12:10 AM	#4
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Re: What's the difference in a pb master cylinder vs. manual ? I pulled the master off my blown booster and bolted it directly to the firewall. i have been told that in these year of trucks they have the same p/n power or manual. I don't know if it is true, however, I have seen plenty of people on here pull the master cylinder off the firewall and slip a booster in there, and roll with it trouble free.

12-04-2011, 12:41 AM	#5
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	Re: What's the difference in a pb master cylinder vs. manual ? There's no difference. On my 68 I pulled the master cylinder forward and installed a booster. Several year later the booster went bad and I took it off and rebolted the m.c. back to the original position. I bought a booster last month and again just pulled the m.c. forward and reinstalled the booster. I did the same on my 69 when I converted it to p. brakes. From what I've noticed the only difference is in the drum/drum vs. disc/drum master cylinders.

12-04-2011, 01:43 AM	#6
jocko Senior Member Join Date: Oct 2009 Location: Godley, TX Posts: 17,975	Re: What's the difference in a pb master cylinder vs. manual ? Can't speak for all years, but can speak to a 67 drum/drum setup (so my A$$umption is that it's common across all 67-72 drum/drum setups...). Anyhoo, the Non-power drum/drum master was different from the 67 power drum/drum master - the manual had the deep hole in the back of the piston vice the shallow one that fits the booster's intermediate pushrod. Yes, possible to go FROM power to manual with the same master - the opposite is not true in a bolt-on fashion - will take some modificaiton of the interface/intermediate push rod between the booster and master.

12-04-2011, 08:59 AM	#8
red69ss Burnouts are therapeutic Join Date: Jun 2007 Location: lancaster, south carolina Posts: 852	Re: What's the difference in a pb master cylinder vs. manual ? wow thanks for all the great replies! it sounds like it is deffinently a possibility so I'm going to try it. it will be a couple of weeks before I can try it I have to get the truck home first , but I'll let yall know my experience with it . thanks __________________ 1969 CHEVELLE SS 1972 C10 ALMOST DAILY DRIVER 1968 C10 RUSTBUCKET (MISSION IMPOSSIBLE) 1972 PONTIAC LEMANS CONVERTIBLE (WIFE'S CAR) "My wife and I were happy for twenty years. Then we met." - Rodney Dangerfield "The difference between genius and stupidity is that genius has its limits." - Einstein

12-05-2011, 03:53 AM	#10
dmack91 Registered User Join Date: Jan 2011 Location: Redmond, OR Posts: 763	Re: What's the difference in a pb master cylinder vs. manual ? Mine bolted straight in with no adjustments that I recall. Works great. 68 Drum/drum. __________________ 68 Chev C20- son has it now 83 K20 - bought from son 70 C20 - in progress

12-05-2011, 04:30 AM	#11
SS Tim Registered User Join Date: Aug 2010 Location: Edwards, CA Posts: 7,503	Re: What's the difference in a pb master cylinder vs. manual ? Its worth remembering that Power Brakes were also offered as a dealer installed accessory. My '69 list shows two kits, one for C,K10 and another for C20-30,K20. __________________ Thanks, Tim * VIN/Model Decoders * Power Team Charts (engine/transmission/gear ratio) * Post Your Pickup SPID Blazer SPID Suburban/Panel SPID * RTFM ... Read The Factory Manuals... download 'em here Highlanders Do you have a 1972 Plaid Pickup? Plaid Blazer ** Plaid Suburban

12-05-2011, 11:30 PM	#12
609thomasm Registered User Join Date: Sep 2011 Location: Conway, SC Posts: 26	Re: What's the difference in a pb master cylinder vs. manual ? Some manual brake master cylinders have a residual pressure check valve. This should not be used with disc brakes. The valve is behind the brass seat that the line seals against in the port. I had a 67 camaro in the late 80's that I installed disc on the front and removed the valve in the port for the front. I have heard that these were stop being used sometime in the early 70's.

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