Why should I flush my brake fluid every year, you ask? - PeachParts Mercedes-Benz Forum

240 Ed · #1 05-29-2002, 12:54 AM

:EDIT: Mercedes Benz Factory Service Recommendation is every two years. :EDIT:

I shall give my standard lecture on brake fluid, for those who may have mercifully missed it! Ha, Ha too late! YOU MUST READ ON...

Brake fluid is hygroscopic = Means it LOVES water.
Huh? where does it get water...?

There is a tiny hole in the master cylinder cap which allows atmospheric pressure to equalize when the level drops due to pad wear. Eventually over the year, the fluid becomes diluted with water. This water can cause rust in the system, but a worse fate than that awaits!
(wait for it)

Brake fluid has a certain boiling point. DOT 3 has a lower point than the later DOT 4. (NEVER USE DOT 3) DOT 5.1 has the highest.
DOT 5 is silicone fluid and does not absorb water, and is not included in this discussion.

Okay, here is what happens. Water dilutes the fluid, right? Right.
Unfortunately, water boils at a lower temp than brake fluid, so the boiling point of the brake fluid is now lowered.
Why is this important?
In normal use, you won't notice the difference. Brake feel stays the same. Even if you were to use straight water!
The problem comes with intense use, say coming down a mountain side with sustained braking (and pulling an enormous 80 ton yacht, say).

Your calipers heat up with the attendant friction (normal). But now, because of the compromised brake fluid, the fluid starts to boil! What happens when the water in the fluid boils?
That's correct, you get STEAM!!! Steam is a gas! gas does NOT work well at all as a hydraulic medium!!!
What happens to your brakes?
NOTHING!
It is known in the trade as "brake fade". (one of several types)
No matter how hard you press on the pedal, you won't get any more brake. You will probably start to speed up as you are going down hill. The press folks call this "...he lost his brakes"

There you have it.
Change your fluid at least once every other year (in dry climates) and if you live in Louisiana or some humid place, once a year.
Pain in the butt, huh.
Your choice, but you are now informed and can now bore other people with said lecture.

tcane · #2 05-29-2002, 01:15 AM

240 Ed:

I could not have said it better! In addition, water in brake fluid = rusting/corroding brake componets = failed brake components because of the rust/corrosion = at a minumum poor braking because componets do not move like they should (like the caliper piston not pushing on the brake pads with full force) = brake components needing R&R long before they would need to be but for not changing the brake fluid. Absorbtion of atmospheric moisture causes brake fluid to turn opaque and tells the aware owner to replace the brake fluid. I use my Mighty Vac to R&R the brake fluid every year, doing it when the humidity is low - like the M-B owners and service manuals call for.

Tom

rino · #3 03-11-2007, 09:50 PM

Quote:

Originally Posted by tcane

240 Ed:

I could not have said it better! In addition, water in brake fluid = rusting/corroding brake componets = failed brake components because of the rust/corrosion = at a minumum poor braking because componets do not move like they should (like the caliper piston not pushing on the brake pads with full force) = brake components needing R&R long before they would need to be but for not changing the brake fluid. Absorbtion of atmospheric moisture causes brake fluid to turn opaque and tells the aware owner to replace the brake fluid. I use my Mighty Vac to R&R the brake fluid every year, doing it when the humidity is low - like the M-B owners and service manuals call for.

Tom

Hey Tom, I drive a 240D, both brakes and clutch share the same fluid and fluid reservoir... I just changed the fluid, bled the brake lines... Then it occurred to me: that same old fluid corrodes/rusts not only the brake lines and components, but also the clutch lines and components... should I also replace the fluid in and bleed the clutch lines? I asked that in another thread today and the consensus (only two readers answered my question) was: don't mess around with the clutch, it is a bucket of worms for the first timer... If you live in a dry climate and the old brake fluid was pretty clear, forget about it... leave the clutch alone.

Just curious, how do you (and others here) feel about it?

Thanks,
Rino

sokoloff · #4 03-11-2007, 10:54 PM

I bleed the clutch every year when I do my brakes. The fluid coming out of it is usually much dirtier than what comes out of the brake lines. I use a pressure bleeder - makes it very easy.

