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Why do we need to change brake fluid?


flying_monkey

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flying_monkey

First, let me say that I'm new to BMWs, having my 04 R1150RT for just over 3 months. It's wintertime, too cold (for me, at least) to ride here in Reno, so I'll put my flame suit on, and ask something I've been wondering about. Why do we have to do this? Is changing the brake fluid required on BMW cars? I have a 15 year old truck with 100k on it, it has never needed to be changed. I've had many other motorcycles with hydraulic brakes that didn't recommend this. So why do only BMW motorcycles require this? Are these brakes substandard to cars or other bikes in some way?

 

Ed

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The reason is that brake fluid hygroscopic meaning that it will absorb water, it does this as the brake fluid heats up and cools down(condensation from air drawn in around seals and threads). The color change in your brake fluid is caused by oxidation of the components in your brake system. removing the oxidized fluid is the reason to change, regardless of make model or type.

 

Some manufacturers figure that you my keep their products longer than others. I guess.

 

hope this helps.

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As has been said, brake fluid absorbs water, reducing its boiling point and leading to corrosion of ferrous metal parts in the brake system. On the R1150xx bikes, the wheel circuits are vented to atmosphere and so absorbs more moisture than normal.

As for never changing fluid on other vehicles - most vehicles I have own do recommend it, just not as frequently. On my car for instance, the recommended interval is every three years.

 

Andy

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Motorcycles do tend to get parked seasonally. The water will corrode the internals of expensive parts like the ABS unit, causing their pistons to seize. Rule of thumb is that if you use clear brake fluid, change it when it starts to look like the color of urine (morning, not after your 6th beer). ;)

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Another problem motorcycles have is the exposure to light because of the clear reservoirs. You can make some difference just sucking out the old dirty stuff and replacing it. Having the dealer or well practiced mechanic replace all the old crud in the brake system give you a set of brakes you will really enjoy. The proverbial 2 finger stops. A thing of joy!

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Along with the water absorbtion, and other points made above, BMW was pretty innovative with the use of ABS on its bikes......And the ABS/power brake unit on your bike is very fiddley, mechanically. Lots of possible problems are avoided by keeping the life blood of that system from sludging up.

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It's wintertime, too cold (for me, at least) to ride here in Reno

 

You mean I have to stop . . ? ;)

 

I have an '04 RTP, currently at Spanich Springs. I'll be riding into town this afternoon.

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Very good points, but with all that said...why do you not have to do this (or so it seems)to 4 wheel vehicles?

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Very good points, but with all that said...why do you not have to do this (or so it seems)to 4 wheel vehicles?

 

You really should. I do. There is better weather protection, and larger volume in 4 wheelers, but it eventually becomes contaminated. Especially in wet (Humid) climates.

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You will find that most cages using DOT3/4/5.1 require 2 year fluid change intervals. The exception are those using the newer D0T5 Silicone fluid. I change the fluid in our D0T3 or D0T4 cages every 2 years and it takes about 30 minutes per vehicle :thumbsup:.

I also use Ate Typ200 or Ate Super Blu in both bikes and cages, as they have higher wet and dry boiling points than regular DOT3 and D0T4 fluids.

 

And, being a persnickity bugger, brake fluid ADSORBS water :thumbsup:

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Talking with my auto mechanic / ducati rider about this very topic, he suggested that the big difference in the fluid change intervals between, say, a Dodge and a BMW bike, probably has more to do with BMW being a "premium" brand, liability issues and the like, than with some significant difference in the mechanics involved. YMMV.

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I agree with Andy on the points he presented. I've had cars and a Moto Guzzi motorcycle with dragging disc's and fresh fluid many times fixed the problem. As to the frequency for the BMW servo brakes, I find the interval disappointingly short also. It's the drawback of this particular servo design. One qualifier, I assume BMW is being ultra conservative on the 2 year fluid change requirement that has to cover all the machines sold. A GS ridden through streams off road and an RT ridden high mileage all year long in all kinds of weather would be the extremes needing the most attention. Only occasionally do I ride in the rain when on a trip and my bike is garage kept. I would speculate not really necessary for a 2 year interval at my 5,000 mile/year mileage. As mentioned a visual on the fluid is an indicator on the fluid's condition. Unfortunately the two hidden reservoirs on the ABS unit that actually activate the calipers are not visible for inspection without the tank removed. As a baseline my rear control circuit's fluid was the most visibly turned at a 4 year 20,000 mile change. I also only use Dot 4 with it's higher boiling temps.

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Afternoon Ed

 

As mentioned above moisture entering the brake fluid is the main reason for the requested brake fluid change. Dot 3 takes in more moisture than Dot 4 but Dot 4 doesn’t handle the moisture as well as Dot3 does once it enters the system.

