Date: Wed, 29 Jun 2016 20:27:15 -0400
Reply-To: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Subject: Re: Sticky brakes
In-Reply-To: <CALsWj8my06YpLfmoWtBhns32eHy+FH22Bsx6Uf5cWTjOoQ1=iA@mail.gmail.com>
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Brake fluid (glycol) is used as it gets along well with certain rubber/plastic parts. Yes it can absorb moisture especially since most of the system is exposed to ambient temperature changes and it not heated except at the calipers or pistons to drive the moisture out. Worse is that our vans have open caps to let air in as the fluid expands and contracts. Year ago many vehicles had a master cylinder with a cover and bladder over the fluid. As the fluid level went down the bladder would pull down with so fresh air never entered those systems.
In reality bakes should be inspected at some regular basis, at least once year or after any unusual situation such as an emergency stops or long term storage. At that point it is not a big deal to flush through some of the fluid. Same for power steering fluid. Some of that darkness could be from the rubber hoses or just from the moisture making the fluid cloudy. Changing it every two or three years will make most issues go away. Still, even with fresh fluid overheating the brakes to the point that the fluid gets to the vapor point will cause a low pedal next application. At that point there can also be caliper or cylinder damage so simply bleeding the brakes may not be sufficient.
Dennis
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of C. Abney
Sent: Wednesday, June 29, 2016 7:21 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Sticky brakes
The properties of brake fluid make it a frequent topic of discussion, and you know it makes me wonder just how much or little thought has been put into its continued use.
Brake fluid absorbs water from the environment. This water then causes corrosion in the system, brake fade when the brakes get hot, it might increase dissolved gases in the fluid.
I've never seen old brake fluid bled out that wasn't filthy. Where's that from?
What is it about brake fluid that makes it indispensable to a braking system? Isn't just about a certain level of viscosity? If that's so can't something better be substituted for it?
That said, there is a wide variation in the wet/dry boiling points of brake fluid. Even within one DOT rating. The vanagon uses dot 4, but dot 5.1 can also be used and is compatible with dot 4, and has a wet boiling pt. MINIMUM of 180C.
For some reason the high boiling point stuff, even though it's the same chemistry as dot 4 in general, is much more expensive. You're better off being diligent about changing your brake fluid regularly.
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