I just bought a Jetta for $650 today and drove it back home a half hour with a slightly blown head gasket and a leaking pump. I test drove it, brakes worked perfect. Paid the money got the title, then... while pulling out of the seller's driveway the driver side cv joint at the transmission fell off! We jacked it up and bolted the 6mm allens back down tight. Before this the brakes worked fine, immediately after the brakes sink to the floor. I couldn't find a leak but it was getting dark, could the cv have fallen on the line and cracked it? A leak in the vacuum because of the pump leaking wouldnt cause the pedal to drop, would it? Or simultaneously the master cylinder failing? I decided to drive it home slowly and downshift because the brakes had only %20 power i'd say. What would be the first thing you'd check?
I'd look to see if you crushed or otherwise damaged the brake lines by placement of the jack when you lifted the car to work on the axle.
I would also look at the rubber brake line on that front wheel.
It might be possible the master cylinder just went junk esp. if this car has been sitting undriven for some time. Also, one of the rear wheel cylinders may have let go (this is common if old).
I can't help to think this car is going to be filled with problems if the moron who sold it to you couldn't even get the axle back on properly. Sounds like the owner encountered problems he was not interested in dealing with. Good luck and deep pockets.
Additionally, the Jettas utilize a rear brake actuator valve. It is located ahead of the driver's rear tire on the Mk. II's.....I have not owned a Mk. I for a long (happy) time, so I am unsure where it is located. Probably in the same spot.
Over time, these valves begin to leak and will allow the pedal to go very slowly to the floor. It is often VERY difficult to see a leak on one of these. You can park it and put a very dry, clean piece of cardboard under the car back there and it will usually drip. The first hint that it is one of these malfunctioned is that you can bleed the brakes and all is well...and then, suddenly all is not well.
We jacked it up and bolted the 6mm allens back down tight. Before this the brakes worked fine, immediately after the brakes sink to the floor. I couldn't find a leak but it was getting dark, could the cv have fallen on the line and cracked it? A leak in the vacuum because of the pump leaking wouldnt cause the pedal to drop, would it? Or simultaneously the master cylinder failing? I decided to drive it home slowly and downshift because the brakes had only %20 power i'd say. What would be the first thing you'd check?