Power brakes aren't power

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SwingerSteve

SwingerSteve

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I did the front brake conversion on my 70 Swinger,, swapped the stock drums to power disk from a 73 Swinger,, swapped the proportioning valve and master cylinder and booster from it too,,, I have a slight "power brake" feel at first but have to push hard to stop the car,,, did I miss something or is the master possibly bad?
 
Most likely the diaphragm in the booster is shot.
Make sure you have sufficient vacuum going to the booster and that's about all you can do without replacing it.

The good clue you gave was that it seems to have boost at first.
This tells me the rubber diaphragm is split and when it starts to move that split opens loosing the vacuum.

Engine idle probably changes when you press the brakes also.
 
Is your engine stock? Does it have a non stock camshaft?
 
Are you sure you bled the brakes to ensure that you got all the air out of the system?? Do you have plenty of vacuum??

treblig
 
Treblig said:
Are you sure you bled the brakes to ensure that you got all the air out of the system?? Do you have plenty of vacuum??

treblig
Click to expand...
Bled them twice and fairly sure they're air free,,,, When I pull the vaccum hose off it kills the car. Plugged the nipple on the intake and feels like I have good suction.
 
TrailBeast said:
Most likely the diaphragm in the booster is shot.
Make sure you have sufficient vacuum going to the booster and that's about all you can do without replacing it.

The good clue you gave was that it seems to have boost at first.
This tells me the rubber diaphragm is split and when it starts to move that split opens loosing the vacuum.

Engine idle probably changes when you press the brakes also.
Click to expand...
 
I'll start by taking the booster off and see what it all looks like,then re bleed the system,,, thanks !!!
 
SwingerSteve said:
I'll start by taking the booster off and see what it all looks like,then re bleed the system,,, thanks !!!
Click to expand...

Bleeding has nothing to do with no power assist.
Maybe unplug the vacuum from the booster and see if it feels the same when braking.
This might give you a baseline feel weather it has boost or not.
If it feels and stops the same with the booster disconnected, def the booster is bad but you said the pedal is hard to push?

That's a bad booster.
 
Definitely sounds like a bad booster if you have enough engine vacuum. I have had boosters that held vacuum and still were bad. Last one I changed from manual to power 1. the pushrod was a different length and 2. the pedal assembly had the hole in a slightly different location. Different travel/leverage.
 
GeorgeH said:
Definitely sounds like a bad booster if you have enough engine vacuum. I have had boosters that held vacuum and still were bad. Last one I changed from manual to power 1. the pushrod was a different length and 2. the pedal assembly had the hole in a slightly different location. Different travel/leverage.
Click to expand...


And there's that. :D
To the OP, you should be able to stop the car with one or maybe two fingers on the pedal with a working booster.
 
SwingerSteve said:
Stock engine EXCEPT cam,, it's a mild cam.
Click to expand...

You say mild. Do you know the specs? How does the cam idle? Does it have a bump to it? It could be you have low manifold vacuum that the power brakes don't operate well.
 
One other thing is the one way check valve on the booster. The ninty degree nipple that the hose plugs onto.
 
Just throwing this out you sure the prop valve was a prop valve not a distribution block?
 
SwingerSteve said:
... Plugged the nipple on the intake and feels like I have good suction.
Click to expand...
A vacuum gage would be more quantitative than "feel". Useful for many diagnostics on your car. Can even use the little one on a Mighty-Mite hand pump, which is also almost essential in the garage. If you suspect the camshaft, run a hose over from the vacuum on another car that has a booster which works, while the other car is idling. Could be a 2017 car, boosters haven't changed.
 
I have always ran the vehicle then pried the check valve off and saw or hear if the vac is in the booster, cheap and easy without any tools.
 
I need to make mine a little squishier... with full vacuum, ebc brakes, and stainless hoses... i lock em up with just a little effort.
 
Does "EBC brakes" (pads) imply front disks? If so, most people don't find them too easy. If you still have rear drums, you need a proportioning valve for the rear circuit to reduce the pressure. Otherwise, the rears will skid before the fronts, which might be what you are experiencing. An adjustable p.v. is ~$30 on ebay. One member here instead installed much smaller rear wheel cylinders, which would also work if you can hit the target. With adjustable valve, tune it in a wet parking lot until the front skid just before the rears.
 
Run car for about 5-10min. Shut car off. Wait about a hour. Pull the hose off the brake booster. If you hear a woosh the diaphragm is holding vacuum. If you hear nothing the diaphragm is bad, unles you are expiriencing the partial split that trailbeast explained then it would be hard to detect this way. But this is the easiest and quickest test to do
 
Thanks guys,, appreciate the help. All the different opinions bring the steps into prospective instead of 1 mind whirling and thinking,, well it could be this that or the other,,, your experiences make a guy slow down and create diagnosing steps..
 
Engine off, pump the brakes about 5 times,push down on the pedal and keep it there,start car, pedal should fall about 1 inch. If it does the booster is working. release pedal.

Engine running, pump the pedal about 5 times, the engine should not care a bit and continue to happily idle.Diaphragm is good.

From under the hood engine idling. Clamp the booster hose with a large enough plier to completely cut off the vacuum to the booster. The engine idle should not change one bit. Pump the pedal about 5 times.Release the clamp;engine idle should falter and recover to normal. Booster diaphragm is good .
 
AJ/FormS said:
Engine off, pump the brakes about 5 times,push down on the pedal and keep it there,start car, pedal should fall about 1 inch. If it does the booster is working. release pedal.

Engine running, pump the pedal about 5 times, the engine should not care a bit and continue to happily idle.Diaphragm is good.

From under the hood engine idling. Clamp the booster hose with a large enough plier to completely cut off the vacuum to the booster. The engine idle should not change one bit. Pump the pedal about 5 times.Release the clamp;engine idle should falter and recover to normal. Booster diaphragm is good .
Click to expand...
Going to do those tests,, Thanks!!
 
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