Stevo · #5 03-12-2007, 12:19 AM

Quote:

Originally Posted by sokoloff

I bleed the clutch every year when I do my brakes. The fluid coming out of it is usually much dirtier than what comes out of the brake lines. I use a pressure bleeder - makes it very easy.

How do you do the clutch with the pressure bleeder? It does seem like a good thing to do but I've always done the clutch with the brake slave, hose to clutch slave thing.

rino · #6 03-12-2007, 09:28 AM

Quote:

Originally Posted by sokoloff

I bleed the clutch every year when I do my brakes. The fluid coming out of it is usually much dirtier than what comes out of the brake lines. I use a pressure bleeder - makes it very easy.

So you are saying it's easy... I wonder what was all that talk about the "bucket of worms..." In your opinion, as a beginner (I have never done clutch flushing, obviously), where am I likely to encounter the most difficulty?
Do you think it feasible to do the clutch flushing procedure without a power bleeder, just by opening up the bleeder valve and letting the fluid out (one-man flush)?
I did it this way a few days ago with the brake line and it worked wonderfully... no problems at all!

Thanks for your input,
Rino

sokoloff · #7 03-12-2007, 10:31 AM

I use the pressure bleeder for clutch and brakes. The last nipple I do is the one on the clutch. With the pressure bleeder still attached to the brake fluid reservoir and opening the bleeder nipple on the clutch, it flows out nice and steady. Once it's clear, close it up and you're done. Never tried it any other way.

Arthur Dalton · #8 05-29-2002, 09:23 AM

Hygro...

engatwork · #9 05-29-2002, 09:08 PM

I'm with ya'll on this. Every failure I have ever seen (outside of running the pad backing into the rotors, which I have really never seen) was caliper failure because of not changing the fluid.

gsamuelson · #10 05-30-2002, 01:15 AM

Amen!

I have only been driving newer vehicles until lately and so I never thought much about brake fluid. When I received my Unimog it had a leaky wheel cylinder. Changed the cylinder and bled the system. The crap in the main bowl was scary! The crap that came out of the lines was UGLY!!!!!!!

Just did the front brakes on my 300CD and again, UGLY!! brake fluid that looks like swamp water. I am starting to wonder if anyone ever changes their brake fluid? (present company excluded, of course).

For all those who have not changed their brake fluid, DO IT!! It is like the old Fram commercial, you either pay me now, or pay me latter. A few bucks of fluid is alot cheaper than wheel cylinders or master cylinders. My unimog wheel cylinder was $200CDN, OUCH!

rickjordan · #11 05-30-2002, 04:47 AM

Just curious as to why I have never heard of changing brake fluid until I got into German cars. My VW calls for brake fluid change every 2 years. I mentioned changing the brake fluid to co-wprker who owns a Ford, and he said he has never done that and has had no problems.

winmutt · #12 03-12-2007, 11:51 AM

Quote:

Originally Posted by rickjordan

Just curious as to why I have never heard of changing brake fluid until I got into German cars. My VW calls for brake fluid change every 2 years. I mentioned changing the brake fluid to co-wprker who owns a Ford, and he said he has never done that and has had no problems.

"Found On the side of the Road Dead"....

When was the last time you saw a W123 on the side of the road dead? Perhaps MB owners tend to be more meticulous about maint because they (mostly older models) will last more or less forever?

I never changed my ps or brake fluid on my accord, at 200k whats the point? However I know my diesels will make it to 400+ with ease and even then I will probably rebuild the engine or replace it.

Shawn D. · #13 03-12-2007, 12:06 PM

Quote:

Originally Posted by winmutt

When was the last time you saw a W123 on the side of the road dead?

This weekend.

dieseldaddy · #14 05-30-2002, 08:34 AM

My wife is beginning to hate this forum.
Now I have something ELSE to do on our MBs!

Just how does one change the brake fluid? Would I suck it out the top or is there a drain?

Does anyone use DOT 5.1? Should I stick with DOT 4.

Do you have to 'bleed' anything? If so, how?

(Boy, too many question this early in the morning...)

Thanks guys!

Jim Anderson · #15 05-30-2002, 11:05 AM

If water in the brake fluid is bad why did they use a hydroscopic fluid? Why not hydraulic fluid for hydraulic brakes?