Date: Thu, 19 Aug 2010 13:25:46 -0700
Reply-To: Scott Daniel - Turbovans <scottdaniel@TURBOVANS.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Scott Daniel - Turbovans <scottdaniel@TURBOVANS.COM>
Subject: Re: brake question
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
reply-type=original
I think you're on the right track with putting in a new master cylinder.
( you can have internal leaking between the two portions or sections of the
dual tandem master cylinder chambers ...........no air is involved....just
pressure does not get distributed like it should. Perhaps that's what's
going on with yours. If the MC is say, 10 years old or older, not a waste
of $ to put in a new one.)
Dot 4 brake fluid is what is supposed to be used on Vanagons.
If someone puts in Dot 3 it's not the end of the world , but Dot 4 is
better, has a higher boiling point, and is what's called for on vanagons. )
re fad ..
I don't think you actually had brake fad. 30 minutes of not using brakes..
( provided the system is working like it should ) is plenty long enough to
cool things down.
I suppose a stuck piston in a caliper could keep a front brake partially on
....contributing to fade happening. Make sure the front wheels turn easily
when brakes are not applied.
Forget what year vanagon you have, but on the 80 to 85 dual piston calipers
..
its' common for one piston to get semi-stuck , often the right side outer
piston. So make sure that's working fairly right.
About braking on descents ..
Don't use continuous light or medium braking. Instead, use them a bit more
than you need to, bleed off some speed, then let speed pick back up not
using the brakes, then brake again ..brake, cool, brake, cool, etc. Not
continuous light or medium braking .
in general on brake use -
use them a bit harder than needed now and then intentionally.
Constant only light use contributes toward making brake squeal happen in
disc brakes.
Use 'em like to 70 % of their ability every now and then , like once a week
say, intentionally.
Not a panic stop or anything like that ..just a little harder than needed
now and then.
there is also a test for the vacuum brake boosters function ..
'usually' vacuum brake boosters last really, really well on vangons.
Scott
www.turbovans.com
----- Original Message -----
From: "Sheilah Rogers" <sheilah@SHEILAH.ORG>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Thursday, August 19, 2010 7:23 AM
Subject: Re: brake question
Thanks everyone for all the info - so helpful! :)
So here's what I did:
Ruled out brake fade since I imagine that by the time this happened, the
brakes would have had plenty of time to cool down (~45min on mostly empty
highway).
There was no fluid loss when the mechanic checked.
The mechanic ruled out air in the system stating that if that were the case,
I should have been able to reproduce the problem more readily since it's a
closed system and the air would have still been there.
And the brakes working-failing-working did seem to suggest that master
cylinder....
(Unfortunately I did forget to ask him to bleed first for diagnostic
reasons).
But instead, I asked the mechanic to go ahead and replace the master
cylinder (he says that's 2hours labor, fwiw, and hopefully you all agree
that's more or less correct). He added that replacing the cylinder would
inherently mean new fluid, therefore bleeding out, and fixing any potential
air bubble issues too.
I forgot to ask him (and youse) if anyone's using the new .4 over .3 brake
fluid.... so I'm not sure what he put in. I just know that a friend who
drives a (school) bus is using the newer .4 and recommended that (but he
doesn't know VW).
You all have made me think about pumping up the brakes. I've never thought
anything of it. Certainly on downgrades I will (to prevent that brake
fade)... Without knowing to do that, I'm pretty sure that I naturally would
have tried to pump a few times, if for no other reason, hoping they'd engage
in some way that the prior attempts hadn't caught. As for the brakes
resuming their function, it did NOT happen immediately after pumping, more
like 30minutes later.
I suppose it's possible that brakes take more time than 30min to cool down
(suggesting that it was brake fade and not the master cylinder...) Along
similar lines, I suppose pumping the brake maybe returns functionality more
quickly than the less pumping (and subsequent more time) to return
functionality that I experienced (thereby suggesting that it was again, NOT
the master cylinder). IF this is all true, than I might have replaced that
sucka for nothing except a great lesson in brake fade, bleeding, and a brand
new part. Hmph, we'll see, eh.
Well, again, I hope I made the right decision, certainly couldn't make it
without all your inputs. THANKS again!
These vans sure like to be touched a lot...
Sheilah
>
>
> ________________________________
> From: Sheilah Rogers <sheilah@SHEILAH.ORG>
> To: vanagon@GERRY.VANAGON.COM
> Sent: Tue, August 17, 2010 3:04:44 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.
____________________________
Sheilah Rogers, L.Ac.
http://sheilah.org
tel: 415/ 730-4144
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