No power brakes
#1
Hi everyone. 
I need some major help.  Huh Huh
I can not seem to get the power brake to work. I might as well cut a hole in floor pan and use the Fred Flintstone method of stopping. Lol
I’ve disconnected the manifold vacuum and installed a external vacuum pump feeding directly to the new master cylinder and new brake booster to no avail.  Lines have all been bled extensively. 

I can put my full weight on the brake peddle and it will barely but slowly stop the car. It feels like the brakes are trying to engage, but just don’t have the pressure to do the job. 
 Is it possible that it’s a problem in the drumbs or disk brakes. 

Would appreciate any advice you can give.
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#2
What are you working on, 1969, 1970, etc. and is it a factory power brake car or did you or a previous owner convert it to power brakes?

My initial guess is your new booster is bad.  It's always best to have your old OEM booster rebuilt or buy a rebuilt OEM booster from places like West Coast Classic Cougars.  Parts store boosters are often garbage.  And that repro booster that Scott Drake offers is merely a cheap China universal import with a mounting plate attached to it.
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#3
(06-12-2019, 09:23 AM)1969_Mach1 Wrote: What are you working on, 1969, 1970, etc. and is it a factory power brake car or did you or a previous owner convert it to power brakes?

My initial guess is your new booster is bad.  It's always best to have your old OEM booster rebuilt or buy a rebuilt OEM booster from places like West Coast Classic Cougars.  Parts store boosters are often garbage.  And that repro booster that Scott Drake offers is merely a cheap China universal import with a mounting plate attached to it.

71 Mach1  Came with factory power booster front disc rear drum. So far even my mechanic can’t figure it out. That’s why I’m asking.
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#4
How strong is the vacuum signal to the booster, if it's less than about 14" the power assist starts to suffer.  12" of vacuum to the booster is really the minimum for any type of power assist.  If the vacuum signal is okay, I'd think you have a bad booster.  Where did your mechanic get the new booster?

Just to clarify, the brakes will work, just the pedal force needs to be extremely high?  Asking, because if the won't work at all regardless of how much you push on the pedal, there is a chance something hydraulic is plugged somewhere.  But, if something is plugged, you should still feel some power assist.

One test I have heard of is with the engine off press the pedal several times to eliminate any residual vacuum inside the booster.  Then, while very lightly touching the brake pedal start the engine.  If the booster is working you should feel the brake pedal pull down a little bit.
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#5
(06-13-2019, 02:41 AM)1969_Mach1 Wrote: How strong is the vacuum signal to the booster, if it's less than about 14" the power assist starts to suffer.  12" of vacuum to the booster is really the minimum for any type of power assist.  If the vacuum signal is okay, I'd think you have a bad booster.  Where did your mechanic get the new booster?

Just to clarify, the brakes will work, just the pedal force needs to be extremely high?  Asking, because if the won't work at all regardless of how much you push on the pedal, there is a chance something hydraulic is plugged somewhere.  But, if something is plugged, you should still feel some power assist.

One test I have heard of is with the engine off press the pedal several times to eliminate any residual vacuum inside the booster.  Then, while very lightly touching the brake pedal start the engine.  If the booster is working you should feel the brake pedal pull down a little bit.

Thanks. I will double check the vacuum pressure but I think it’s going. I’ll also try that test. As far as the brakes working! They barely do. Put my full weight on the peddle as far as it goes down. I can feel the brake making contact with pads but it like there not applying any pressure to the pads. Feels like they are just touching or rubbing against them.  Does this do much good.
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#6
(06-13-2019, 01:09 PM)Dave Allred Wrote:
(06-13-2019, 02:41 AM)1969_Mach1 Wrote: How strong is the vacuum signal to the booster, if it's less than about 14" the power assist starts to suffer.  12" of vacuum to the booster is really the minimum for any type of power assist.  If the vacuum signal is okay, I'd think you have a bad booster.  Where did your mechanic get the new booster?

Just to clarify, the brakes will work, just the pedal force needs to be extremely high?  Asking, because if the won't work at all regardless of how much you push on the pedal, there is a chance something hydraulic is plugged somewhere.  But, if something is plugged, you should still feel some power assist.

One test I have heard of is with the engine off press the pedal several times to eliminate any residual vacuum inside the booster.  Then, while very lightly touching the brake pedal start the engine.  If the booster is working you should feel the brake pedal pull down a little bit.

Thanks. I will double check the vacuum pressure but I think it’s going. I’ll also try that test. As far as the brakes working! They barely do. Put my full weight on the peddle as far as it goes down. I can feel the brake making contact with pads but it like there not applying any pressure to the pads. Feels like they are just touching or rubbing against them.  Does this do much good.

With the car on jackstands have you tried having one person manually rotate a tire and another apply the brakes?  Just trying to determine if something is plugged, but, since you mentioned in your first post they were bled extensively it's starting to look there is no power assist.


Is the pedal going nearly to the floor?  First, if there is no air in the system and the master cylinder is leaking internally the pedal with go nearly to the floor and the brakes will not work.  Second, rear brakes far out of adjustment will cause the pedal to travel too far and the brakes will work but not as well as they should.
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