Brake fluid question - Star Motorcycle Forums: Star Raider, V-Max, V-Star, Road-Star Forum
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post #1 of 21 (permalink) Old 04-20-2018, 08:08 AM Thread Starter
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Brake fluid question

Ok guys, and gals, I have read it here many times about changing your brake fluid. I know many of you suggest it every so often. WHY? Its fluid inside a sealed system. Unless you overheat it or damage a component some how I don't see the reason to replace it. Now granted I am more of a "if it ain't broke don't fix it" kind of guy but I do preform regular basic PM, oil and filter as well as plugs and air filters but I have never replaced brake fluid. I know the manual suggests it but car manuals also suggest replacing tranny fluid, and engine coolant periodically. Both of which I have never done. Someone please explain the reasons why I should do it. I for one have never heard of an accident or vehicular problem because "his brake fluid was old and worn out" If it TRULY needs to be done I will do so but to me it's one of those things that once I am done I will be telling myself, "Well that was a waste of time. No purpose at all in what I just did" I will be doing my normal spring service soon so if I am going to do it now would be the time.

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post #2 of 21 (permalink) Old 04-20-2018, 08:24 AM
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Primary reason for brake fluid is that it absorbs water. The water dilutes into the alcohol and lowers its boiling point (on hot disk brakes water actually would boil in the calipers).

Water will also cause corrosion in all your internal brake mechanisms.

How does the water get into a sealed system? Thats a good question. On a car the reservoir has a vent to let in air as the level drops. Where does it go if the brakes are not leaking?

A lot of that is subjective, but I can tell you this: if you flush the brake fluid out of your bike after several years it will be dark yellow to almost brown. New brake fluid is nearly clear.

So something is happening to it, and the engineers that designed your bike think it should be flushed out and replaced every few years.

Maybe its not so much the fluid breaking down - maybe its stuff that corrodes off the brake components that need to be flushed out.

Its normally a very easy thing to do, except for the current recent 'Certainly not a rookie...' thread where the poster ran into some strange problem bleeding the fluid thru.

One thing: when you flush your brakes buy a new bottle of brake fluid - apparently just sitting half empty on the shelf in your garage for several years will degrade what is left in the bottle.
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post #3 of 21 (permalink) Old 04-20-2018, 09:11 AM Thread Starter
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Thanks for the input KCW, Yeah I know it discolors over time and like you I have heard it adsorbs moisture. Granted I am not a engineer or scientist but I have always wondered how a sealed system is going to absorb moisture.

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post #4 of 21 (permalink) Old 04-20-2018, 09:49 AM
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The main infiltration point for this is the piston rubber gaskets.
normal limit is 2% to 3% water absorption.

The higher quality fluid, normally absorbs water faster. DOT3 is the lowest, but also has the lowest boiling temp. DOT4 is higher, boiling temp, but absorbs water alittle faster. DOT5.1 is the next step up.

DOT5 is completely different and NOT compatible with other DOT fluids, your system must be flushed completely clean, they really just suggest you replace everything. It doesn't absorb water. This is what HD normally uses, or used to use.
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post #5 of 21 (permalink) Old 04-20-2018, 03:29 PM
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Water gets in the system from the air that is trapped in the reservoir.. even when you have it full there is an air gap..anytime you remove the cap to top it off air gets in..Even simple expansion of the reservoir can allow minute amounts of air in. Though it seems odd to get moisture in this system..it does. Water will make your brakes feel soft or spongy. For the 1 liter you have to buy every couple years it's a cheap maintenance item to do and maintain the braking systems . Unlike a car you only have 2 brake points..and if one fails.. oh oh.

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post #6 of 21 (permalink) Old 04-20-2018, 09:56 PM
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you're not even supposed to use brake fluid from a bottle that's been kept for over a year; the general rule of thumb is to immediately throw away the unused fluid as soon as you're done. just the small amount of air inside the used bottle contains enough moisture to break down the fluid inside.

i can appreciate the "if it ain't broke don't fix it" motto. but this is scheduled maintenance. the idea is to replace things BEFORE they fail so they don't fail later while you're using them or cause damage to vital parts. you change your engine oil, right? why change that but not your transmission fluid? so you replace your brake pads before they wear completely down and fail on you when you're trying to slow down before hitting a busy intersection. replace your brake hoses before they deteriorate to the point they start losing pressure as you're trying to stop before hitting a busy intersection. you replace your brake fluid to keep your brakes working exactly as they are supposed to so you know that every time you intend to stop, your bike complies accordingly.

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post #7 of 21 (permalink) Old 04-21-2018, 07:44 AM
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you can drive an old beater car and fix things as they break or fail with the possible exception of suspension components

Ive know a couple people that have seen wheels rolling past their car, and realized it was theirs

but on a motorcycle your life is on the line - if something fails on a MC that will be you rolling down the highway at 70mph.

You want your MC to be 100% all the time.

Of all the bad things that can happen to a motorcycle, having your front caliper corrode, start to drag, overheat and then seize and lock up the front wheel - I think that may be #1. You are going over the handlebars.

8 ounce bottle of DOT 4 at Walmart: $4.
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Last edited by KCW; 04-21-2018 at 08:15 AM.
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post #8 of 21 (permalink) Old 04-21-2018, 07:34 PM
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The breaks feeling spongy is the lest of your issues normally, it just increases your stopping distance.

The real issue is it lowers the boiling point, and when that water boils in the break line, due to using the breaks and building up heat, it will expand and clamp your breaks SOLID on, and you will not be able to unlock your wheel.

https://youtu.be/wkO2QBFWpPM?t=40
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post #9 of 21 (permalink) Old 04-21-2018, 07:43 PM
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great story about wrecking his bike, gear saved his life.

I bought my first full set of gear from a sales guy that hit a deer at 60mph. Was able to walk away. Has all his gear on a rack at the motorcycle shop where he works. Side and face shield on his full face helmet looks like someone was testing an angle grinder on his head.
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post #10 of 21 (permalink) Old 04-22-2018, 01:10 PM
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Quote:
Originally Posted by KCW View Post
great story about wrecking his bike, gear saved his life.

I bought my first full set of gear from a sales guy that hit a deer at 60mph. Was able to walk away. Has all his gear on a rack at the motorcycle shop where he works. Side and face shield on his full face helmet looks like someone was testing an angle grinder on his head.
Although this guy was wearing some proper gear, this is a pretty gnarly vid.
https://youtu.be/iXSvQxiQYOY
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