Rear brake problem

[Giddsy]

Hi all,

I recently decided to do a rear brake caliper clean up / rebuild. The brake e=was working fine but just very, very dirty when I changed the pads and fluid had probably never been changed.

Anyway, I have now rebuilt it but the brakes are seriously binding. when I remove the caliber I can push one piston in easily and it has equal reaction of popping other one out and vice versa. It is very difficult to push them both in, i.e. the fluid doesn't seem to be returning up the line so to speak.

I did wonder that I had it empty of fluid for a few days as I got side tracked. Is it possible the lines have cracked or swelled in this time thus not allowing fluid to return into the system?

It comes out easy enough though if I release the bleed nipple.

Can't see how the MC would have failed in this time.

Any thoughts appreciated.

Thanks

[gt900uk]

What bike? SV's not all have single piston rears? Is it a sliding caliper if so its most likely jamming on the sliding pins if the pistons seem fine.

[Giddsy]

Its 2001 naked. Single piston so not sliding unfortunately...

[Giddsy]

Also I live in Australia and it's hot now. Think new lines will definitely be where I start..

[gt900uk]

OK you said above it had two pistons. The lines won't cause it to bind, either the piston isn't moving smoothly and is jamming or the sliding pins are jamming. Did you replace the piston seals when you rebuilt it?

[gt900uk]

Is it the front or the backs that are the issue? Thread title says one thing post could be an issue with the fronts.

[Giddsy]

OK sorry mate, and thanks for your patience. It is the rear brake. It has 2 pistons directly opposite each other. I said single as it is not 2 side by side as the front ones are.

Hope that makes sense.

Didn't replace seals as they seemed perfectly OK.

I don't think seals are the issue as each piston will move - just not independently...

[Bibio]

when you split the calliper to pull the pistons did you clean out the recesses that the seals fit into?

when you installed the pistons did you use Red Rubber Grease on the seals?

when you filled the system with brake fluid did you bleed both nipples (there is one on the back)?

another problem that curvy SV's have is air gets trapped at the MC so you have to crack the banjo while applying pressure and close before the pedal gets to max stroke (use a damp rag to catch the fluid).

have you stripped cleaned and greased the brake pedal pivot shaft?

[gt900uk]

Ahh ok apologies, that makes sense, the older sv must have different rear caliper to the newer ones then. If it was working fine prior to cleaning it is most likely something you have changed when servicing the calliper. How much force is required to move the pistons? I think it is still likely that it's something sticking so either a swollen/damaged seal or where the pads are attached and slide on the pins and springs. Did you pop the pistons out or just clean and push them back in? I guess it's not beyond possibility that the internal diameter ID the hose has collapsed in a manner that is stopping the pressure getting back out but unlikely I would imagine. You could loosen the banjo bolt and try pushing the pistons back together to see if it works with the hose effectively bypassed, just watch for the fluid leaking out. I would be tempted to get a rebuild kit and just change all the seals anyway.

[Giddsy]

Hmm.. Few pointers I could try there.

Yes to recesses, rubber grease.

I reverse bled with syringe from rear nipple but only bled conventional way from front.

Will try cracking banjo at mc. I take it that is what you mean? So kind of bleeding at mc?

Thanks

[Giddsy]

Oh and no to pedal but that seems very free moving but will check if other points don't succeed..

[Bibio]

yup bleed the MC.

the lever pivot points are know to bind up on the curvy's

if all that fails then its a MC rebuild as it could be jamming.

[Giddsy]

Tried everything twice - no joy. Mc rebuild kit in post.