Only time I had a similar problem was way back when the van was practically
new (400,000 miles ago).  I didn't bother gearing down for a long unpaved
downgrade.  We finally figured that the fluid was boiling, so compressible.
Hasn't happened since.

Karl Wolz

|-----Original Message-----
|From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
|BenT Syncro
|Sent: Tuesday, August 17, 2010 12:32 PM
|To: vanagon@GERRY.VANAGON.COM
|Subject: Re: brake question
|
|Hello Ms. Rogers,
|
|You may have been experiencing brake fade. It's not uncommon after using
|the brakes for an extended period over mountain grades. The rear brake
|drums may have warmed up enough to the point that the drum becomes bell-
|shaped and starts to lose contact except at the outer edges. Good argument
|for rear disc brakes.
|
|No disrespect to your mechanic but did he REALLY drive the vehicle for 30
|minutes and use the brakes? Dis he charge you for that time?
|
|An air bubble in the system could also exhibit such a symptom.  Or even a
|leak. I assume you're not finding any of the above. These sort of problems
|don't usually resolve themselves except for maybe air in the system.
|
|Don't change the master cylinder just on suspicion that it's bad unless you
|have the spare cash. It's a rather expensive guess.
|
|Glad to know your baby is able to take you around now. Not so happy that
|she's occasionally not able to stop her enthusiasm.
|
|
|Regards,
|
|BenT
|
|
|On Aug 17, 2010, at 12:04 PM, Sheilah Rogers <sheilah@SHEILAH.ORG> wrote:
|
|> 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.