# Brake fluid change interval car vs motorcycle

Discussion in 'The Garage' started by Project84, Oct 10, 2017.

1. ### Project84I can haz adventure?

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Curious, why so many people stress the importance of motorcycle brake fluid change intervals (annually seems to be the most common) and yet, of all the car forums I've been a member of for years and years, of all the shade tree mechanics I've known and worked with, of all the used cars I've helped people buy/fix, no one ever speaks about brake fluid change intervals on them.

Why do people stress the importance on a motorcycle and seemingly (with life experience to validate this claim) ignore the brake fluid in their car/truck?

Is it because we're on 2 wheels instead of 4 so brakes are a little more important?

I don't understand the logic. With a speed bleeder (pneumatic or pump type) the process on a car takes 30 minutes or less. Why are so many people ignoring that and yet, I've always been preached to about motorcycle brake fluid being an annual or bi-annual necessity?
2. ### alexwn00b

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The main reason to change brake fluid is because of water absorption. Are bikes more likely to absorb water?
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3. ### Project84I can haz adventure?

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See, that's the real question.

A given commuter car has twice the number of brakes but lets keep it simple and say they have the same number of brake pistons.

Car - 2 piston calipers on front, single piston calipers on rear = 6 pistons.
Bike - 2 piston calipers on front, (1) 2 piston caliper rear = 6 pistons.

Brake calipers are built essentially the same. Same rubber boots and internal parts. Same steel pistons.

The car will see 50x the amount of rain/snow/salt as a bike will, so it would be expected the brake fluid interval (for fear of contamination) would be much higher on a car.

Yet, we never hear people discussing that scenario.
4. ### ohgoodJust givver tha berries !!!

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the brake fluid reservoir on a bike is rained on constantly. car reservoir will never see rain.

bike brakes are manipulated much more frequently than car brakes and wear out pads ten times faster.
5. ### ragtoplvrLong timer

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I think car systems are heaver and more robust than on a motorcycle, and have a greater volume of fluid per seal.

Also if my car brakes fail and I crash, most of the time I can walk away.

On a bike any failure of brakes, or other parts usually results in pain.

That makes me more proactive about bike maintenance. In a perfect world, there would be no difference.

Rod
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6. ### Project84I can haz adventure?

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Getting rained on doesn't = leaking.

I don't buy it.

As for using the brakes more often, again I'm not buying it. If anything I use the brakes of my bikes less often because I'm more prone to downshift/engine brake and make a turn without using brakes at all.
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7. ### Project84I can haz adventure?

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See, this is a valid statement and makes sense.
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8. ### Project84I can haz adventure?

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I'd still like to ask to any of you who change bike brake fluid annually, do you ever change car/truck brake fluid at all?

Honestly....?
9. ### cabnfvrBeen here awhile

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Interesting. i'd go for the bike reservoir being more open to the elements (many rear reservoirs vent to atmosphere!) along with more aggressive use. It's OK if someone doesn't buy the more aggressive use aspect, but if I drove the Jeep like I do the bike it would be off road far more often than it is used to.

I change the bike brake fluid every two years. I should probably change the Jeep as well but it's only been 5 years so....
10. ### txndncowboyBeen here awhile

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Cause the owners manual says to and I always do what I'm told by experts.
11. ### C SquaredNow with TURBO!Supporter

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Part of the cycle thing is some use DOT5 which isn't water absorbing so change more often.
Many cars recommend every 2 years. People don't do it.

The valid argument is similar access points for moisture to get let in but the car holds a lot more fluid so the car will take longer to contaminate.
The rate at which the fluid breaks down is probably very similar between the two.
You can test for moisture with one tester and fluid breakdown with a test strip.
Then, you know and are not just being proactive.
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12. ### MotoChris521expert apprentice

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People are cheap . Lots of maintenance issues are ignored on automobiles because the car operates normally . Industry standard is usually every two years for brake fluid , but rarely gets done . And newer cars with ABS can involve more intensive service procedures (i.e. bleeding the modulator ).
13. ### KustomizingKidBeen here awhile

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There are two aspects, water absorption and heat breakdown... Moto's have much smaller capacities making both of these much worse. Also do you really want your breaks going out on your bike? I will say that if people had their brake fluid flushed every other year (my recommendation unless you live in AZ or another other desert climate) your brake pads would last longer and the odds of needing a caliper or master replaced would go down drastically. It all really boils down to how well do you want to maintain your shit.
14. ### usgserLong timer

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Not saying I'm always 100% on schedule but my schedule is annually on bikes and two years on my cars and trucks. Not only to lessen the risk of brake failure from contaminated fluid. Not only is water logged fluid a safety concern, internal brake parts do rust, corrode, get gunked up and are expensive to replace. If you're too cheap or lazy to do maint please leave the wife and kids at home and ride solo.
15. ### ragtoplvrLong timer

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Yes, every presidential election year, since I can not stand to go near a TV
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16. ### adam728Long timer

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Manual for both my bike and car say every 2 years.

When racing I used to change the bike fluid several times a year. Now I am lazy. Coming up on 3 years of ownership and I've never even bled them yet. Automobiles get a fluid change when a line rusts through. I should probably get better on both again.
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17. ### eakinsButler Maps

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My master cylinders have a metal cap and rubber seals in the cap. How is moisture coming in there?
18. ### GSWayneOld Guy nOObSupporter

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Moisture can permeate through any rubber parts like the flexible portions of the brake lines, the piston seals, and the rubber membrane that covers the fluid in the master cylinder. The rate of permeation is temperature dependent, so the brake fluid should probably be changed more in hot humid areas.

And like most people I change the fluid on my motorcycle much more often than my car.
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19. ### ydargMiscreant

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Consider that a bike holds a few oz. A given car probably holds a quart +.

Contamination becomes more of an issue with the tiny amount of DOT fluid that a bike has to work with.
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20. ### C SquaredNow with TURBO!Supporter

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That and the accordion style top seal is designed to severely limit the absorption of water.
But, some still gets in. Condensation inside the dust boot etc. very small amounts get past the seals.

If I pour brand new brake fluid in a cup in my classroom at the start of the day, it will test bad for moisture before the end of the school day.
AC climate controlled. That is in hours unsealed. So, a year or two some gets in.