Re: [T3] Brake Cylinder Paste?

[Jim Adney <jadney@vwtype3.org>]

On 21 May 2008 at 0:57, russw wrote:

> On Tue, 2008-05-20 at 17:45 -0500, Jim Adney wrote:
> 
> 
> > Okay, so no one ever told you what was in the official paste?
> > 
> > I think the ATe packets contain a silicone grease. It's compatable 
> > with the rubber and it doesn't absorb brake fluid. Brake fluid is 
> > perfectly compatable with the rubber, but when it absorbs water it 
> > tends to promote corrosion. 
> > 
> > I use Dow-Corning #33 silicone grease, medium consistency, which 
> > seems to work well, but I've wondered if I could add something to it 
> > that would help retard corrosion. I was thinking that zinc powder 
> > might work by acting like the surfaces were galvanized. It may be 
> > hard to buy zinc powder, however, because I think it's quite 
> > flammable.
> > 
> > I'm now on my 2nd tube of #33, but a tube would last most people a 
> > lifetime. It's actually quite a large tube, about the size of a jumbo 
> > tube of toothpaste.

> Hmmm, I use the #44 and the #55 greases here for various purposes. I use
> one of them for distributor lub and the other is an O-ring lube for
> hydraulics. The o-ring lub does warn that is will make some rubber
> swell.  We had the problem at work that it would swell the seals and
> make the air cylinder sticky, so we switched to a Loctite lub that didnt
> bother the rubber. I have a tube of that too, (gee, I forgot to empty my
> tool box when I retired), and I will get you the number off it.

It's probably true that ANY lube will be incompatable with SOME kinds of 
rubber, so we always have to be careful when choosing a lubricant. I'm not 
familiar with #44 and #55, so I don't know what they are, but the #33 seems to 
work fine with the rubbers that are used in brake systems. That MIGHT mean that 
it's no good with rubbers that are compatable with dino hydraulic fluids; I 
don't know.

For example, it's interesting that silicone lubes are NOT compatable with 
silicone rubbers. They make them swell too much.

At www.dowcorning.com I found that DC 33, 41, and 44 are all in the same 
family, and that they are all made of lithium soap and silicone oil, which 
should make them perfectly fine with brake parts, as well as with most other 
non-silicone rubbers. They are specifically made for extreme temperature, both 
high and low, bearing lubrication.  Both 33 and 44 are available in either 
light or medium consistency. I've tried both, and don't have an opinion on 
which is better for brakes.

DC 55 is much the same, but with the addition of an ester, which may be what 
makes the O-rings swell. A small amount of swelling is desirable, but they say 
that you need to test it with your material to make sure that it's appropriate. 
It looks like this would be a bad choice for brakes.

-- 
Jim Adney
jadney@vwtype3.org
Madison, WI USA

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