Brake sponge & hiss (1 Viewer)

[77wagon]

I have just replaced all front brake wheel cylinders, pads, springs, etc... And when I was bleeding the brakes I noticed an "air" leak or something coming from the master cylinder/booster area. It sounds like a quick "pissst" and it corresponds with the pedal clunking and then dropping. Did the diaphragm in the booster just go out? The brakes work great when pumped. I have bleed them three times. There seems to be no air in the lines. Every time I pump the breaks it is spongy on the first pump. It only takes a few seconds to get spongy again.

I tried holding the brake while starting the vehicle and the pedal dropped a little, but not much.

As you may gather, I am a rookie and any advice will help. Thanks

 

[vangasman]

You still got air in the system. Had to "burp" the wheel cylinders last time I replaced them.

 

[77wagon]

How do you "burp" the cylinders?

 

[77wagon]

Also I am familiar with pumping the brakes when there is air in the system. But I have never experienced the air release and petal drop?

 

[bikersmurf]

Disconnect and plug the vacuum line to the booster. Does the his change?

I suspect a sick booster, master, and air in the system. I recently replaced my booster and master, and am surprised how well the brakes work now.

 

[77wagon]

I took off the vacuume hose and the pedal had smooth travel. It no longer "thumped," hissed, and then dropped. But as soon as I reattached the hose, it was back to the same thing. If I held my thumb over the vacuume, the pedal became hard and barely moved much. I assume it is the booster?

 

[bj40green]

..... There seems to be no air in the lines. Every time I pump the breaks it is spongy on the first pump.

Spongy = air in the line(s) which you compress by pumping until you feel that it is hard. After releasing the pedal the air expands and the system is spongy again.
Was there a moment that the fluid reservoir was empty? If so, you have to bench bleed the master cylinder or keep bleeding the system till that air bubble is out.

Rudi

 

[77wagon]

I'll try to keep bleeding it tomorrow. Thanks

 

[bikersmurf]

I took off the vacuume hose and the pedal had smooth travel. It no longer "thumped," hissed, and then dropped. But as soon as I reattached the hose, it was back to the same thing. If I held my thumb over the vacuume, the pedal became hard and barely moved much. I assume it is the booster?

Sounds like something is wrong with your booster. They don't hiss when working properly. A booster from a 4runner, mini truck, 40,55,60,70,80 will bolt in.

How old is your master?

In your op, you referred to cylinders and springs... Your drum brakes likely need adjustment. Pumping can also help with that problem.