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pete rad
Senior Member
Joined: 29-November-2014
Location: usa
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Points: 305
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Posted: 28-August-2021 at 4:10AM |
This will cause the brake pedal to be pulled towards the floor.
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pete rad
Senior Member
Joined: 29-November-2014
Location: usa
Status: Offline
Points: 305
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Posted: 28-August-2021 at 7:52AM |
A weak or broken spring inside of the brake booster might also be the problem. When the spring is working properly it keeps the brake pedal up at all times especially while the engine is running, and at cruising speeds when there is high engine vacuum. So the brake pedal does not get pulled down towards the floor.
Edited by pete rad - 28-August-2021 at 8:10AM
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kychevyguy
Senior Member
Joined: 16-December-2013
Location: Lexington KY
Status: Offline
Points: 1996
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Posted: 28-August-2021 at 8:31AM |
pete rad wrote:
A weak or broken spring inside of the brake booster might also be the problem. When the spring is working properly it keeps the brake pedal up at all times especially while the engine is running, and at cruising speeds when there is high engine vacuum. So the brake pedal does not get pulled down towards the floor.
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The brake pedal will return back up IF the engine is off though....
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JT, USAF Ret./Architect 1971 Ford F100 "Lizzy" 1971 Cougar XR7 "Kitty" 1984 Chevy Silverado "Sylvia" 2009 Smart Fortwo Cabrio "Lil Dude" 2015 Volvo XC60 R-Design "Sven"
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kychevyguy
Senior Member
Joined: 16-December-2013
Location: Lexington KY
Status: Offline
Points: 1996
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Posted: 28-August-2021 at 9:14AM |
I am currently searching YouTube for ways to verify if the booster is good...
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JT, USAF Ret./Architect 1971 Ford F100 "Lizzy" 1971 Cougar XR7 "Kitty" 1984 Chevy Silverado "Sylvia" 2009 Smart Fortwo Cabrio "Lil Dude" 2015 Volvo XC60 R-Design "Sven"
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kychevyguy
Senior Member
Joined: 16-December-2013
Location: Lexington KY
Status: Offline
Points: 1996
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Posted: 29-August-2021 at 12:29PM |
Okay, there are a few different things that can be checked for bad booster, as an example, I have included a concise short video here:
Test #1: While the engine is off, pump the brake pedal 4 times, holding the brake pedal down on the last pump. Start the engine. If the pedal sinks, the booster is good. When I do this test, the pedal immediately sinks when I start the engine.
Test #2: Start the car and after it has idled for a couple minutes, press and hold the brake pedal down. Shut off the engine. The brake pedal should wait a moment and then start to push back to your foot. When I do this test, the pedal does not move at all for about 7/8 seconds before it starts to slowly pushing my foot back up.
Test #3: Start the engine and let idle for a couple minutes, then turn off the engine. Pump the brake pedal about 3 times to see if it gets harder to push each time. This tests the reserve vacuum in the booster. When I do this test, the first brake pedal pump goes down easily, but the second pump and third are much harder to press.
My conclusion is that the booster might be good??? As a brainstorm, is it possible that my engine is not pulling enough vacuum? If I put a vacuum gauge on here, am I looking for 12-18lbs of vacuum? I found in our technical articles vacuum diagrams of 72 and 73 models, but no 76 cars... Maybe I just eliminate some emissions crap here....? (required: 1. Brake booster, 2. PVC, 3. transmission, 4. vacuum advance on distributor, 5. HVAC controls inside?)
Signed, Still frustrated in Kentucky
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JT, USAF Ret./Architect 1971 Ford F100 "Lizzy" 1971 Cougar XR7 "Kitty" 1984 Chevy Silverado "Sylvia" 2009 Smart Fortwo Cabrio "Lil Dude" 2015 Volvo XC60 R-Design "Sven"
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72 RS 351
Senior Member
Joined: 04-September-2014
Location: Knoxville TN
Status: Offline
Points: 2765
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Posted: 30-August-2021 at 1:00AM |
I thought you already had replaced the booster? I'd do the rear wheel cylinders, that sounds possible given all the rest.
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Don 73 Ranchero "Sport 72 front end", floor shift/console, planning EFI 7000+ rpm 351-4V &4R70W 73 Ranchero GT 351C-4V &4R70W for sale later. 92 Lincoln Mark VII SE GTC, OBDII 347/4R70W
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handsofstone
Senior Member
Joined: 13-April-2018
Location: Northeast
Status: Offline
Points: 3941
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Posted: 30-August-2021 at 4:05AM |
My booster vacuum line goes directly to the base of the carb. 3/8" i.d. hose.
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kychevyguy
Senior Member
Joined: 16-December-2013
Location: Lexington KY
Status: Offline
Points: 1996
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Posted: 30-August-2021 at 11:03AM |
72 RS 351 wrote:
I thought you already had replaced the booster? I'd do the rear wheel cylinders, that sounds possible given all the rest.
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I can not get a new booster in the current market, and simply can't afford to have mine rebuilt, so I got a replacement booster from someone on here. It was in their garage and although he thought it was a working one, he was not for sure. His is the current booster that is installed on my car. I replaced the rear wheel cylinders this past Saturday.
