When to bleed brakes

I'm getting the 90k service on my 96 Integra LS, and the dealer wanted to
bleed the brakes. I ended up going to an independent shop and they say they
just replace the fluid in the reservoir unless there is some problem with
the brakes.

When do you bleed your brakes?

 

I'm with the dealer on this one. Brake fluid is a kind of alcohol.
Like all alcohols, it is mutually soluble with water. Every time the
system is opened, (for example, to add fluid) some water is absorbed
by the brake fluid. Eventually, the amount of water in the fluid is
enough that it can begin to cause problems, such as internal
corrosion. So, I am an advocate of periodic brake system flushes. 90k
miles sounds about right to me.

The process is simple, but can be messy and uses a lot of brake fluid.

Elliot Richmond
Freelance Science Writer and Editor

 

Thanks for your reply.

Wouldn't changing the fluid in the reservoir dilute any water present in the
system?

 

Yes, I think it would, but the fluid in the lines and wheel cylinders
could still be contaminated. It would take awhile for it all to mix.

Elliot Richmond
Freelance Science Writer and Editor

 

Once per year.

If you only replace the fluid in the reservoir, that does nothing about the
fluid in the master cylinder bore, whihc is under the reservoir. Inside the
bore is where corrosion will occur first, since that's the entry point for
water into the system.

In order to replace the fluid in the master cylinder bore, you need to
bleed at the wheels.

Most master cylinder failures are due to neglect.

 

Not for a looong time.

Reservoir fluid only makes its way into the master cylinder bore and the
lines as the brake friction linings wear.

You cannot "dilute" the water in the system. The water settles out into the
lowest points, which are usually the master cylinder bore, wheel cylinders
and caliper bores. It's not like you were stirring milk into coffee or
something, it's more like oil and water (even though brake fluid is not
actually oil).

When the water has been there long enough and the fluid is old enough, the
bores start to rust. You'll get a skinny black strip of corrosion at the
very bottom of the bore. That's what tears up the seals and causes leaks.

 

I'd have to agree with TeGGer on this one. When I was a service writer for
a Honda dealership we advised our customers to flush the brake system every
30,000 miles. That's what Honda recommends (or used to, anyway. It's been
awhile).

 

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Bleeding brakes takes only a small amount of fluid, way less than a
quart. It's even a bit of fun to do with a helper, since it's so cheap
compared to having it done at a shop. You can immediately see the old
stuff come out, and the brakes will feel 'firmer'. The joy of saving money.

'Curly'

 

Fun it is, until that instant the hose pops off the fitting and you get a
shot of fluid all over the place.

And that warm feeling you get when it finally turns a clear, light straw
color... ;-)

 

About 8 years ago I got that warm feeling after a brake fluid flush on
my brother's VW. The warm fuzzy feeling turned cold and prickly when we
realized the master cylinder got messed up in the process. And the
warning was right there in the Bentley manual (Bentley is to VW what
Helm is to Honda) "Do not push the brake pedal all the way to the
floor".

 

Agreed. In my experience, the most contaminated fluid is in the wheel
cylinders, so a proper flush is what's needed. What's in the reservoir
is nice and clean compared with what is out at the wheels.

 

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My 'helper' is well-trained, (she knows to keep the pedal away from the
'nether reaches') but if I was hiring a goof-ball, I'd put the chunk of
2x4 under the pedal. I also suck the reservoir empty with a new turkey
baster from the $0.99 Store, to save pumping all that 'depleted' stuff
thru the lines. Front-left, front-right, rear-right, rear-left. (Helm's)

BTW, TeGGer . . . Your 'warm feeling' description sounds like a
check-up at the urologist. . . Stay loose, eh?

'Curly'

 

That warning may be for VWs and for cars with neglected brake systems. If
your Honda is less than 6 years old or so, it's perfectly OK to floor the
pedal when bleeding, and is in fact desirable, since it sweeps the front of
the MC bore and keeps it clean.

Some loose. It's -30C right now. Any "warm feeling" would be decidedly icy
at the moment. Brrrr.