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Discussion Starter #1
My 2011 RT has not had its brake fluid changed for nearly 3 years now. I know, but I’ve not hardly ridden it because of circumstances (personal, Covid, life, Etc). It’s mid season summer here in the UK and still riding opportunities galore but it’s been C-19. Will the fluid deteriorate to the point of becoming dangerous to ride?
 
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When it gets old it absorbs moisture and will eventually turn into a snotty consistency. It can clog parts of the brake system and cause corrosion. For all a bottle of fluid costs I would just change it. First time is a little daunting but it isn’t rocket science either. If you have enough moisture and ride hard enough you could have the moisture boil ending up with no effective brakes, unless you going down a mountain or riding hard on a track it shouldn’t really be a problem.
 

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Brake fluid will absorb moisture from the air over time. The seals keep it to a minimum, but it still happens.
Standard advice is to replace every 2 years, I'm not sure what BMW suggest. The same goes for a bottle of brake fluid once it's first opened.
It doesn't really matter how much you have ridden it, but if it's been sitting outside, or in a humid / moist atmosphere, or ridden in the rain a lot that won't help.

With moisture in the brake fluid, there are a couple of possible problems.

1 Corrosion of the inside of the brake system, which can lead to the brakes seizing on or off, weeping seals etc.

2 Brake fluid with high moisture content has a much lower boiling point, so if the brakes get hot, (during repeated hard braking, such as a track day, or fast riding on a windy road) b, the fluid can develop bubbles of gas leading to sudden lack of bite from the brakes.
 

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Discussion Starter #4
I suppose I am thinking ‘can I leave it to next year and have BMW do it?’. I do most things on the bike just haven’t done the brakes - abs system and kit looks a bit complicated.
 

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I suppose I am thinking ‘can I leave it to next year and have BMW do it?’. I do most things on the bike just haven’t done the brakes - abs system and kit looks a bit complicated.
At your own risk, I'd say you'll be fine to leave it to next year, if riding in a typically relaxed touring bike style.

The two year rule is pretty much the same for all vehicles for the last 40 years, regardless of the quality of the seals.
The seals on my old Land-Rover's brakes are nowhere near as good as those on any modern motorcycle. the wheels are expected to get dunked in water on a regular basis, and then stop a heavy vehicle with a 3 tonne trailer, and they still recommend new fluid every 2 years.

If you are DIYing, then you can get DOT 5.1 fluid that has a higher boiling point even when "wet" and can be used to replace the standard DOT 4 without a full flush. The Fluid manufacture small print will state you should still follow the original vehicle service intervals.

(do not use DOT 5 / 5.0 - it is not compatible with other types, and you must completely flush the system before using it)
 

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I suppose I am thinking ‘can I leave it to next year and have BMW do it?’. I do most things on the bike just haven’t done the brakes - abs system and kit looks a bit complicated.
You probably can, BUT you should know that flushing the fluid for the RT is very easy, to the extreme! You can do it yourself, since you have done everything else! Refer to this thread for more information: Brake fluid flush question

Brake fluid gets degraded at just 2 locations on the system. It gets badly degraded and burnt at the caliper end, where it is subjected to high heat from braking friction. The other location is at the reservoir, where it is somewhat exposed to the air, and since DOT 4 brake fluid is very hygroscopic, it will absorb any moisture in that air. What's wrong with moisture in the fluid? Not much really, UNTIL that moisture gets to the caliper end where it will turns into bubbles of steam, when exposed to the high temperature of braking! The bubble of steam will feels like having bubbles of air in the system (spongy feels to the brake). How long does it take for the moisture to get from the reservoir, where it is absorbed, to the opposite end of the caliper? A very, very long time, even in the most humid air! The moisture contaminated brake fluid will be limited to the reservoir until that volume is completely saturated before it will start to propagate down the line. Think about it, when was the last time that you had done a fluid flush in your car? Any issues with the brakes?
 

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Color is a good indicator of condition and moisture content. If it is still clear or a light golden color in the master cylinder, just bleed the system to exchange what is in the calipers and get some rust (if any) out.
If it is brown, a full flush is on order.
 

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Discussion Starter #8
“Think about it, when was the last time that you had done a fluid flush in your car? Any issues with the brakes?”

Well, that was my thinking. So - help me out with a level of risk out of 10.
 

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“Think about it, when was the last time that you had done a fluid flush in your car? Any issues with the brakes?”

Well, that was my thinking. So - help me out with a level of risk out of 10.
Check your maintenance manual for your car I'll bet it recommends replacing your fluid at some interval. Bottom line it it absorbs moisture and it causes rust in the lines and calipers. An auto has one to two quarts of fluid and four wheels to brake with. A motorcycle has only a pint or two at best and only two wheels to brake with. Obviously you have never looked at the internals in a cars brake system. I have replaced several master cylinders on cars that I have acquired due to rust failure. Level of risk? That is up to you. I personally flush all my vehicles at least every three years and the crap that comes out is really bad. Why would you not want the best possible fluid in a system that can save your life?
 

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Check your maintenance manual for your car I'll bet it recommends replacing your fluid at some interval. Bottom line it it absorbs moisture and it causes rust in the lines and calipers. An auto has one to two quarts of fluid and four wheels to brake with. A motorcycle has only a pint or two at best and only two wheels to brake with. Obviously you have never looked at the internals in a cars brake system. I have replaced several master cylinders on cars that I have acquired due to rust failure. Level of risk? That is up to you. I personally flush all my vehicles at least every three years and the crap that comes out is really bad. Why would you not want the best possible fluid in a system that can save your life?
Agree completely. My car, truck and motorcycles gets their brake flush every 2-3 years.
 

