When to Replace Brake Fluid?
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Joined: Apr 2007
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How many actually change brake fluid in their cars? Havn't done a single car in my 40 years of driving. Unless major work is done, it aint needed. It's a none compressable fluid and don't change. It can't absorb moisture in a close system unless you drive around with the cap off as it's not vented to atmosphere. There is nothing special with a Harley that needs periodic fluid changes.
Ron
Ron
Big Kahuna HDF Member
Joined: Feb 2006
Posts: 23,881
Likes: 34
From: USA
Guys I don't care what you say...I bled my brakes at 2 years on my bike which takes DOT4 and mixes with water unlike your DOT5. Greenish brown fluid came out of the caliper...the brake master cylinder was barely down but the fluid was contaminated in the caliper. Every one of my cars...same thing the fluid at the caliper is always cloudy & dirty...this is for the last 20-30 years.
Next time I do it....I'll post a photo...you won't believe it.
Next time I do it....I'll post a photo...you won't believe it.
Big Kahuna HDF Member
Joined: Feb 2006
Posts: 23,881
Likes: 34
From: USA
An NHTSA survey found that the brake fluid in 20% of 1,720 vehicles sampled contained 5% or more water
DOT 4 fluid, which has a higher minimum boiling temperature requirement (446 degrees F dry and 311 degrees wet) soaks up moisture at a slower rate but suffers an even sharper drop in boiling temperature as moisture accumulates. Three percent water will lower the boiling point as much as 50%!
Water contamination increases the danger of brake failure because vapor pockets can form if the fluid gets too hot. Vapor displaces fluid and is compressible, so when the brakes are applied the pedal may go all the way to the floor without applying the brakes!
DOT 5 also cannot disperse moisture that enters the system throughout the fluid like DOT 3 and DOT 4 fluids. Any water that does get inside tends to "slug" and settle to the lowest point in the system, which is usually the calipers and wheel cylinders. Slugs of pure water are not something you want inside a brake system because they concentrate corrosion and increase the risk of pedal fade if the water gets hot enough to boil (it only takes 212° F to turn liquid water into steam).
DOT 4 fluid, which has a higher minimum boiling temperature requirement (446 degrees F dry and 311 degrees wet) soaks up moisture at a slower rate but suffers an even sharper drop in boiling temperature as moisture accumulates. Three percent water will lower the boiling point as much as 50%!
Water contamination increases the danger of brake failure because vapor pockets can form if the fluid gets too hot. Vapor displaces fluid and is compressible, so when the brakes are applied the pedal may go all the way to the floor without applying the brakes!
DOT 5 also cannot disperse moisture that enters the system throughout the fluid like DOT 3 and DOT 4 fluids. Any water that does get inside tends to "slug" and settle to the lowest point in the system, which is usually the calipers and wheel cylinders. Slugs of pure water are not something you want inside a brake system because they concentrate corrosion and increase the risk of pedal fade if the water gets hot enough to boil (it only takes 212° F to turn liquid water into steam).
Last edited by KBFXDLI; Feb 13, 2009 at 09:43 PM.
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Joined: Jan 2008
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From: On one of 10,000
Why a Turkey (baster)?
Someone asked...
When doing a system flush, the baster is used to remove some (but not all fliuid from the master cylinder. This helps to prevents spills along with covering your bike with towels. It also lessens the amount of new fluid needed to flush the master cylinder, lines, and calipers.
I wonder how a turkey would taste deep fried in Dot 4? That would be an expensive turkey!
When doing a system flush, the baster is used to remove some (but not all fliuid from the master cylinder. This helps to prevents spills along with covering your bike with towels. It also lessens the amount of new fluid needed to flush the master cylinder, lines, and calipers.
I wonder how a turkey would taste deep fried in Dot 4? That would be an expensive turkey!
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