first question is,
when the brake pedal went nearly to the floor, did you pump the brakes some
?

it's the natural thing when the pedal goes down too far, to take another
stroke on the pedal...
if the brakes pump up like that ..
makes you think about the master cylinder.

vacuum brake booster problems are harder to diagnose, and pretty rare, but
always need to be considered.

at least bleed the brakes and see how that goes.
Bleeding a hydrocyanic system is not only a service that should be done
every now and then ( two years ) it's also a diagnostic operation.
Might learn something about how well the master cylinder works during the
bleeding process, which is why, btw ..I like a pump-the-pedal method of
bleeding ..you can feel and see what is going on with the MC that way.
I'd start there.
Scott
www.turbovans.com
----- Original Message -----
From: "Sheilah Rogers" <sheilah@SHEILAH.ORG>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Tuesday, August 17, 2010 12:04 PM
Subject: brake question

Howdy Folks,

I'm wondering if I can bother the list's hive mind for some answers (that I
already could not find via the search tool)?

Basically something went weird with my brakes and my mechanic cannot
reproduce the problem.

So I was driving in ~80F weather, up and down a not so steep road but some
curves, about 30 minutes of said road was unpaved, van warmed up of course.
Brakes no problem. (not sure if weather matters but there it is.) I drove
about 45minutes total here.

Then I got on the highway for another 45 minutes-ish. When I went to slow
down a bit, it was like my brake peddle wasn't responding with its normal
sort of push-back and instead, the brake pedal just dropped with no brake
functionality about 80% to the floor before it engaged. Once engaged, I
could slow the van down but of course I then had the pedal to the medal just
to slow down a bit.

Being on a quiet highway I kept going, figured I'd pull over in a bigger
town and at least I can stop the van. But after 30minutes, the brake resumed
normal so I just continued driving to my mechanic's.

The next day he could not reproduce the problem, after warming up the van,
driving on hills, 30minutes or so. He says 50% chance it's the master
cylinder. But he's not sure (???) what else it would be since the brake
fluid seems fine.

Anything else that should be ruled out or should I just have the master
cylinder replaced and hope it doesn't give out (50% chance?!) the next time
I'm driving on presumably worse mountain roads. I don't feel safe or
comfortable with this plan.

Does anyone want to weigh in at all?
Mucho thanks appreciated.

Sheilah

1986 Westy water-cooled vanagon: Vanna White.