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Discussion Starter #1 (Edited)
Fluid exchange on the 2006 K1200S ABS Brake Servo

Hope to share my thoughts about my recent experience with flushing the fluid from the ABS Brake servo in my 2006 K1200S. The old fluid I removed was brown and saturated with rust particles. (New fluid is nearly clear). I had never opened the brake system since I bought the bike new, but moisture gets in there somehow.

I was at 35000 Miles and went for another front tire change. BMW dealer told me that the front brake pads were at minimum thickness and recommended changing the pads. They also said that I needed to flush the ABS Brake Servo. It was then that the service rep told me that since I had not flushed the servo every 2 years (for $250), that there was a 40-50 percent chance that the servo would fail shortly after flushing the fluid.

Service rep told me the replacement servo would be $1800, plus installation. He also said that the dealer was working with a local vendor that would provide the dealer with rebuilt servos for around $600. Dealer suggested that I delay flushing the fluid until the rebuilt servo became available.

I spoke with one of the techs and he told me that the flushing procedures require the tech to open the ports from the brake handle and foot brake and pump new fluid through the input side of the servo, and then to open the bleeder valves at the wheel cylinders, and then use the pump in the servo to pump out the old fluid and replace it with new fluid.

Now I must admit that I am not a professional mechanic, but I learned years ago that when you bleed the brakes on a car that you put a 2x4 behind the brake pedal so you do not allow the brake pedal to go to the floor. The piston in the master cylinder normally only moves a limited amount because the pressure in the brake system limits its movement. This cause this area that the piston moves to be free of corrosion, but the rest of the system to have corrosion. If the piston seals run across the corroded areas that the piston normally cant go when the bleeder valve is closed, the seals get destroyed by the corrosion, and then you need to replace the master brake cylinder.

With that in mind I decided to exchange the fluid myself, but without running the ABS pumps in the servo. Using a vacuum brake bleeder, I vacuum bled the side of the servo from the hand and foot brake. There are three bleeder valves per brake system and all three need to be flushed until you get clean brake fluid out.

Then using a standard funnel ($1.99) (and not the $45.00 BMW funnel) and my wife to hold the funnel (dinner at Outback's when I finished) I vacuum bled the wheel circuits until the only thing that came out was clear brake fluid.

Since I did not run the pumps in the wheel circuits or use the hand or foot brake, I avoided any possible damage to the seals and the systems seems to be working perfectly well. Maybe I beat the odds and would have had one of the 50% of the brake systems that continued to work after the dealer flushed the fluids. Who knows, but I like the odds better if I vacuum bleed the system rather than relying on BMW procedures which very likely would have damaged the system.

Hope this help or is food for thought as you decide what to do with your brake system.

Lastly, the dealer told me that BMW changed the system in 2007 to a system less prone to failure.
 

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Yes, BMW changed the ABS in 2007, so now instead of the pump failing the electric power circuits on the PCB fail.

Thanks for a nice write up.
 
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