OK, strange situation.  My '85 Brat sat for a few months.  When I finally got into it again the brake pedal went straight to the floor.  No signs of leakage anywhere from brake lines, caliper or wheel cylinders.  No wetness on the inside of the wheels, no puddles on the ground anywhere. When I rev the engine pretty high I have a firm/normal brake pedal. When I let it return to idle the brake pedal goes stright to the floor.  When I hit the brake pedal at idle the engine stumbles and wants to stall.  Otherwise when driving around a nerby parking lot or idling the engine performs as it should.....until I hit the brake pedal then it wants to stall.  I've replaced the master cylinder with a new one.....same result.  I then replaced the hose and check valve from the intake port to the booster.....no change.  I bled all 4 corners.....no change in symptoms.  Am I looking at a bad power booster canister that may be malfunctioning internally?  Could the new master cylinder I installed also be bad right out of the box? This one has me stumped.  Given that the motor runs and idles fine I'm kind of ruling out vacuum leaks at the manifold.  There are only a fixed number of things it could be so I'm just trying to see what the concensus says before I attack it again. I need to add that all of the emissions stuff is long gone from this Brat and I'm running a 32/36 DGEV Weber. This thing ran perfect before I parked it for the summer. Any suggestions would be appreciated.

You shouldn't completely lose your brakes even if the power booster goes out. The travel of the pedal might change but you should still be able to hit the brakes and stop the car. That being said though the sighns are pointing twords a bad power booster

Edited November 26, 201411 yr by mikaleda

Nope, no braking at all using the pedal without getting the engine revs up over 3,000 RPM or so.  Booster vacuum leaking down internally? Maybe bad rubber brake hoses?

Edited November 26, 201411 yr by ettev

Mike , got your PM

 

Geez , been a long while....

 

Vacuum hose from booster to intake?

Probably unrelated but check that the plastic air suction thing isn't disintegrating. Just something I thought of in relation to my old gen 2 brat. Mine broke up and chunks of the plastic cause major carb/drivability issues when good old Skip took it home to PA.

 

Good luck ! Happy Thanksgiving!

I would say from your description that the vacuum canister is shot.

 

One should have 4 - 5 assisted brake applications on a power brake system with the engine not running. Varies by make/model...

But one will still have brakes after depleting the stored vacuum, it just takes a bit more leg input.

Point of brake actuating rod attachment is closer to the pivot point of the pedal on power brakes than it is non power brakes.

 

The fact that the vac canister doesn't hold vac, and that the engine wants to stall if brakes are applied at idle, surely points to bad canister.