Any ideas why my brake pedal goes to the floor?

[SEdgell]

1986 325es

As the title states, the brake pedal goes straight to the floor when first pressed. After the pedal goes to the floor I can pump it 2 or 3 times and it will build pressure, but after you release the pedal for about 30 seconds or so it goes to the floor again. I'm not sure if this could be a vacuum issue or not, as I'm pretty sure that I have a vacuum leak somewhere which causes the idle to sometimes surge. There is plenty of fluid in the reservoir and I haven't found any leaks. I don't know if this will help or not but it does this with the the engine on or not. Any suggestions?

[5Toes]

Well using common sense.. I am far from an expert...

I believe it cant be a vacuum issue, because withe car off it cant be a vacuum problem

[Sagaris]

fluid is leaking past some sort of seal

Most likely the master cylinder or one of the calipers is bad.

[E30_fiend]

have you done any brake work recently? My first thought would be air in the lines. If you havent done any recent work, I would say your master is taking a shit. You can find good used ones all day long for cheap.


Taylor

[carfantiti]

check fluid lvl
rear brakes are drum right than check rear wheel cylinder 's take a screw driver and look under rubber boot to see if leaking .
check bleeder screw front and back brakes
check all brake lines
check front calipers for brake fluid
check around master cylinder for brake fluid might need to get under car and look up with flashlight .
once you determined there is no brake fluid leaks .
than change brake master cylinder.
if you found any leaks than change what is leaking first.
If you did any recent brake work than power bleed the brakes first.
it will be one those problems I mentioned.Don't think about booster that would give you a hard stiff pedal not soft.
best of luck.

[jlevie]

This sounds most like a leak in the system or a bad master cylinder. If you can't find any leaks, replace the master cylinder. And when you replace the master cylinder check to see if there is brake fluid in the booster. If there is, also replace the booster. Brake fluid will kill a booster pretty quickly.

[BimmerTim]

100% master cylinder.

[SEdgell]

Thanks for the responses. I haven't done any brake work to it lately...I haven't even driven it since probably March or April. I'll do a good leak search, I've checked the fluid level, and checked the garage floor and didn't find any leaks. It has rear disc btw.