Have had a V4 PP for 18 months now and love it other than the top heavy feel under 5mph. However last weekend, I went for a brilliant ride with a mate then had to take the M40 back to meet a deadline (after losing track of the time) and got stuck in about 20 miles of tailback. So filtered through the whole line using the back brake to steady the bike a lot along the way. I can only assume that the temp of the brake fluid went right up as suddenly about a mile from the end of the queues the back brake totally failed. The brake pedal was totally soft with zero braking effect. After trying the back brake numerous times, I navigated the final mile just using the front brake. Bizarrely, once the traffic freed up I tried the back brake and it was fine. What’s all that about? A friend said he had the same experience on a triumph tiger and was told the ABS unit fails at high temps(!) Any insight or shared experiences and explanations welcome.
If you were dragging the back brake whilst filtering for that length of time the fluid likely got too hot and boiled. Fundamentally; in gas form it compresses, in liquid form it doesn't. This will mean the pedal will be soft. Once cooled back to liquid the firmness returns. Doing this repeatedly is going to probably deteriorate the fluid to the point that the back brake becomes effectively useless. Is the fluid in the reservoir still clear/light, or it more opaque/darker? If the latter it's time to change it. Not sure on the service recommendation for the V4 but for the 1260 it's every 24 months. Not sure what Ducati put in at the factory. Might be worth bleeding through, having syryinged almost of the old fluid from the reservoir, and replacing with Motul RBF600 fluid. High quality brake fluid will have a higher boiling point. Though in this case would probably still boil.
Thanks, the bit about the the fluid boiling to gas and compressing was what I'd missed. I used to use Motul RBF600 fluid on my 1200 and 1260 PP's as the back brakes were notorious for being poor. I've had no problems with the V4 before this experience.
I use the RBF 660 more road friendly from what I have been told , the 600 is more track and needs to be changed more often .
I believe 660 has a slightly higher dry boiling point than 600, but wet boiling points are the same for both of them, they’re both classified as racing brake fluid. IME, and I have used 660, on a variety of bikes where the rear brake pipe runs perilously close to the exhaust, it requires changing more frequently than Motul’s regular DOT4. It’s noticeable within the first 12 months how dark the fluid becomes as it absorbs moisture.
Thanks for the info , I do as a rule change all fluids once a year , for piece of mind. The 600 or the 660 will improve the brakes as they were perfect on the recent mountain tour. Just wished the tyres lasted that long lol.
It has a higher boiling point which was the factor that made me choose , plus input from JHP Racing .
