[T3] Brake fluid change interval

[Jim Adney]

On 15 May 2016 at 19:54, Phil Hof wrote:

> I don´t remember seeing anything in the Bentley about changing the fluid, but there was a small insert included in my ´71 Owners manual.  It looked like a late addition, a sticker glued to the first page.  It said they recommended changing it every 18,000 miles or every year!
> 
> http://www.thesamba.com/vw/archives/manuals/aug70type3/titlewithcorrection.jpg
> 
> I always wondered what made that so urgent... maybe a failure pattern they sought to nip in the bid?

I've seen the same Owner's Manual addendum. The reason for changing 
the fluid is that standard polyglycol DoT 3 or 4 brake fluid is 
hydroscopic. That is, it absorbs water out of the air. Just sitting 
in your car, it gets more and more water in it as time goes by, and 
as the moisture content goes up, the boiling point goes down. 
Eventually, with hard brake use, the fluid boils and you suddenly 
have a system filled with a compressible fluid, which renders the 
brakes inoperative.  

If you live in a place that's not particularly humid, you're probably 
thinking that this doesn't apply to you, but it does. It certainly 
takes longer for the contamination to occur in arid climates, but it 
still happens.

Even if the fluid doesn't boil, damp brake fluid promotes corrosion 
of the interior brake system components. If you're looking for long 
brake service life, you don't want rust in there.

One of the big advantages of DoT-5 brake fluid is that it is NOT 
hydroscopic. That's what's in all my Type 3s, and has been since 
1977.

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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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