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pete rad View Drop Down
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Direct Link To This Post 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 View Drop Down
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Direct Link To This Post 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 View Drop Down
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Direct Link To This Post Posted: 28-August-2021 at 8:31AM
Originally posted by pete rad 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.


The brake pedal will return back up IF the engine is off though....
JT, USAF Ret./Architect
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kychevyguy View Drop Down
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Direct Link To This Post Posted: 28-August-2021 at 9:14AM
I am currently searching YouTube for ways to verify if the booster is good...
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 View Drop Down
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Direct Link To This Post 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
JT, USAF Ret./Architect
1971 Ford F100 "Lizzy"
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1984 Chevy Silverado "Sylvia"
2009 Smart Fortwo Cabrio "Lil Dude"
2015 Volvo XC60 R-Design "Sven"
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72 RS 351 View Drop Down
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Direct Link To This Post 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.
Don
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handsofstone View Drop Down
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Direct Link To This Post 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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Direct Link To This Post Posted: 30-August-2021 at 11:03AM
Originally posted by 72 RS 351 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.
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.
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 View Drop Down
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Direct Link To This Post Posted: 30-August-2021 at 11:04AM
Originally posted by handsofstone 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.
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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Direct Link To This Post Posted: 30-August-2021 at 11:12AM
Check that tree for damage or leaky hoses leading elsewhere.
"What we do in full frontal view, is more honest than your cleaned-up mind."
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handsofstone View Drop Down
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Direct Link To This Post 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 View Drop Down
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Direct Link To This Post Posted: 30-August-2021 at 4:38PM
Originally posted by handsofstone handsofstone wrote:

  How much vacuum does your engine produce? Curious.

Is this something that originally just happened overnight?



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.
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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Direct Link To This Post Posted: 30-August-2021 at 9:39PM
not lbs... actually in. of Hg ( inches of mercury)Wink 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...
JOHN
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handsofstone View Drop Down
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Direct Link To This Post 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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Direct Link To This Post 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.
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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Direct Link To This Post 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!
JT, USAF Ret./Architect
1971 Ford F100 "Lizzy"
1971 Cougar XR7 "Kitty"
1984 Chevy Silverado "Sylvia"
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Direct Link To This Post 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.
JT, USAF Ret./Architect
1971 Ford F100 "Lizzy"
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1984 Chevy Silverado "Sylvia"
2009 Smart Fortwo Cabrio "Lil Dude"
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Direct Link To This Post Posted: 13-September-2021 at 1:24PM
Nice one mateā€¦gotta admire your perseverance
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Direct Link To This Post 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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Direct Link To This Post 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 doesWink
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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 View Drop Down
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Direct Link To This Post Posted: 14-September-2021 at 3:09AM
Originally posted by handsofstone 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 View Drop Down
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Direct Link To This Post 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 View Drop Down
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Direct Link To This Post 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....
JT, USAF Ret./Architect
1971 Ford F100 "Lizzy"
1971 Cougar XR7 "Kitty"
1984 Chevy Silverado "Sylvia"
2009 Smart Fortwo Cabrio "Lil Dude"
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Direct Link To This Post 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...
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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Direct Link To This Post 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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