[T3] I want to change my brake fluid it's been a while? 73 SB

[Jim Adney]

On 13 May 2016 at 22:25, Dave Hall wrote:

> I've a simple piece of rubber pressure tubing that has a screw in the
> lower end, and a slit cut with a Stanley knife (eg) which fits on a
> bleed screw and acts as a one way valve.  Press on the pedal and the
> fluid squirts out of the slit, without allowing air back in.  Good for
> single-handed bleeding, but rather slow for changing fluid. 

It's a standard chem lab trick, except that instead of a screw, you 
use something inert, like a glass or ceramic bead that's slightly 
larger than the ID of the tubing. For brake fluid, a steel ball 
bearing would be a good choice.

Frankly, I considered doing this, but the plain tube in the bottle 
works perfectly well. Backwash on the upstroke is minimal, so nothing 
but fluid gets drawn back in if the upstroke is quick and the tube 
runs a bit uphill from the bleed valve. And even if you suck in a 
tiny bubble, gravity flow will bring it out a second or 2 later, so I 
often don't even bother with the uphill part.

Maybe the key is how you pump. Do it quickly, both up and 
downstrokes. If you watch the tube while someone else does this, 
you'll see the fluid move out into the tube 2-4 inches on each 
downstroke and back up maybe 1/4" on each upstroke. Fast pumps are 
also important for creating turbulence in the system, which helps 
stir up dirt & rust and carry it out of the system.

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