Working on an RS955i for a friend. Front brake fluid changed and bled on last service 1500 miles ago ( approx 2 months). Brake was sharp then but has gradually gone off until now the lever almost touches the bar. It's not soft so not likely to be air (how would that get in anyway?) so I was thinking leaking master cylinder seal but that would normally allow the lever to go slowly all the way back under steady pressure. Ideas anyone?
Bixer,
When I used to race cars, I got very particular about brakes.
What was the condition of the "new" fluid? Was it new to the bike or new from a brand new, sealed, metal container? Brake fluid is hydroscopic - that is: it very friendly to moisture. Problem is: the moisture isn't friendly to its performance. If it was installed from a container sitting on the shelf in the garage (that wasn't factory sealed metal container), there is a good chance water was introduced into the fluid. Water boils long before brake fluid and the result is the introduction of "air" into the system.
Second guess and less likely is that the brake compound was changed to an aggressive material that has eaten the rotor discs beyond their operational tolerances. Meaning, the pad material has worn away the disc material requiring a throw that exceeds the calipers operational specs.
Also be sure that the correct fluid was used. I haven't broken into my brakes yet, so ... I don't know which is required. But, the brake fluid must match the system specs or it can/will eat seals.
Unless the rotors appear substantially thin, I'd guess it need a bleed with new fluid.
Caliper not sliding freely?
Quote from: "Bixxer Bob"Working on an RS955i for a friend. Front brake fluid changed and bled on last service 1500 miles ago ( approx 2 months). Brake was sharp then but has gradually gone off until now the lever almost touches the bar. It's not soft so not likely to be air (how would that get in anyway?) so I was thinking leaking master cylinder seal but that would normally allow the lever to go slowly all the way back under steady pressure. Ideas anyone?
Got the same problem about to fit speed bleeders and new fluid. I find tieing the lever back to the bar over night which seems to sort things for a while cheers Spud :wink:
Check pad and disc thickness, if these are ok then there is a chance you still have some air in the system. Bike brakes can be a biatch to bleed due to the master cylinder being so small and only displacing a small amount of fluid. When bleeding I pump the brakes til hard then crack open the nipple whilst holding the pressure on til it has released then tighten the nipple again and repeat as many times as is necessary. Hope that makes sense.
Thanks for the ideas. I've already advised him to tie the lever back, and will run through the other bits as soon as I can. time to invest in a power bleeder aka Mustang I think.
has the bike got rubber or braided hoses? ABS or non-abs bike just a few ideas
I use a a syringe and tubing for bleeding brakes, and pull the fluid down from res to caliper and nipple. you will see the air bubbles getting smaller and smaller until just fluid appears in the syringe.
used this method on quite a few bikes, from ER5, DL650, TDM850, ZZR1100, and a few more.
do like dave b says but do it from the bottom up. ive never tried it but been told its a good way of bleedin
Hi,
just managed to get my brakes as good as new on my 1996 Steamer! I have never achieved a result as good as this ever before.
I removed the callipers one by one from the bike, still connected hydraulically, and rolled them around with the hollows of the pistons upwards allowing any bubbles to float out and to the back of the callipers and gave them a little shaking at the same time. Then I imagined the drillings and again rolled them around to move the bubbles into the drillings and up to the bleed point.
I then reattached them to the bike and bled them. I can honestly say that they are now as good as my new Tiger 800XC!!!
All these years I have f****d around and eventually got pretty good results and passing MOTs - but nothing as good as now.
I hope this works for others.
If it's anything like the Daytona...check the pistons. One or more may be stuck.