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ATVC Correspondent 10-22-2018 12:45 AM

Answered: Brake System Fluid Change

This week our editors were asked if changing out hydraulic disc brake fluid is really necessary if you've been up on your brake maintenance:

Big Frank 10-22-2018 01:14 AM

Before I clicked on the link I was thinking that brake fluid is hygroscopic and that's why you're supposed to use a new bottle of fluid ever time you need some. Hygroscopic means it pulls moisture out of the air. Hydrophillic basically means something that easily mixes with water. I didn't think about what that moisture is doing inside the brake system. I just added changing brake fluid to the list I made of maintenance that needs to be done before winter. I'm glad you posted that.

ATVC Correspondent 10-22-2018 11:26 PM

Good call, Frank. The hydrophillic comes from the fact that newer brake fluids are being constructed out of silicone molecules (like DOT 5) so as to be
hydrophoebic and actually repel water molecules.

Trouble is, as you accurately pointed out, the hygroscopic nature of the fluid means the water will still be getting absorbed. It just won't blend the way it does with traditional mineral oils. We're not entirely convinced this is a good thing.

Either way, right on. We added the term to the original article.

Big Frank 10-25-2018 01:48 AM

I knew if I posted enough I'd eventually get something right. Even a blind squirrel finds a nut once in a while. ;)

I wasn't thinking about DOT 5, and didn't know any ATVs or UTVs came with it. I've only used Dot 3 and DOT 4 for both my on-road and off-road vehicles. I've seen DOT 5 recommended for antique cars but read that you can't use it in newer cars with ABS. I didn't know it was hydrophobic, which would be good for a vehicle that sits a long time. Like my ATV that's been sitting outside for 10 years, much of that time uncovered. You can replace DOT 3 with DOT 4, and I've topped off DOT 3 with DOT 4 with no problems, but you can't mix DOT 5 with any of the older brake fluids.

Yoakum 03-04-2019 05:10 PM

I'm going to open myself up for ridicule here, but being married I'm used to it. :)
In my MX days, I was going into a sand corner hot and low sided flat on my face. Did this about three more times before finding out my front brake was locking up.
Thing is, there was no corrosion, sticking, gumming or anything else. Everything moved freely.
Asking around I was told that brake fluid that's wet, when put to hard use (as in racing), will actually get the moisture hot enough to vaporize and instantly lock your brakes.
I changed the fluid and the problem went away.
So...was somebody pulling my leg or has anyone else ever heard of this?

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