Re: Brake Fluid to use


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Posted by David Sherman [24.32.202.83] on Monday, March 22, 2010 at 14:59:55 :

In Reply to: Brake Fluid to use posted by Andrew Moore [170.35.224.64] on Monday, March 22, 2010 at 14:46:14 :

I will be curious to see if anyone suggests DOT 4, which is supposed to be compatible with DOT 3, but better in some way. Mostly, the choice is between DOT 3 and DOT 5. DOT 3 is what we've all used forever. It absorbs water over time, which gets distributed throughout the system and gradually makes things rust. Thus, it should be flushed out from time to time. DOT 5 does not absorb water, but if water gets in the system, it will end up in the lowest spots and make those spots rust faster than the same amount of water would if distributed throughout the system. The main application for DOT 5 is high-performance vehicles where the brakes may get very hot. It will take more heat than DOT 3. I can't see why this could possibly be any benefit at all on our old trucks with their slow speeds and oversized drum brakes.

The two fluids cannot be mixed, so since you have a fresh system, now's the time to decide what you want to put in it. DOT 5 is a bit more viscous and is harder to get all the bubbles out of. I use DOT 5 in my M35s only because that's how they came from the government and I won't want to purge the system. Plus I got a few gallons of government surplus DOT 5 back when they were still selling hazmat stuff to the public. Personally, I can't see any shining reason to pay 4X as much to put DOT 5 in a vehicle that was designed for DOT 3 and doesn't need any of DOT 5's high performance advantages. The two fluids have different sorts of water/rust issues, but neither one is rust-proof, which means you need to change the fluid from time to time in either case. That argues for using the cheap DOT 3 so you can purge until all traces of water and rust are out without having to pump $30 worth of fluid through the system just to purge it. I also like the fact that, since DOT 3 mixes with water, I can hose off any spills.



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