Had a weird experience today - a buddy asked me to refresh the rear brakes on his 2002 Ducati 998. New pads and fluid, no big deal. He brought the bike and the parts along. He bought a new sealed bottle of Motul DOT 5.1 fluid (I assumed he had the right stuff from his dealer), and after changing the pads I started flushing the rear line. After pumping maybe 1/2 oz of fluid things got weird. The action on the brake lever got real funky and it looked like gelled slime coming out of the bleeder. Color was normal but cloudy. I got worried real fast and checked the reservoir cap - DOT 4. He thinks the bike still had the original fluid so I was concerned it was an issue mixing DOT 5.1 and 4. But I think it's not a huge deal mixing those 3, 4 or 5.1 since they are all glycol based. DOT 5 is silicone based so you don't want to mix that. I mixed a little of the DOT 4 from the bike and some 5.1 in a bowl just to see what happened and it got a little slimy and snotty. Weird. Well, at this point it was either keep going and see what happened or tear the caliper and master cylinder apart. The brake lever didn't want to pump any fluid thru the line at all, and I though it was totally plugged up. We sucked hard with the Mity Vac and kept pumping, eventually stuff started flowing and the chunks stopped. I think we flushed almost the whole bottle of new fluid through, and things were feeling real good. Fluid was flowing nice and free, the color was good and the lever was nice and solid. I've bled a lot of brakes and never seen gelled fluid like that. He bought the bike new in '02, it is ridden fairly regularly and in good condition, other than probably never changing the fluid in the rear. There's really no chance of oil or anything else contaminating the system. Was it just age of the fluid? Was the fluid full of water? Was it due to mixing DOT 4 and 5.1 after all?
18 years is a long time for brake fluid to not have absorbed water. I'm bettin' water. That whole snot look sounds just like water in oil but, because oil gets churned up, water in oil looks milky. Don't expect great results from your handy-work, neither. Something about that master being bolted to the engine case. You can bleed it on a bench and get good pressure at the pedal, but once the engine gets hot you can kiss that pedal pressure good-bye. Might be okay for goin' to the coffee shop in town, but don't rely on it being there when strafing the twisties and you come to a downhill goin' into a switchback.
Just because DOT4 and DO5.1 are compatible doesn't mean that the brake system is 5.1 compatible. Just a wild ass guess tho. What you're describing is exactly what happens when you mix DOT4 and DOT5.
The heat transmits through the mounting bolts. What's needed is an alternative mounting point. On the rearset like everyone could be a cure if the exhaust wasn't in the way. Beauty has its compromises.