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The reason BF flushing is now a scheduled maintenance procedure to protect ABS components in cars or bikes. As JZ noted above, things like master cylinders fail from the seals wearing. If the fluid is kept clean and free of gritty substances, the components will last nearly indefinitely. Rust and debris getting into ABS solenoids is the issue that's really going to cost you.

We sold brake fluid flushes regularly in my shop. Those who didn't do it were the ones who eventually had hydraulic or ABS issues.
 

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“Think about it, when was the last time that you had done a fluid flush in your car? Any issues with the brakes?”

Well, that was my thinking. So - help me out with a level of risk out of 10.
I'll help you out. Brake fluid that has high moisture levels due to lack of proper maintenance will probably function normally. The problem lies when you brake repeatedly and the fluid starts to heat up. This is were boiling points are very important to be educated on. So if you have excess moisture in the brake fluid and you start riding your brakes the brake fluid temperature will rise to a point where the moisture will boil and generate steam. Now this steam is a gas and gas is compressible. At some point your braking affect will diminish and the brake lever will fade and get spongy because your compressing the steam from the boiling water mixed in with the brake fluid. You may think all is well with normal braking but get when you start to heat things up you will realize that you might get in a bit of a scare down the road. Another issue is old fluid with moisture mixed in will over time start corroding metal parts it comes into contact with.
My suggestion is don't be cheap or lazy in proper maintenance of your machine. Pay someone to flush your brakes if your not able to properly perform this task yourself. It's one of those maintenance tasks that needs to be done as scheduled.
 

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I agree. It's 95% about the boiling point of the fluid which is reduced as moisture content increases. I did my wife's Optima at about 60,000 miles (about 5 years) and I have yet to do my Durango (65k and 3 1/2 years) but I do my RT religiously at 24 month intervals (I'm late now by about 3 months but I've only ridden about 1,200 miles this year since I've been working from home). Why? Well, mainly because it's so easy to do on a bike. You don't even have to flush the ABS actuator. If I was you, I'd just do it. It's like $5 and takes an hour (tops) of your time.
 

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I just changed mine, which was 5 years old. It was slightly darker then the new one. Difference..??? no change in the feel to the front, but a noticable change to the rear i.e, less spongy.
 

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Break fluid needs to be replaced every two years.
Not doing the maintenance is just an accident waiting to happen.
Do you really want to take that risk?
Ed.
 

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“Think about it, when was the last time that you had done a fluid flush in your car? Any issues with the brakes?”

Well, that was my thinking. So - help me out with a level of risk out of 10.
0
 

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Check your maintenance manual for your car I'll bet it recommends replacing your fluid at some interval. Bottom line it it absorbs moisture and it causes rust in the lines and calipers. An auto has one to two quarts of fluid and four wheels to brake with. A motorcycle has only a pint or two at best and only two wheels to brake with. Obviously you have never looked at the internals in a cars brake system. I have replaced several master cylinders on cars that I have acquired due to rust failure. Level of risk? That is up to you. I personally flush all my vehicles at least every three years and the crap that comes out is really bad. Why would you not want the best possible fluid in a system that can save your life?
No argument about it at all, I also flush my brake fluid quite religiously every 2 years, especially since it's easy to do.

Technically though, the moisture absorption only happens at the reservoir, the only place where the fluid is exposed to the air. Now, I don't know what it's like in the reservoir of the LT, but for the RT, the surface of the fluid in the reservoir is pretty much "protected" from contact with the air by a blanket of flexible rubber that extends pretty much from edge-to-edge, which leaves really tiny gap for the air-to-fluid contact! Furthermore, any moisture that is attracted to the fluid will be retained in the reservoir until the whole amount in there is saturated. There is no mechanism to make the moisture propagate into the brake circuit. Chemistry won't do it, and mechanically when you use the brake, only a small amount of the fluid, from the bottom of the reservoir, is pumped into the circuit, only to return to the reservoir when you let go of the brake! Why is it important to note that the fluid at the bottom of the reservoir gets pumped into the circuit? Look up the value of the specific gravity of the DOT 4 fluid. If it's greater than one (which it is) it will be denser than water. Therefore, and fluid that had attached itself to water will tend to float on top of the denser fluid!

Having said all that, I maintain that you should flush the brake fluid at regular interval, and it IS very easy to do, especially on an RT, with the non-servo and pass-through ABS circuit! No reasons to take any risks.

EDIT:

PS: John, I saw in another thread that you had gotten a brake fluid tester. Take a reading of the fluid in your reservoir, and another one from a small amount that you bleed from your caliper. I am sure that the two readings will be quite educational.
 

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The reason BF flushing is now a scheduled maintenance procedure to protect ABS components in cars or bikes. As JZ noted above, things like master cylinders fail from the seals wearing. If the fluid is kept clean and free of gritty substances, the components will last nearly indefinitely. Rust and debris getting into ABS solenoids is the issue that's really going to cost you.

We sold brake fluid flushes regularly in my shop. Those who didn't do it were the ones who eventually had hydraulic or ABS issues.
Excellent point, especially with the high heat at the caliper, the fluid does get degraded and burnt. The very dark color of the fluid from the caliper, when you start the flush, is actually bits of carbon from the burnt fluid. Those particles, over time, can gunk up the seal areas of the slave cylinder. So, it is quite important to flush all of this stuff out on regular basis!
 

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Discussion Starter #20
OK. OK. Enough already;) I will perform a brake fluid flush ASAP. Thanks, PadG for the link to brake fluid flushing. The brake pads are still v. good so I’ll leave those for another time. Is the recommendation for Dot 5.1 agreed by all? Or do I use the Dot 4?
 
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