[T3] Master Cylinder workover

[Jim Adney]

On 19 Aug 2015 at 20:41, Keith Park wrote:

> my 71 still has the master I put in it in 1988 when I got it, still the DOT3
> or 4 as I didnt want to keep eating the brake light switches and havent
> converted yet. 

I'm not at all convinced that the DoT-5 has anything to do with 
failing brake light switches. The failed switches that I've cut apart 
have shown no sign of brake fluid having gotten past the seal that 
separates the fluid from the moving parts, where the failures occur. 
While it's possible that there were tiny amounts that got thru but 
were not visible, I remain skeptical. Most of the failures I've seen 
happened due to melted plastic parts, parts that got too hot due to 
the current running thru parts next to them. In some switches those 
parts now appear to be made of metal, so that may fix this problem.  

Remember: Coincidence does not imply causality. I think it's likely 
that we just started using DoT-5 about the same time that our OG 
switches started to run out of lifetime. I just ordered some new 
German (FTE) switches. They are expensive, but I thought they might 
be better quality, so I may install one of them in my rebuilt MC. 
Then we get to see how long it lasts. Of course it's also possible 
that the new German switches are nowhere near the quality of the old 
ones. If any of you would like to try some of them, I can sell them 
for $18 plus shipping.

In the meantime, if you are still using DoT-3 or 4, you should do a 
complete fluid flush every 2-4 years, just to reduce the corrosion 
that happens as that fluid absorbs moisture. Leaving old DoT-3 or 4 
in a system for a long time is just asking for major brake expense 
down the road.

DoT-5 does not absorb moisture, so periodic flushing is not 
necessary, and it's a much better rubber to metal lubricant, so the 
seals last MUCH longer.

BTW, when I called to buy the new German switches, I asked the 
salesman if they were really better than the cheap ones. His answer 
was that they get a lot fewer complaints about them. That could mean 
nothing, but there's at least the implication that there are people 
out there having trouble with modern cheap switches and DoT-3 and 4 
fluids, too. If that's the case, it would be unfair to blame the 
DoT-5.

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