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10/29/16 8:08am - Original Message: 'Verifying Power Booster and Master Cylinder'
9TEEN72
Former Member
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Brick, NJ - USA

Vette(s):
1969 (2) - 1970 - 1972 - 1975 - 1989 - 1994 - 1996 - 1998 - 2003 - 2009 - 2011 - 2014

Joined: 10/17/2016
Posts: 15
I'm new to this forum but not new to Corvettes as I've had a few C3's - C4's  C5's and C6 & C7 Corvettes, but it's been a long time since I did a C3. I recently bought a 1972 Cpe that needs a lot of TLC and would like to know, before I jump into the engine compartment whether I have an original Master Cylinder and Booster. I had to leave on a 3 month trip the day after buying the car, and have minimal driving time in it, but one thing is for sure and that is there is a problem with the brakes. The previous owner "claimed" the calipers and pads were replaced, but I can't confirm if HE did it or the person he bought it from (he can't remember..Confused). The car stops but has a high pedal effort, so I think it's related to the booster, but whether it's a vacuum issue, or a check valve problem, or even just a bad booster, I did not have time to check. I want to draw up a work plan before getting home so I can approach the issues with the car in a proper format to get everything done before driving season gets back. I've tried asking questions on other Corvette related forums, but either don't get replies or I'm told to join and buy the NCRS judging guide. I had hoped that "asking questions" on a public forum would get me some answers, but as of yet, nothing has worked, can anybody help?

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10/29/16 9:05am - Reply: 'Re: Verifying Power Booster and Master Cylinder'
manchestershark Lifetime Member
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Equinunk, PA - USA

Vette(s):
1972 conv, 4-speed, 350, 200hp, numbers match, rally wheels, war bonnett yellow w/white top. good condition, nice driver.

Joined: 10/31/2007
Posts: 1898
You will NOT have trouble here on this site. The people here are MORE than happy to help out. You WILL get good answers. First, I would check for vaccume and the check valve. Do the easy stuff first. If there is a leak you should be able to hear it. Is there fluid in both reservoirs, are both ends of the car active, are the pads all touching the rotors. Rust builds up and does not allow the pads to operate correctly. Be best to re-build the entire system anyway, as the health of the car depends on the ability for it to stop. Others will chime in with better answers so be patient. Keep us in the loop.

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10/29/16 1:32pm - Reply: 'Re: Verifying Power Booster and Master Cylinder'
73shark
Standard Member
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Overland Park, KS - USA

Vette(s):
1973 Orange Metallic Coupe (orig owner), L82, 4 spd (WR), PS, (A/C & PW (I installed from wrecked 73)), leather, AM/FM Stereo, ran with '65 FI unit earlier & will again some day.

Joined: 7/9/2003
Posts: 394
Should properly bleed the brakes to eliminate the possibility that there's any air in the lines which can cause a soft pedal.  If the rivets in the rotors have been removed, then the TIR should be checked as an out of spec TIR will cause "pumping" which can suck air into the calipers.

The check valve can be easily checked w/ a hand held vacuum pump.


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1973 L-82 4 spd

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10/30/16 6:02am - Reply: 'Re: Verifying Power Booster and Master Cylinder'
9TEEN72
Former Member
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Brick, NJ - USA

Vette(s):
1969 (2) - 1970 - 1972 - 1975 - 1989 - 1994 - 1996 - 1998 - 2003 - 2009 - 2011 - 2014

Joined: 10/17/2016
Posts: 15
When I get back home I do plan on checking the calipers to make sure none of the pistons or pads are stuck from rust, as well as the vacuum source (and parts). My interest is in finding out if the master cylinder and booster are original because if they are then I'd have them repaired if either is the problem. I think something in the booster/vacuum system is the culprit as the only problem stopping the car is high pedal effort, and no spongy pedal. 

Thanks for the suggestions guys


|UPDATED|10/30/2016 4:02:50 AM (AZT)|/UPDATED|


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11/11/16 11:01am - Reply: 'Re: Verifying Power Booster and Master Cylinder'
Tooch1
Limited Member
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Vette(s):
1973 Convertible, L48, 4 Speed, PS, Numbers Matching, Mille Miglia Red, Dark Red Interior NCRS Top Flight Award Chapter/ June 2016

Joined: 11/29/2015
Posts: 47
It's easy to verify if your MC is original to the car. All 72 master cylinders were Delco Moraine semi gloss black, with two bleeder valves on the side. You have PB so the casting number should be 5480346. This should be cast on it. There should also be a two letter application code. For earlier cars it is located on the flat machine bossed area on the top front of the MC. Later 72's have it stamped in the area surrounding the front brake line fitting on the MC. (Really small and tough to see if MC is dirty or rusty.) That code will two letters followed the date code. Most Power brake cars should have the letters 'PG" stamped. Other 72's may also have 'MK' for power brakes and then finally really later 72-73 on will have TG. Bail handle white paper tags usually carried this same two letter broadcast code printed on them with red letters. BTW the 72's had the most different 2 letter broadcast codes of any of the 68-late 72. Some bail tags didn't match the stamped tags?? ( very confusing huh?) However, things in 73 settled down to just 'TG' for Power, and 'YA' for manual brakes. Hope this helps! Jimmy

|UPDATED|11/11/2016 9:01:47 AM (AZT)|/UPDATED|


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Tooch1 Pittsburgh Tri State Chapter NCRS Laurel Valley Corvette Club
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11/11/16 7:16pm - Reply: 'Re: Verifying Power Booster and Master Cylinder'
Pappy's Toy Gold Member
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WILLIAMSTOWN, KY - USA

Vette(s):
Silver Anniversary 1978, L82?, 4-speed

Joined: 12/5/2002
Posts: 130
I've had brake issues with my '78 and have ended up replacing all four calibers pads and while I was at it I replaced the flexible hoses. Now she stops fine.

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Pappy's Toy
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11/25/16 1:40pm - Reply: 'Re: Verifying Power Booster and Master Cylinder'
benzfxr
Limited Member
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Vette(s):
1982 crossfire

Joined: 9/19/2016
Posts: 2
Generally air in the system will present in a low brake pedal that gets higher if the brakes are pumped. 

A vacuum or booster problem will present in a hard to press pedal. 

With the engine off, pumping the brake pedal will empty the brake booster of any stored vacuum. then hold the brake pedal and starting the engine should cause the pedal the drop slightly. 

The must be full engine vacuum to the brake booster (15+ inches, check it with a vacuum/pressure gauge, they're not expensive) 

If there is enough vacuum, and the pedal does not drop as described, , suspect a booster problem . 




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____________________________________
Frank Scandura III President
Frank’s European Service, Las Vegas NV
Manager, Las Vegas Hybrids
Editorial Advisory Board, ImportCar Magazine

Author: How to Take Care Of Your Vehicle so it Will Take Care of You
Host, Frank’s Car Care Tips Radio Show
Independent Business Coach, Elite http://www.eliteworldwidestore.com/
Senior digital Shop Advisor and trainer for AutoVitals www.autovitals.com
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