Very soft rear brake

[jasaretta]

Being the least mechanically minded here - I was wondering what could cause this. Rear brake has just gone very soft. Still works but I need to push much further. Fluid levels are ok.

Any ideas?

tia

James

[Speeddog]

Most likely, you need to bleed the system.

Alternatively, it's possible your master cylinder has gone bad.

[jasaretta]

Most likely, you need to bleed the system.

Alternatively, it's possible your master cylinder has gone bad.

Thanks - looks like a visit to the man that knows more than me

[Christian]

+1 on bleeding.

The S4RS has a rear brake caliper that is mounted upside-down and therefore, much like the 748/9XX bikes, it can be quite difficult to bleed properly. You may have heard people joke of the uselessness of the rear brake on Ducati bikes, and this is possibly the origin of the joke.

Bled properly it should be fine, but it may require occasional bleeding in the future to maintain the feel you're looking for.

[rockaduc]

I have to bleed the rear brake on my s2r 2x/yr on average.

[hypurone]

It is NOT normal to have to bleed a hydraulic system to remove air unless there is a defective component, period. If you have to bleed it (for air or an internal by-pass) there is something defective. In 20 years of certified automotive tech work, there was ALWAYS a bad component when there was air in the system or excessive travel (internal by-pass failure of the master or proportioning valve etc)

It IS normal to flush the system to improve the fluid quality and thereby firming up the pedal/lever. But this is usually to improve the feel, not eliminate the amount of travel it sounds like you are experiencing.

I have had my RS for a little over 2 years now and the ONLY time I needed to bleed it was when I installed the Sato's (which use a pressure switch for the brake light).

Let us know what your tech finds....

[rockaduc]

Hmmmm. Maybe I should check my MC.

[hypurone]

Hmmmm. Maybe I should check my MC.

I have also seen issues with the calipers where they bleed air in thru the piston seals or joint o-rings. You "usually" see signs of fluid seepage on the caliper side of things tho if those seals are bad but you could be the oddball too. Well, your bike I mean... 

[Speeddog]

I've seen a couple of the black master cylinders go bad.

I've seen quite a few of the S*R bikes with flabby rear brakes, and they respond to a thorough bleed.
Not sure why they seem to be more prone to issues. 

[madalf71]

Hi All.
S*R, make life less stressful,
Remove rear caliper when you bleed it,
And yes does come off without removing rear wheel.
Cheers.
Madalf

[RUFKM]

Diagnostics on any brake issues should start with cleaning. Don't judge, classify or categorize until they're clean. Use a Scotch Brite pad on the rotors like you mean it. I've seen threads on warped rotors and soft rears before. All of the symptoms described were ones I had but eliminated by simple cleaning. Do it everytime you wash the bike
(sorry MrIncredible there is some benefit to clean).