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JT, USAF Ret./Architect 1971 Ford F100 "Lizzy" 1971 Cougar XR7 "Kitty" 1984 Chevy Silverado "Sylvia" 2009 Smart Fortwo Cabrio "Lil Dude" 2015 Volvo XC60 R-Design "Sven"
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kychevyguy
Senior Member
Joined: 16-December-2013
Location: Lexington KY
Status: Offline
Points: 1996
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Posted: 30-August-2021 at 11:04AM |
handsofstone wrote:
My booster vacuum line goes directly to the base of the carb. 3/8" i.d. hose. |
I think that is what they did in 1972. Mine is a 76, and the booster vacuum line goes from the booster to a "tree" mounted on the firewall.
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JT, USAF Ret./Architect 1971 Ford F100 "Lizzy" 1971 Cougar XR7 "Kitty" 1984 Chevy Silverado "Sylvia" 2009 Smart Fortwo Cabrio "Lil Dude" 2015 Volvo XC60 R-Design "Sven"
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Big Bird
Senior Member
Joined: 25-August-2013
Location: New York
Status: Offline
Points: 4194
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Posted: 30-August-2021 at 11:12AM |
Check that tree for damage or leaky hoses leading elsewhere.
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"What we do in full frontal view, is more honest than your cleaned-up mind." Randy 1979 T-Bird 2005 F-150 STX RCSB 4.6, 3.55 LSD How the Heck does a REGULAR CAB SHORTBED weigh over 5200 pounds?
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handsofstone
Senior Member
Joined: 13-April-2018
Location: Northeast
Status: Offline
Points: 3941
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Posted: 30-August-2021 at 11:49AM |
How much vacuum does your engine produce? Curious.
Is this something that originally just happened overnight?
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kychevyguy
Senior Member
Joined: 16-December-2013
Location: Lexington KY
Status: Offline
Points: 1996
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Posted: 30-August-2021 at 4:38PM |
handsofstone wrote:
How much vacuum does your engine produce? Curious.
Is this something that originally just happened overnight?
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I am also wondering the same thing. I am assuming that 12-18lbs is what I should be looking for...? When I bought the car about a month ago, the brakes were an issue then. The previous owner did not know what the problem was and is not mechanically inclined.
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JT, USAF Ret./Architect 1971 Ford F100 "Lizzy" 1971 Cougar XR7 "Kitty" 1984 Chevy Silverado "Sylvia" 2009 Smart Fortwo Cabrio "Lil Dude" 2015 Volvo XC60 R-Design "Sven"
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californiajohnny
Moderator Group
Joined: 05-October-2013
Location: winlock, wa
Status: Offline
Points: 14606
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Posted: 30-August-2021 at 9:39PM |
not lbs... actually in. of Hg ( inches of mercury) but most are around 30 at idle connect a vacuum gauge and see what it reads??? should be steady , if it fluctuates rapidly would indicate a burnt valve a little movement but low could be a big cam...
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JOHN 74 GRAN TORINO S&H CLONE 74 VETTE CUSTOM 90 S10 BLAZER 4X4 LIFTED 77 CELICA CUSTOM 75 V8 MONZA SUPERCHARGED 79 COURIER VERT. SLAMMED 75 VEGA V6 5 SPD 70 CHEV C10 P/U 68 MUSTANG FB CONVERSION
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handsofstone
Senior Member
Joined: 13-April-2018
Location: Northeast
Status: Offline
Points: 3941
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Posted: 31-August-2021 at 3:28AM |
See if auto parts olace has an ele tric vacuum pump and use it only on the booster and see if that does it. Make sure you don't go too high. It should be fine with 18.
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kychevyguy
Senior Member
Joined: 16-December-2013
Location: Lexington KY
Status: Offline
Points: 1996
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Posted: 02-September-2021 at 8:24AM |
So I put my vacuum gage on it last night. It was a cold start so the choke was idling high as normal. The gage was reading a steady 20. When I kicked it down off the fast idle the needle jumped around from 12-18. Plenty of vacuum for the booster.
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JT, USAF Ret./Architect 1971 Ford F100 "Lizzy" 1971 Cougar XR7 "Kitty" 1984 Chevy Silverado "Sylvia" 2009 Smart Fortwo Cabrio "Lil Dude" 2015 Volvo XC60 R-Design "Sven"
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kychevyguy
Senior Member
Joined: 16-December-2013
Location: Lexington KY
Status: Offline
Points: 1996
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Posted: 02-September-2021 at 3:11PM |
Bled the brakes yet AGAIN. Some air was still coming from the back bleeders. I have some brakes, but the pedal has to go pretty far to engage the brakes. The pedal returns s-l-o-w-l-y (about 2 secs)
Progress!