 

A lot of foreign car manufactures still give a time or miles for brake fluid service. Most American auto companies stopped requiring brake fluid changes years ago. The main reason is special brake fluid with anti moisture additives to better handle moisture (at least GM uses this type fluid) plus the fact that most American companies have switched to more expensive and more robust brake hose material to not allow moisture to wick through the brake hoses. At one time moisture entering through the brake hose rubber was the biggest entry point. GM now uses a new type of rubber brake hose with an EPM lining and special outer jacketing. That plus the anti moisture brake fluid additive have essentially eliminated moisture problems on the newer vehicles.

 

Even BMW has entered the premium brake hose age by using special Stahlflex brake lines on the later 1150RT’s and the hexheads. That also drove the fluid change intervals up to 2 years on the wheel circuits and 4 years on the control circuits.

 

Also keep in mind that a lot of BMW motorcycles are still sold in Europe and AFAIK they are still doing brake fluid moisture testing at annual vehicle inspection on vehicles in some European countries.

 

When I was testing brakes at Pikes Peak years ago we could boil brake fluid at high altitudes even under normal braking loads if any moisture in the fluid was present.

 

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Talking with my auto mechanic / ducati rider about this very topic, he suggested that the big difference in the fluid change intervals between, say, a Dodge and a BMW bike, probably has more to do with BMW being a "premium" brand, liability issues and the like, than with some significant difference in the mechanics involved. YMMV.

 

Probably true. I have yet to see a significant color indication of contamination, but with the cost of the parts involved with

BMW bike, I will happily do the 2 year dance, (Since I am capable of doing it myself) rather than pay for the replacements......Or a roadside problem. YMMV.

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Ed,

Interesting post...

 

"So why do only BMW motorcycles require this? Are these brakes substandard to cars or other bikes in some way?

Bike 21, 04 R1150RT

Bike 20, 90 K75(gone)

Bike 19, 86 XT-600

Bikes 1-18, gone, but not forgotten

They all taught me something."

 

Guess there is one thing all those bikes didn't teach you... TO CHANGE YOUR BRAKE FLUID REGULARLY!!! :D

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Every vehichle I have owned I think had a schedule for various service items, including Ford, Chevy, and Toyota trucks and they all had a list of XXX miles to change oil/trans/diff/...and all had a schedule for brake fluids, at some point.

 

BMW bikes is NOT the only one. It is cheap insurance. I know it can be time consumming and a PITA on the servo bikes, but I hear it is not too bad once you figure it out. It is pretty easy on my 1100RT non servo bike.

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flying_monkey

Actually, I too live in Spinach Sprigs. :-) And I did ride to work in Sparks this morning, as well over to the other side of Reno during lunch. Lovely day!

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I had a ford ranger pick-up that I never changed the brake fluid on. I think I changed the brake calipers at least four times. I didn't know why at the time.

If you have a brake caliper seize up on a bike, think of what that could cost.

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If you changed the calipers four times, then you must have bled the air out of the system each time. So you are adding at least some new fluid.

 

Unless you meant changing the pads.

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Somebody said the brake reservoirs in some BMW models breathe fresh air. My bike has a clever bellows system that allows for expansion and contraction with the sealed system but it doesn't seem to admit fresh air to the system in any way I can see. Am I mistaken?

 

Perhaps related, dirtrider says the water in brake fluid seems to boil more readily at higher altitudes. For sure, water boiling on a stove boils at lower temp, as every high school kids learns. But how does that work inside a braking system during braking (very high pressure) and during rolling?

 

What does the boiling, water held by the chemicals which are in DOT4 or water in ordinary form when all the chemicals are already fully filled with water?

 

Do stainless steel brake lines slow down water adsorption, if i have the term right, when introduced as replacements for rubber lines in older bikes?

 

Very interesting to learn that changing the fluid in the reservoir is almost as good as doing a whole system change and bleed. I gather doing that simpler task once a year or so might be equivalent to a full change and bleed (and with peel-the-paint spills) every two years?

 

Ben

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Somebody said the brake reservoirs in some BMW models breathe fresh air. My bike has a clever bellows system that allows for expansion and contraction with the sealed system but it doesn't seem to admit fresh air to the system in any way I can see. Am I mistaken?

 

Perhaps related, dirtrider says the water in brake fluid seems to boil more readily at higher altitudes. For sure, water boiling on a stove boils at lower temp, as every high school kids learns. But how does that work inside a braking system during braking (very high pressure) and during rolling?

 

What does the boiling, water held by the chemicals which are in DOT4 or water in ordinary form when all the chemicals are already fully filled with water?

 

Do stainless steel brake lines slow down water adsorption, if i have the term right, when introduced as replacements for rubber lines in older bikes?

 

Very interesting to learn that changing the fluid in the reservoir is almost as good as doing a whole system change and bleed. I gather doing that simpler task once a year or so might be equivalent to a full change and bleed (and with peel-the-paint spills) every two years?

 

Ben

Morning Ben

 

Somebody said the brake reservoirs in some BMW models breathe fresh air. My bike has a clever bellows system that allows for expansion and contraction with the sealed system but it doesn't seem to admit fresh air to the system in any way I can see. Am I mistaken?

