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Probably a dumb question, but here goes...

Getting ready to flush the brake and clutch systems on a 2018A. How much brake fluid should I have on hand so I don't run out during the procedure?

Dan

This is a hard decision. How frugal are you and how adverse are you to waste?

A 32 oz bottle will be more than you need for anything short of knocking an open bottle over. Once a bottle of brake fluid is open any remainder should be tossed. You will be tossing a fair amount of fluid with the 32 oz bottle, it will be more than enough.

A 12 oz bottle probably won't be enough so you would buy two. Two 12 oz bottles cost a couple of bucks more than one 32 ouncer. Two 12 oz bottles will probably be enough in most cases with a bit left over.

If you use a vacuum pump and simply pump at the bleed nipples, get the 32 oz. If you use a vacuum pump and empty the fluid reservoir then wipe the reservoir clean before adding clean fluid for bleeding you will probably be ok with two 12 oz bottles. If you use speed bleeders and wipe the reservoir clean two 12 oz should be ok.

If you buy two 12 oz bottles you run the risk of making a second trip to the supply store. With a 32 oz bottle no matter what you will be throwing away some.

It doesn't take a lot of fluid to flush the clutch but the fluid will probably be nasty. The rear brake doesn't take much more than the clutch. The ABS metering block doesn't hold much fluid if you are ambitious enough to flush it too.

I'm pretty sure the correct answer to this is like knowing the one best engine oil or the one best tire

Lol, that gives me a good idea. Is it okay to mix the Yamaha brake fluid with "Auto Zone" DOT4 fluid? Of course, the shop manual says "No, absolutely not"...

Dan

As long as you are mixing unopened regular Dot 4 brands or are flushing one brand of regular Dot 4 with another brand of regular Dot 4 there should be no issue. You shouldn't mix Super Dot 4 or Dot 4 Low Viscosity with regular Dot 4.

Thank you!

You can mix. Many buy too much fluid and have to toss it if they don't keep it sealed up.... being your '18 ain't that old, it ain't needing repeated flushes... surprisingly each system holds little... 8 oz. bottle should be enough. Get a 12 if you must. If your bike was old and never done for a few years, well, more flushing required. Yes you can mix brands, they all have to be compatable except for DOT 5.1. Any DOT4 will go with another DOT4, no worries. If you do it annually like you 'should' (according to me, including cycling the ABS pump), you'll not need that much.

I've got your ABS test connector, so that will get done at the same time. I've got just over 18 month and 15600 miles on the bike.

Dan

raYzerman wrote: ↑Thu Jul 25, 2019 3:34 pm You can mix. Many buy too much fluid and have to toss it if they don't keep it sealed up.... being your '18 ain't that old, it ain't needing repeated flushes... surprisingly each system holds little... 8 oz. bottle should be enough. Get a 12 if you must. If your bike was old and never done for a few years, well, more flushing required. Yes you can mix brands, they all have to be compatible except for DOT 5.1. Any DOT4 will go with another DOT4, no worries. If you do it annually like you 'should' (according to me, including cycling the ABS pump), you'll not need that much.

I have found that 1 x 12 oz bottle is enough without a lot left over, unless it has been too long since the system was last refreshed. (I usually use more than 8 oz. but depends on how much of a hurry I am in and how crappy (especially clutch) the system is.) I start by using a syringe to remove everything I can from the reservoir and then a dry shop towel (low lint) to mop it out and sop up any residual particulates. Fill reservoir and flush until clean fluid is coming out.

Regarding DOT brake fluids...
Technically, DOT 5.1 is compatible with DOT 3 or DOT 4. However, DOT 5 is not. DOT 5 is a hydrophobic silicone-based fluid and will not absorb water which is why it is used for some applications - rarely for normal automotive/motorcycle operation. According to Wikipedia:
Silicone based fluid is more compressible than glycol based fluid, leading to brakes with a spongy feeling. It can potentially suffer phase separation/water pooling and freezing/boiling in the system over time - the main reason single phase hygroscopic fluids are used.
Anyway, there is little need to use anything other than DOT 4 on your bike - that is what the system was designed to use. (DOT 5.1 has a bit higher boiling point and lower viscosity compared to DOT 4.)

While we are told to throw out an opened bottle of brake fluid, I have been known to keep it for up to a year. The stuff is hygroscopic (absorbs water from the air) but will be OK if very WELL sealed and stored in a cool, dry place. I usually try to get just enough for the task at hand.

Note: Some manufacturers make a point that their brake fluid (DOT 4) is "Synthetic" (and presumably better than the other stuff). ALL brake fluid (at least DOT 3, 4, 5, 5.1) is synthetic.