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JT, USAF Ret./Architect 1971 Ford F100 "Lizzy" 1971 Cougar XR7 "Kitty" 1984 Chevy Silverado "Sylvia" 2009 Smart Fortwo Cabrio "Lil Dude" 2015 Volvo XC60 R-Design "Sven"
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kychevyguy
Senior Member
Joined: 16-December-2013
Location: Lexington KY
Status: Offline
Points: 1996
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Posted: 13-September-2021 at 12:53PM |
Progress! I removed the master cylinder and extended the rod that sticks out of the brake booster. The pedal no longer goes to the floor to stop the car. The pedal still return back slowly, but it does return. At least I no longer have to use my left foot to pull up the brake pedal. I need to drive it around the neighborhood to test the brakes, before I take it out into town on the real streets.
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JT, USAF Ret./Architect 1971 Ford F100 "Lizzy" 1971 Cougar XR7 "Kitty" 1984 Chevy Silverado "Sylvia" 2009 Smart Fortwo Cabrio "Lil Dude" 2015 Volvo XC60 R-Design "Sven"
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Compton
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Joined: 22-April-2017
Location: Auckland
Status: Offline
Points: 627
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Posted: 13-September-2021 at 1:24PM |
Nice one mateā¦gotta admire your perseverance
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handsofstone
Senior Member
Joined: 13-April-2018
Location: Northeast
Status: Offline
Points: 3941
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Posted: 13-September-2021 at 2:24PM |
That rod you adjusted has to be a specific length. My concern would be burning up the brakes. Like driving with your foot on the pedal. Is there a return spring for the pedal? I forget. You are gonna find out quickly if they are hanging up.
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californiajohnny
Moderator Group
Joined: 05-October-2013
Location: winlock, wa
Status: Offline
Points: 14606
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Posted: 13-September-2021 at 5:22PM |
it can if you go too far! jack up a front tire see it it turns easy by hand , hit the brakes hard and let off them see if it turns freely??? if not shorten the adjuster half turn at a time until it does
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JOHN 74 GRAN TORINO S&H CLONE 74 VETTE CUSTOM 90 S10 BLAZER 4X4 LIFTED 77 CELICA CUSTOM 75 V8 MONZA SUPERCHARGED 79 COURIER VERT. SLAMMED 75 VEGA V6 5 SPD 70 CHEV C10 P/U 68 MUSTANG FB CONVERSION
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pete rad
Senior Member
Joined: 29-November-2014
Location: usa
Status: Offline
Points: 305
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Posted: 14-September-2021 at 3:09AM |
handsofstone wrote:
Is there a return spring for the pedal? |
I do not know of any return spring being there. The only type of spring that is there is located inside of the brake light switch.
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pete rad
Senior Member
Joined: 29-November-2014
Location: usa
Status: Offline
Points: 305
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Posted: 14-September-2021 at 3:12AM |
Even on cars with manual brakes (non-power) the two springs that are located inside of the brake master cylinder, and the rear brake drum return springs all have to fully release when you release the brake pedal to keep the brake pedal in the up position.
And all of the brake calipers, brake pads and brake shoes have to fully release when you release the brake pedal.
There are also several return springs that are located throughout the parking brake system, such as the parking brake pedal and the parking brake cables to the rear drum brakes.
Edited by pete rad - 14-September-2021 at 4:02AM
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kychevyguy
Senior Member
Joined: 16-December-2013
Location: Lexington KY
Status: Offline
Points: 1996
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Posted: 14-September-2021 at 11:10AM |
As far as I know, the tiny spring inside the brake light switch only helps to turn off the brake light after releasing the brake pedal. The main brake pedal return spring is inside the brake booster. When I extended the adjustment on the master cylinder rod, I actually adjusted it quite a bit! I adjusted it out numerous full turns, probably about 3/16" total! The wheels still roll freely. The brake pedal does not start to grab until it is pushed about 60% down. BTW, I have zero parking brake, I have yet to tackle that issue. It is on the list though....
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JT, USAF Ret./Architect 1971 Ford F100 "Lizzy" 1971 Cougar XR7 "Kitty" 1984 Chevy Silverado "Sylvia" 2009 Smart Fortwo Cabrio "Lil Dude" 2015 Volvo XC60 R-Design "Sven"
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californiajohnny
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Joined: 05-October-2013
Location: winlock, wa
Status: Offline
Points: 14606
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Posted: 14-September-2021 at 3:10PM |
yeah check under there if the cable is all good and working the rear brakes could be way out of adjustment??? that could affect the pedal some...
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JOHN 74 GRAN TORINO S&H CLONE 74 VETTE CUSTOM 90 S10 BLAZER 4X4 LIFTED 77 CELICA CUSTOM 75 V8 MONZA SUPERCHARGED 79 COURIER VERT. SLAMMED 75 VEGA V6 5 SPD 70 CHEV C10 P/U 68 MUSTANG FB CONVERSION
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patchel73
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Joined: 26-October-2021
Location: Warrenton, VA
Status: Offline
Points: 3
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Posted: 13-April-2022 at 12:01AM |
This is great information, I was wondering what the difference between the later booster is. I wonder if you can re drill the hole to use retro fit? Thanks for the info about the rebuild shop. I see their price is much better than the last price I got. I just need it to work, not be ready for a show :-)
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Gran Torinos ROCK
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