 

Yes, the reference was to the IABS controller reservoirs (inside the ABS computer itself) as those systems have a long vent tube on each reservoir venting them to atmosphere.

 

Perhaps related, dirtrider says the water in brake fluid seems to boil more readily at higher altitudes. For sure, water boiling on a stove boils at lower temp, as every high school kids learns. But how does that work inside a braking system during braking (very high pressure) and during rolling?

 

Not always at high pressure as the brakes are not on continuously. Even so once the water turns to steam it creates air bubbles in the brake fluid that doesn’t compress completely during brake apply )To save a lot of typing just Google wet vs dry brake fluid. The wet boiling points are always lower than the dry (new fluid) boiling points, with enough moisture in the fluid the boiling point is quite low at high altitude..

 

 

What does the boiling, water held by the chemicals which are in DOT4 or water in ordinary form when all the chemicals are already fully filled with water?

 

I have no idea just that dot 3/4 brake fluid takes in moisture easily and the more the moisture content the lower the boiling point. It’s down right scary on how much moisture gets in through seals and rubber brake hoses.

 

Do stainless steel brake lines slow down water adsorption, if i have the term right, when introduced as replacements for rubber lines in older bikes?

 

Depends on the stainless steel brake line liner. If just a rubber membrane or plastic liner then not much better than conventional rubber lines. Some of the Teflons are better with some of the newer high tec entries being almost as good as solid metal lines.

 

Very interesting to learn that changing the fluid in the reservoir is almost as good as doing a whole system change and bleed. I gather doing that simpler task once a year or so might be equivalent to a full change and bleed (and with peel-the-paint spills) every two years?

 

This I don’t subscribe to. No doubt that any amount old fluid removal is removing some moisture but the real problem areas are down in the ABS controller and calipers so just changing the fluid in the reservoirs isn’t accomplishing much. It does help to suck most of the old fluid out of the reservoirs prior to doing a proper system bleeding but just sucking the fluid out of the reservoirs is no replacement for a proper full system bleeding.

 

 

 

 

 

 

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Very interesting to learn that changing the fluid in the reservoir is almost as good as doing a whole system change and bleed.

I hope you don't think the fluid at the handle bar and brake pedal reservoirs is going to your calipers. :dopeslap: Not the case for the servo system. That fluid is just the control circuit going to the servo under the gas tank. The servo unit has it's own reservoirs that supplies pressure to the calipers.

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I thought that stainless lines were just rubber lines sheathed in stainless mesh, which limits the amount of expansion of the rubber under pressure, giving a firmer brake feel.

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I thought that stainless lines were just rubber lines sheathed in stainless mesh, which limits the amount of expansion of the rubber under pressure, giving a firmer brake feel.

 

Morning NonComp

 

I haven’t seen SS lines using plain rubber liners for years. I suppose if you search long enough and cheap enough you might still find something. Probably more in line with trans cooler hoses or oil cooler lines.

 

Anymore, not much in the SS brake flex hose area that isn’t Teflon lined or some type Teflon derivative or other high tec moisture impervious liners used in SS flex brake lines.

 

In fact a lot of the SS brake hoses from the last few years are not only Teflon lined (or similar) but also have a PVC or other outer protective coating on the outside of the SS sheathing.

 

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What does the boiling, water held by the chemicals which are in DOT4 or water in ordinary form when all the chemicals are already fully filled with water?

 

Very interesting to learn that changing the fluid in the reservoir is almost as good as doing a whole system change and bleed. I gather doing that simpler task once a year or so might be equivalent to a full change and bleed (and with peel-the-paint spills) every two years?

 

Ben

 

Water is heavier than brake fluid, and tends to settle into the lowest parts of the system, especially when enough has infiltrated the fluid for it so come out of solution. So corrosion is not evenly distributed through the parts.

 

Years ago, I bought a project pickup that had been neglected. It had drum brakes with 2 wheel cylinders per wheel (Mazda drum brakes). The bottom cylinder on each wheel had been frozen solid with internal rust for a looonnngg time.

 

 

Consequently, I would discount the idea of just changing the reservoir fluid. And the concentration of water at the calipers would seem to indicate that the fluid would boil first at the wheels, even if it does so first when the brakes are released. This would blow all the fluid out of the lines all the way back to the reservoir. Just sayin'.

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First, I believe that conventional glycol-based brake fluid (DOT 3, 4, 5.1) aBsorbs water rather than aDsorbing it as was previously posted. Adsorption would better describe how silica gel or activated carbon works.

 

Although DOT 5 fluid, being silicon based, will not absorb water, that doesn't mean that water isn't still able to enter the system. This could cause problems with freezing, boiling, or corrosion of the system components. It seems a benefit of using a hygroscopic fluid over a silicon-type would be that water would absorb over time rather than pool in the system, and you just change out the fluid at regular intervals before its performance is compromised.

 

Another reason for regular change intervals would be to refresh the additives and corrosion inhibitors that are added to most brake fluids, just like with antifreeze and engine oil.

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