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After finally getting the tub off my M38A1 jeep, (see Forum "wanted" ,M38A1body tub wanted), its great to gaze at all the now easily accessible areas to work on. But I can also see some of the next set of problems, excuse me, "issues" that I will be facing. One of which is the brake system, which has, like so many other systems that have sat for awhile, deteriorated due to the moisture absorbed in the brake fluid. Why can't we use hydraulic or ATF instead of brake fluid or expensive silicone fluid? This would illuminate the water problem and the system would last a lot longer. It is, after all, a hydraulic system. Yes, in modern vehicle disc brake systems, the fluid sits very close to the pad that can get very hot. But how hot due the wheel cylinders actually get in our old jeeps? Not very, I suspect, and probably not over 200 deg F that ATF is still able to deal with. Seems to me the rubber seals would get damaged before the fluid would. Any other reason besides temperature that prevents the use of an oil based fluid in our brakes?

There is a whole debate as to which is better. Some people swear by silicone break fluid as the break fluid itself does not absorb moisture from the air. Moisture will still get into the system and will seek the lowest point which is the salve cylinders. The debate is to how long this takes verses regular break fluid.

If you go with regular fluid you need to discipline yourself to flush the system with new fluid every one or two years. If you do this regular fluid will be just as good as silicone.

Petroleum based fluids are just as susceptible to water intrusion as DOT 3 & 4. I am an aircraft mechanic by trade and they use MIL-H-5606 red oil based hydraulic fluid in their landing gear systems and their brakes. This fluid does not absorb moisture like Dot 3 & 4 but is much more flammable than Dot 3 & 4.