I bought a 1986 560SL that had been sitting for several months. I took it out for some low speed driving and lost my brakes temporarily. The pedal went to the floor and I had to pump the pedal for brake pressure. I managed to get the car home and I've been testing it up and down my driveway. I can't get it to do it again. Could there be some valves in the master cylinder gone bad? Could it be caused by months of inaction? If so, whu did the pressure come back later? I'm afraid to drive it now. Could it bew the brake booster? How can I tell the difference?

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1991 560SEL (254K miles)
1980 Lincoln Mark VI - Givenchy
1979 Lincoln Mark V Collector's Series
1979 Lincoln Town Car Collector's Series
1979 Ford "Effie" Pickup (in gradual transformation to a show/street truck)
1969 Lincoln Mark III (waiting for "Overhaulin" to call)
1989 Lincoln Towncar
2001 Lexus GS300 (spousal unit's daily driver)

Could be the brake fluid. Flush it out, check the system for leaks.

Easiest way to see if you have a leak. Take care of it soon!

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J.H.
'86 300E