Brake Failure

[dunkindeso]

Mk4 with 352k miles. Pulling out of the driveway at very low speed, service brake feels normal (good) suddenly hear an audible but quiet pop noise and brake pedal sinks to the floor with no resistance and all braking power lost. Parked it back in the driveway and pumped the pedal a few times still with zero resistance and suddenly pedal pressure and brake function returns. I continue pumping the pedal expecting a sizable amount of brake fluid leaking under the car. Zero sign of leak and the reservoir is full. What just happened?

 

[Seatman]

All I can think is maybe a bit of dirt hit the seals in the master cylinder so the fluid went by them. Either that or the seals are maybe bad.

 

[KrashDH]

Is your belly pan on? Could be you lost fluid but it's still hung up in the pan. If it were a vac issue, you'd get a hard pedal, so I agree with the above. Master cylinder potentially on it's way out...

 

[dunkindeso]

Thanks guys. No belly pan. I figured it had to be the master cylinder but found it interesting that there was absolutely zero brake considering redundancy inside the master.

 

[valvecrusher]

did you check this hose for a crack/split in ANY point between the ends?

It goes between vacuum pump, under the air intake tube from filter, back to the brake booster on firewall, drivers side...
look under the air intake tube(from intake -air filter- box)

The middle section is 90°, very thin plastic...and has caused numerous brake vacuum related failures...after some age gets accrued....

you might see a split in the center section at ANY point, bottom side, or where the tube slides over the bungs either on booster side, or the vacuum pump side...
DAMHIK,
but lots of folks had weak or spongey brakes, and changed masters/slaves, bled the brakes, changed boosters....
but it was that tube...

which is $12 for aftermarket shipped on the auction site....
your luck may vary...


Did you check this line with a mirror, your eyes, and fingers?
Just throwing it out there...hope you get it figured out!

vc

oh yeah, you can suspect this part if pumping the brakes with the Engine OFF, you have a firm pedal, but with engine running you have a soft, falling pedal....

 

[KLXD]

Yeahbut. He said the pedal went to the floor. Nothing about a failed booster would cause that.

 

[dunkindeso]

no issues with brake booster. i suppose this is more of a psa to anyone like me who thought outright failure of the braking system was impossible with redundancy in the master cylinder

 

[KLXD]

The thing is, the rears could fail and most people wouldn't know until the front failed too.

 

[KrashDH]

The thing is, the rears could fail and most people wouldn't know until the front failed too.

Happened to me. Went to go to work and the pedal wasn't right, lost pressure. 1st inspection was at the calipers. Passenger rear piston seal had failed. Had to have the car towed home since I was a long distance from home.

 

[Zak99b5]

The brake fluid could’ve leaked into the booster.

 

[dunkindeso]

Like i said master cylinder reservoir is full and braking action was normal (good) not indicative of any issue with the rear brakes. I sincerely hope people are able to notice brake failure on their back wheels i’m thinking of scrapping this car unless anyone in the MA area is looking for a beater. Thanks all for your time.

 

[KrashDH]

Scrapping a car because of a brake issue you don't want to track down? Dang if I was an east coaster I'd take it no prob.

Seems like an extreme solution

 

[dunkindeso]

Rebuilt title and spotty history. It’s a beater quality car which is great in its own regard but after my own 80k miles and most recent 5k miles being devastating in terms of random failure items i’ve decided brake failure is the final straw.

 

[befarrer]

I had a master seal randomly go out on a B2200, went from working normal to no pedal at all, no resistance all the way to the floor and no brakes within 3 brake applications. Master cylinder seals went, bypassing internally, I had no brake fluid loss at all.