Brembo Rear Caliper

[mav617]

Hi all,

when I acquired my SZR it was pretty obvious that the rear caliper was totally stuffed, it leaked fluid and the pistons were seized. I therefore bought a secondhand same model Brembo off a scrapped Ducati which seemed fine. I fitted it recently, added a braided stainless hose and bled the system - which took ferkin ages, until I had good pressure at the pedal. However after a good blast I noticed there was increasing travel and a growing lack of braking power, so on return I bled it again but the same thing has happened again. Pads are fine, so I'm wondering if I have shot seals either in the caliper or the master cylinder. Operating the lever I can hear a faint squishing sound from the master cylinder. The system doesn't seem to lose any fluid, but on each bleed the fluid seems to be full of tiny bubbles. Any suggestions - short of replacing the caliper or the master cylinder?

[Jez F]

If its a Brembo master cylinder you can get a seal kit from Motomecca, had the same thing happen on my Guzzi a few years back.

[mav617]

Thanks Jez, have emailed them for details on overhaul kit for the M/C. I'm wondering now if the issue is with the braided line connectors, as one end is a normal banjo type fitting and one is a threaded insert (Melvin hose from Wemoto). The threaded insert I've fitted at the caliper with a banjo bolt at the master cylinder, but there's around 4mm of thread left proud on the insert at the caliper - I may put the rubber hose back on with banjos both ends and see if it's any better....

[MrFluffy]

Either air is getting in at one of the banjos or the caliper seals are leaking in which case you will see fluid coming out when you push the pedal and itll be obvious its happening by the pool of brake fluid that forms, or the master cylinder seals are gone or somethings amiss internally..
I had a rear brake on another bike that did this, bled up, braided hoses, brake like a rock, couple of days and spongy brake again. Changed out the master cylinder for a spare and all is well again with the rest of the system remaining unchanged...

[bikeseamus]

Mav
          No question that a squishing sound in the master tells you the seals are shot or there is a piece of old effluvia keeping the seals from sealing... or...curse the thought... the bore in the master cylinder is shot...corroded or scarred... that is rare, but sitting for a long time with water and air inside them can do it.

   Also, keep in mind that a non braided steel rear brake line will have a tendency to purge bubbles better than a more rigid kevlar or stainless unit will.  The rubber expands a bit and acts like a pressure spring.

  Examine the bore of the master cylinder you are about to rebuild to assure yourself the bore is not the problem, otherwise you will be wasting your money and time and will have solved nothing.  Kindly don't ask me how I learned that. Thanks.

[mav617]

Well, stripping everything out today and cleaning it all off reveals a small amount of fluid on the pistons - looks like the caliper seals are shot as suggested. Do I try and get new seals or look for a good secondhand caliper - this mightbe the lazy option but I could end up in the same boat. A mate has an air line, so if I cna find new seals I may try and replace them, and do the master cylinder ones at the same time.

Thanks guys for your help as always.

[guest27]

How do you know if the back brake is not working - I thought they were for decoration only... <grin>

R

[mav617]

How do you know if the back brake is not working - I thought they were for decoration only... <grin>

R

Agreed, but the pernickety MOT man will no doubt insist that it's functional as well as aesthetically pleasing...

[mav617]

Sorted, new seals in caliper and for good measure I bought a new master cylinder, as they're only £20 new from PDQ. original rubber hose is back on whilst I await a new rear braided hose from Wemoto - who originally suppled a front by mistake but have suggested I keep this and they'll send a new rear at their cost, nice one Chung. Having got so used to not using it, it took me ten minutes riding to remember to test it! Worked fine, then I don't think I used it again all day.....