[T3] Master Cylinder Sleeving

Jim Adney jadney at vwtype3.org
Sat Oct 1 17:02:47 PDT 2022

On 1 Oct 2022 at 14:47, Max Welton wrote:

> I would recommend flushing DOT-5 every few years too. Water still gets
> into the system but pools somewhere as it doesn't go into suspension with
> silicone based DOT-5.

I've never seen that to be a problem, and I've been doing this for decades. I 
suppose it might happen if you take your car swimming, but otherwise....  ;-)

Certainly water gets in as a vapor, but I've seen no evidence that it coaleses 
into liquid form. There's no reason for that to happen. I've even done 
experiments with a test tube full of DoT-5 with a drop of water in the bottom. 
Let it sit around for a few months and the water drop is gone. The water 
slowly turns to vapor and migrates out.

My later Type 3s, which have the dual bleed valve calipers are good test 
beds for this. After converting to DoT-5, I drive them for a few weeks, then 
drain a bit off the bottom to see what else has settled there. The old DoT-3 
or 4 is heavier than DoT-5, so it tends to collect at the bottom, where it is 
easy to drain out, if there's any there.    

Typically, after a few weeks, I'll get maybe 1 cc of old brake fluid out of each 
caliper. After than, one, two, or 4 years later, almost nothing comes out other 
than DoT-5.

The two types of fluids are easy to tell apart: DoT-5 will be purple or clear, 
while DoT- 3 & 4, with or without water, will be rusty brown.

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

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