wajoshg Posted February 3, 2021 Report Share Posted February 3, 2021 Now then all, new to the forum so apologies if this has already been covered. I am having a pretty specific issue with my rear brake (98 Cota). It bleeds up fine, pistons move ok, and push out no problem, and there's no fluid leak. However, when in use, the pistons push out no problem until the pads contact the disc (brand new disc+pads), and then when any more pressure is applied the system seems to 'jam'. Essentially, the pedal feel goes dead firm, and even when standing with all my weight on the pedal, I only get a small amount of pad movement which is enough to contact the disc, but not lock the wheel or give any major brake force. I can only think that something in the master cyclinder is jamming or moving when under a certain amount of load. Frustratingly it doesn't look like there is any stock left of the OG master cyclinders, and Brembo UK just told me to go to Honda and wouldn't let me order. I'm running out of ideas and options, if anyone has any insight, or even a 2nd hand MC lying around, I'd be massively grateful. Cheers Josh Quote Link to comment Share on other sites More sharing options...
jonboy883 Posted February 3, 2021 Report Share Posted February 3, 2021 I had a similar issue on an Aptilia TXR where the rear calliper had been rebuilt and the previous owner had put the Pistons in the wrong way round. Are yours in the right way, if not the large flat surface cannot get the fluid pressure acting on it to move rhe piston out to apply pressure to the pads. Give it a check, at the very least! Quote Link to comment Share on other sites More sharing options...
wajoshg Posted February 3, 2021 Author Report Share Posted February 3, 2021 Cheers for the response @jonboy883 I can’t 100% say their in the correct way as never had them fully popped out the calliper. However my old mans owned the bike since 2000 and the brake has been spot on until last month, so I don’t think that’d be it. Appreciate the help though. Quote Link to comment Share on other sites More sharing options...
jimmyl Posted February 3, 2021 Report Share Posted February 3, 2021 Is it just since you changed the pads or before. Is the calliper twisted on the spindle he so the pads are contacting at an angle and jamming the pistons Quote Link to comment Share on other sites More sharing options...
jimmyl Posted February 3, 2021 Report Share Posted February 3, 2021 The 4rt master cyl maybe the same as 315 Quote Link to comment Share on other sites More sharing options...
wajoshg Posted February 4, 2021 Author Report Share Posted February 4, 2021 Hi @jimmyl No it was prior to pad change and was actually mid trial it went. Good thought re the twist but sadly all good, they’re pushing out even and (just) contacting at the same time. Quote Link to comment Share on other sites More sharing options...
jonboy883 Posted February 4, 2021 Report Share Posted February 4, 2021 (edited) Sounds like a master cylinder seal, as the pressure builds the fluid is pushing past an iffy seal internally and going from one side of the piston to the other. Do you need a new master cylinder or just a seal kit? Edited February 4, 2021 by jonboy883 Quote Link to comment Share on other sites More sharing options...
wajoshg Posted February 4, 2021 Author Report Share Posted February 4, 2021 (edited) @jonboy883 Yeah I did think that, just pulling fluid from one side of a seal to another, and then back again once lever is released. I’d prefer a whole new MC on the basis it’s over 20 years old and I think taking it apart might open another can of worms. However, given they appear to be like hens teeth I’d take a seal kit. I maybe wrong but it’s my understanding a 4rt one won’t fit as the pre 2000 Costa’s used diff brakes. It’s a Brembo rear I believe. Edited February 4, 2021 by wajoshg Quote Link to comment Share on other sites More sharing options...
jimmyl Posted February 4, 2021 Report Share Posted February 4, 2021 think it was just the rear caliper that changed - think master cylinders are all the same Quote Link to comment Share on other sites More sharing options...
rotors7 Posted February 5, 2021 Report Share Posted February 5, 2021 I managed to get the later rear brake caliper onto my '99 315. It's a while ago now but I think I only had to file a bit off the built in axle spacer. A few careful measurements did the trick. Quote Link to comment Share on other sites More sharing options...
jimmyl Posted February 5, 2021 Report Share Posted February 5, 2021 6 hours ago, rotors7 said: I managed to get the later rear brake caliper onto my '99 315. It's a while ago now but I think I only had to file a bit off the built in axle spacer. A few careful measurements did the trick. I'm sure the hub is narrower as well - had to machine my spare wheel when I changed to the newer model Quote Link to comment Share on other sites More sharing options...
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