I have an intermittent problem with braking on my '91 350SDL. Very hard
peddle usually on second application after start up, and then usually only
after brake application from reverse. This first appeared after the last
major service... lasted about two weeks then went away. Just started again
day before yesterday ( 6 weeks since major ). Has not occurred more than one
time in each run cycle, and as I said is intermittent even then. Did it
twice yesterday ( 1st in AM, 2nd at lunch...but not at days end ) and did
not do it this AM. I found with the previous incidence that if I did not
apply brake to stop rear motion ( backing out of driveway ) first, the hard
peddle did not happen. Vehicle will stop, but its scary to think it may
happen in a panic-stop situation, as it requires a great deal of leg
strength to apply peddle when this happens.

What do you think? Air bubble? Cylinder failing? I'd like your opinion
before it heads to the shop.