Re: D.O.T. 3-4 vs. D.O.T. 5 for a '56 Patrician

Posted by Tim Cole On 2015/9/15 15:47:33
There are a lot of assertions going around about DOT 5. I have some first hand experience.

a) Does Dot 5 react with Dot 3 and 4 with damaging results?

Results: When I was in Africa they were always dumping DOT 3 into military vehicles with DOT 5 because they didn't know any better. We never had to do a single repair on a vehicle because of that.

b) Does Dot 5 turn Dot 3 into sludge?

Results: I took a clear plastic bag with DOT 3 and DOT 5 and hung it on the wall for a couple of years. When I was asked about the issue I showed them the demonstration. The DOT 5 is inert and simply sat there separated from the DOT 3.

c) Does DOT 5 cause hydraulic brake switch failure?

Results: I have had such failures with both DOT 5 and modern DOT 3. However, I have a vial of 55 year old DOT 3 and it is not the same as modern DOT 3. The old brake fluid was a Castor oil base while the new stuff is glycol-ether. To my recollection those switches didn't give the frequency of problems in the old days as today. In fact, I don't ever remember having to replace one.

Hope this helps.

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