Re: [FWDLK] DOT 5

["Dave Homstad" <dhomstad@xxxxxxxxxxxxxxx>]

I think the secret of success with DOT 5 is how clean you get the system before you put in the DOT 5. You can not just bleed in DOT 5. The entire brake system must be flushed of all old DOT 3 (or DOT 4) fluid. This means rebuilding all wheel cylinders and the master cylinder, and flushing the lines with alcohol and blowing/drying  the alcohol out with compressed air. If this is not done, then small amounts and films of DOT 3 will cling to the walls of the pipes and cylinders. DOT 3 does not mix or dissolve with DOT 5 (like water and oil). So flushing with DOT 5 will not remove these small traces. DOT 3 is heavier and will eventually, over time, sink to the lowest point of the system: the wheel cylinders. Small amounts of moisture vapor that are present at the wheel cylinder seal interface will be absorbed by the DOT 3. DOT 5 would repel this moisture. But since there will only be a small quantity of DOT 3 present at the wheel cylinder, it will quickly become saturated, because the moisture cannot be dispersed and diluted into the larger fluid volume of the entire system. The result is rust and corrosion! 

I found this out the hard way on my daily driver. Two years after bleeding in DOT 5, a caliper started to stick. I always bleed a system before I work on it so that I get the dirt out before putting in new cylinders. When I bled this caliper, there was a half ounce of very dark DOT 3 in the jar under the clear DOT 5.

Another major contributor to wheel cylinders going bad is galvanic corrosion that takes place, in the presence of moisture,  between the dissimilar metals of the iron cylinder and aluminum piston. This is why the iron rusts and the aluminum pistons get crusty and pitted, resulting in pistons stuck in the sludge. Mopars in the 50's, at least on my 56 Dodge, had anodized pistons (mine are cherry red). Anodize is an anticorrosion coating for aluminum, and is a barrier to the galvanic cycle. Car and parts manufacturers do not presently use this process. Why this is not a legal safety requirement I do not understand! Anodized pistons would last much longer and only cost a penny extra a piece. I guess the parts replacement and service industry has a stronger lobby than Ralph Nader. This is just one of my pet peeves.

Dave Homstad
56 Dodge D500


-----Original Message-----
From:   Larry C. Stanley [SMTP:peerless@xxxxxxxxxxx]
Sent:   Sunday, August 01, 1999 6:27 PM
To:     L-FORWARDLOOK@xxxxxxxxxxxxx
Subject:        [FWDLK] DOT 5

All,

The military also uses DOT 5. The main difference in a military and a
civilian brake setup is the military is a totaly sealed system and the
fluids are changed out on a more frequent basis than is done on civialian
cars. When was the last time you had the brake fluid changed on your daily
drivers? Brake fluid is not a permanent fluid.

The silicone fluid will not absorb the moisture that can get in the system.
Any moisture will lay on the lowest part of the system and start to rust.
DOT 3 and 4 will absorb any moisture at the expense of boiling point, but
if the fluid is changed occasionally that will never be a problem.

Regular bleeding (on a system that has not been serviced in a long time)
will not get the all of the contaminated fluid out (especially not the DOT
5) because the bleeders are at the top of the cylinders and are for letting
out air. Water would be at the bottom. About the only way to fully change
the fluid is to tear down the wheel cylinders and dry them out. This is a
lot of work and is why it is seldom done. But it is a very good time to
inspect all parts of the system.

I have the brake fluid changed every time I have shoes or pads put on my
daily drivers. All of my '58s get DOT 5 when the brakes are reworked. DOT 5
will not attack paint like the DOT 3 and 4 will. As little exposure to the
weather as most of our cars get, the DOT 5 should not cause a moisture/rust
problem.

Larry