BRAKE FLUID FLUSH:
First lets discuss what we're trying to achieve.
Part of the regular service for the R1200R is a biennual (every 2 years) brake fluid FLUSH. A flush is different in some ways from a brake-fluid bleed, in that there should be no air introduced into the system when doing a "flush". Bleeding brakes is the process of getting any air trapped in the system (after opening the system for some repair) out. Flushing is getting old fluid out, and replacing it with new without getting air into the system.
Why do we need to do this?
Brake fluid is hygroscopic - ie - it absorbs and traps water. As the fluid ages, the fluid becomes contaminated more and more with absorbed moisture. The water is a bad thing in brake fluid. It has two undesirable properties:
- It lowers the boiling point of the brake fluid. Fresh brake fluid has a boiling point of well over 400F - so even if your brakes get quite hot, the fluid doesn't turn to vapor. If it did turn to vapor - it's easily compressible and you'd have no brakes. Once the fluid starts absorbing moisture the boiling point of the brake fluid starts dropping. Given enough moisture in the system - it could lower the boiling point to where it becomes dangerous.
- It causes corrosion of the brake components. Since dissimilar metals are used through the brake system - any moisture in contact with them will cause electrolysis - ie - corrosion of the parts. The corrosion can cause sticking of the brake components, causing brake failure.
Why doesn't my car call for doing this?
Because you don't own a BMW car. BMW cars have called for 2 year flushes about forever. Most car makers don't - counting on the greater volume of fluid in an automotive brake system to get the car out of warranty without a brake failure. Bad on them. ALL cars should receive a 2 year flush.
Why don't I just use DOT5 (silicone) fluid and be done with it?
DOT5 is not recommended or approved for use in ABS equipped brake systems. It has poorer lubrication properties than standard glycol based brake fluids, and the ABS modulator may not work correctly with it. I know someone is going to PM me with a message telling me that they used DOT5 for the past century in their ABS equipped bike and it works fine.. well - here is my reply - Good for you. Please DO NOT follow me when riding. At least not closer than a mile or so. I'll continue following BMWs recommendations.
OK - So what fluid should I use?
BMW recommends using DOT4. I see no reason to recommend anything else.
There are some high-performance versions of DOT4 available, and there is a DOT5.1 - which IS compatible with ABS systems and DOT4 fluid - but neither mean you can skip doing the binennial flush. It also was brought to my attention that some auto stores don't carry fluid labeled "DOT4" - they only have fluid labeled "DOT3/DOT4". This fluid is OK to use - the label means the fluid meets the specifications of DOT3 and DOT4, which makes sense since DOT3 has slightly lower standards for boiling point, and wet-boiling point than DOT4 has. Other than that - the two standards are basically the same.Is there any better DOT4?
As mentioned - there are some performance DOT4 fluids - which start with a higher boiling point. Ford made a DOT4 with some excellent characteristics (due to them putting undersized brakes on one of their trucks - which really heated up the fluid) - a Google will probably turn it up. I use Valvoline DOT4. It's cheap, and easy to find (any auto parts store.) BMW sells an expensive DOT4 - but it's always been "dark" looking right out of the bottle, which is typically a sign of water absorption - and that worried me, so it was back to Valvoline.
Note that most manufacturers do not recommend using fluid from opened bottles of brake fluid. They feel once opened, the fluid has started to deteriorate and absorb moisture. Since I buy fluid by the quart - there is no reason to skimp on the amount flushed through the system.
When should the flush be done?
BMW calls for the first flush to be done 2 years from the manufacturing date of the bike (and you can look that up using your VIN at www.realoem.com), and then every 2 years.
Are there any "gotcha's" in this process?
Sure - there are always opportunities for mistakes. Over tightening bleed nipples can be an expensive experience (best avoided by using the right length wrench and two fingers when tightening), spilling brake fluid on paintwork can make a nasty mess. Your best bet is to be careful with what you're doing, cover any exposed paintwork and read the instructions twice. Once to see what I missed (and letting me know) and once to make sure you understand them.
Yeah - I'll very briefly discuss replacing the stock bleed nipples with "SpeedBleeders." The cost is about $7/caliper, and these makes it much easier to flush or bleed the brake systems. http://www.speedbleeder.com/
WARNING: Brake fluid attacks paint. Depending on the type of paint - the attack can be very fast, or relatively slow - but your goal in doing this job is to avoid getting brake fluid on any paint. IF you do get fluid on painted parts - a rinse with soapy water is a very good thing to do - as soon as you can. If you delay too long you'll be washing the paint off along with the fluid.