master cylinder vacum leak
 

Need some help...
I have a 1965 El Camino 327 SB
Power drums front and rear
I hear a vacum leak at the bottom of the master cylinder seems to be a hole there
sucking in air...is this normal...
engine runs fine idles fine....what do you guys think???????

how much air does it leak ? and thru what sort of hole ?

if its a factory intended leak, i would expect it to be thru a simple round hole in the case

power brakes are supposed to retain some vacuum if the engine dies - its a "save-your-ash-from-dieing" feature so that if the engine cuts out, you can bring the car to a safe stop

find a good size parking lot, or even an empty street at night and try simply shutting off your engine as you drive 40, wait about 2 seconds between hitting the switch and hitting the brakes, you should still have the power to safely stop the car.

if you car fails this test, plug the hole, try again, see if it changes

You may have a bad booster. There is a seal between the master cylinder and booster that is supposed to not allow fluid suction if there is a leak in the booster. It may be that the booster has a small leak but is not sucking the fluid out of the master cylinder.

Might want to slide the master cylinder forward and see if you hear the leak from around the booster pushrod seal.

No vacuum hoses cracked/leaking around that area is there?

Sounds like you have a bad booster (ruptured diaphragm).
If the master cylinder leaks it will fill the booster up to the rod then leak out around it. otherwise there is no liquid transfer between the master cylinder and the booster. You can get a new diaphragm and install it your self.

Troy

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69 SS/RS full custom Camaro 98 ISCA Grand Champion
69 SS/RS BB Camaro wifes driver
66 Elcamino 350/all dz parts,ac,windows,loaded,my driver
69 SS Chevelle BB conv.fresh frame off
26 T sedan street rod

Thanks all for all your help.....Turned out to be a bad power brake booster.