BMW R1200RT/R1250RT Forum

Very concerned about brake failure. I recently rode down a steep mountain and while lightly applying the front brake, the lever slowly sank into the handlebar, eventually reaching the grip and providing no brake force. The brakes were not very hot and I was not riding fast, most of my riding was between 20-45 mph. Releasing and reapplying the brakes normally provided good, normal pressure at the lever. Sitting still with the engine on or off, I can apply either light of very firm pressure to the front brake lever and it never sinks. Riding on an empty level road with no vehicles, applying light pressure to the front brake lever it sinks to the handlebar within 10-15 seconds. Can the ABS unit cause this type of failure?

Sounds like you have air in the brakes. You need to bleed the brakes.
Tenequip

Thanks Tenequip,
It's very possible, I just bought the bike very recently and the previous owner had just replaced the front fluid judging by the color.

I find it puzzling that the lever is so firm and the brake action is strong otherwise with no sinking lever when going 80mph or pushing it in my garage. The ABS seems to work properly, I've locked up the front brake intentionally on dirt and it released and reapplied as needed.

I'll make sure to start with a proper flushing and report back. Getting ready to travel so the bike may sit for a month.

You could just try cable tying the front brake lever as far back to the bars as you can and leave it overnight.