[T3] Brake Fluid
Jim Adney
jadney at vwtype3.org
Wed Dec 6 15:20:58 PST 2017
Brake fluid is something that most of us very seldom think about, but it's very
important and there are some things that you should know about it.
Most cars in our era came with DoT-3 brake fluid, but our cars, at least the
late ones with disk brakes, came with DoT-4, which has a higher boiling
point. The original stuff was made by ATe (Alfred Teves) and was blue. It
was beautiful stuff, but it's hard to find and it's pricey once you find it. Both
DoT-3 and 4 have the same basic chemical composition as antifreeze. It's
not exactly the same stuff, but it's important to understand that it's not a
petroleum product. They are completely miscible with water, which makes
water the ideal fluid to clean them up with.
These standard fluids work okay, but they have some drawbacks:
They are hydroscopic, so they absorb water out of the air. Because of this,
they should be flushed and replaced every few years with fresh, dry, brake
fluid. Mixing brands is no problem.The brake fluid in most cars has never
been replaced. This causes problems in 2 ways. "Wet" brake fluid boils at
lower temperatures, the wetter the lower. this means that a lot of hard
braking can lead the the loss of stopping power when your brakes get hot
enough to boil the fluid.
The second problem is that damp brake fluid becomes corrosive and causes
rusting of the internal surfaces of your brake parts. This is especially a
problem in disk brake calipers, where a small amount of fluid will seep past
the seals, get exposed to the air and get "wet" and cause corrosion just
outside the piston seal.
Those of you who know me know that I've long been a fan of DoT-5 Silicone
Brake Fluid. DoT-5 is chemically different. It does not mix with water and it
does not absorb water, so it does not need to be changed, ever. Silicone is
also a MUCH better rubber to metal lubricant than the other stuff, so master
cylinder piston seals now last forever. You can buy DoT-5 at your FLAPS.
The downside of DoT-5 is that it is expensive and somewhat more difficult to
install correctly. Also, because it doesn't mix with water, it's hard to dispose
of. I recycle it myself and use the recycled stuff to flush the next car, but
that's more than most people will want to do. I'll take your dirty stuff, but I
don't know how a good way to ship it would be.
I've used Silicone Brake Fluid in all my air cooled cars since 1977, and I'm
completely sold on it. It's upside is that it has reduced my need to do brake
work on my own cars by at least 95%. It has also meant that when I get a car
out of storage, I never have to worry about whether the brakes will still work.
Note: DoT-5 is NOT a good metal-to-metal lubricant, so it's use in cars with
ABS is not recommended (because of the ABS pump.)
I have a file on using and installing DoT-5 in your car. Email me if you want a
copy.
So here's the take-home message: Use DoT-5 if you can, but if you don't
want to do that, use DoT-4 and flush and replace it at least every 4 years.
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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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