From: Ryan Gill (rmgill@mindspring.com)
Date: Thu Jul 04 2002 - 13:37:57 PDT
At 8:41 AM -0700 7/4/02, Nathan Wilkens wrote:
>First, thanks for all the info.... Now, a follow up question:
>
>I understand that a brake system with seals designed for DOT 5 brake fluid
>would be damaged by the use of DOT 3 or 4. I also understand that a system
>made for DOT 3 or 4 can be 'upgraded' to DOT 5 with minimal risk of damage.
Not quite.
DOT 3 will eat natural rubber seals. DOT 4 will not. DOT 5 or DOT 4
may be used in the same system if the system is flushed before you
use the other in it. The mix of the two makes a milky substance that
stops working as very well as brake fluid.
>Is it fair to assume that since a CUCV is basically a civilian vehicle
>first, it would have a brake system designed for DOT 3 or 4, and that Uncle
>Sam just put DOT 5 in it? I'm hoping the answer is yes, because I've had
>mixed brake fluids for at least 9 months now (since I bought it, but who
>knows how long it was mixed before) with no leaks and no reduction in
>performance.
The big problem with the DOT 3 in a DOT 5 spec system is the DOT 3
will eat the seals _if_ they are natural. Since you don't have leaks,
I'd flush it out and renew with either spec. Which ever works. Use
DOT 4 or DOT 5. You may also want to use DOT 5.1.
Something I posted a while back about Brake Fluids...(if anything
needed to be in a FAQ this does. It keeps coming up).
FYI there is a DOT 5.1 (poly glycol ether based) that has the
properties of DOT 5 (silicone) with compatibility with DOT 3 and 4
(also poly-glycol-ether based but with lower boiling points).
According to the Vintage triumph Register's, DOT 3 has issues
with natural rubber seals and will eat them.
http://www.vtr.org/maintain/brake-fluids.html
Further details on types of Brake Fluid and the differences
between what the Euro's call DOT 5 and what the us calls DOT 5.1 or
DOT 5.
http://www.belray.com/consumer/Q&A%20pages/q&abf.html
http://www.rpmnet.com/techart/fluid.shtml
>Incidentally, when flushing out the old stuff, many of you have recommended
>using isopropyl alcohol to scrub out the mixed fluid, then using an air
>compressor to blast it clean. I don't have good access to an air
>compressor - can I just pumped the alcohol through and leave it open to dry
>out? Or should I skip the alcohol step entirely if I don't have an air
>compressor (or am I overlooking some obvious means to gain pressurized
>air?).
Get a couple of cans of compressed air or one of those portable tanks
and use that. Having an air compressor is a boon to automotive work.
Now that I have one, I can't believe I ever got along with out it.
You want to make sure you get rid of the alcohol before adding the
new fluid. I doubt the DOT 4 will have too much of an issue with it,
but the DOT 5 could find it a problem.
--
--
Ryan Gill rmgill@mindspring.com
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