65 brake fluid

[Mike M.]

Re: 65 brake fluid

in 1974, i sent the calipers off our low mile 65 for stainless sleeving. at that point, i used silicone brake fluid. 35 years later and no evidence of leakage. i use silicone in all my restorations. have crossed the rockies several times with silicone brake fliud in c-1 and c-2's and didn't loose brakes at those elevations. mike

[Dan D.]

Re: 65 brake fluid

Okay, you guys are making me feel better about DOT5. Maybe I will try it. Not worried so much about Billy's master cylinder, but the China wheel cylinders are a big unknown. I don't plan on driving this car far, wide, or too fast (ha-ha), so if the wheel cylinders start to hang up I should have some prior feeling of it. I have heard that the petal may be a little spongy, not to worried about that either. But I did not know DOT5 still entrained moisture. I guess that just means it will collect at the lowest point in the line??? -Dan -

[Terry M.]

Re: 65 brake fluid

But I did not know DOT5 still entrained moisture. I guess that just means it will collect at the lowest point in the line??? -Dan -

I have read four SAE papers about DOT5, and none of them mention it trapping moisture, but I didn't stay in a Holiday Inn last night. Glycol fluid absorbs moisture right through the rubber of the hoses as well from the atmosphere in the master cylinder because it has a chemical affinity for moisture. DOT 5 is just the opposite and it repels moisture. One of the tests for determining the fluid in a brake system is to draw off some of the fluid and pit it in a jar with some water. DOT5 will not mix with the water -- there will be a separation of the two layers. Glycol fluid will absorb the water and there will be no separation of the fluids.

DOT5 is slightly more compressible than glycol fluids, but for most of us doing street driving that will not be an issue. On the race track, with a well trained driver, that might not be comfortable -- but serious racers change brake fluid often and the prominence of DOT5 is no advantage in that environment.

I have seen some cans of DOT5 that will lead you to believe you can flush the old glycol fluid out of your brake system with DOT5. Do NOT believe it. One of those SAE papers was a test of that method of installing DOT5 done by the military in Panama. After three years a black gel-like scum was found in the systems that simply had DOT5 flushed through to remove the glycol. There was no evidence that scum did any harm to the military vehicles they tested, but it seems counter productive to me. I want the inside of my brake system to look like Jim's picture.

I have had DOT5 in my 1970 for over 25 years. I flushed it once in that time just because it seemed like the thing to do. Try that with glycol.