Rear brake binding and locking wheel

[chris-seed]

Hi Guys,

I recently installed a new rear brake master cylinder on my 1989 FZR. I went for a Brembo master cylinder from an R6.

When trying to bleed the rear brake I broke one bleed nipple from the original calliper, as it was rusted tight! So i replaced the calliper with one from eBay that cost £40 (around $50-$60). So I fitted this one and after bleeding the whole system using the Wiki article about how to bleed a dry brake system I tested the bike.

After riding for a minute or two and using the rear brake a lot the pads started to bind on the disc and it all eventually got very hot until it all started smoking and the rear wheel binded!! Quite a scary experience!

Since then, I have split the calliper and push back the pistons. They seem to be free enough and I've re-greased them. When I put everything back together and bled the system again it's still binding the rear wheel. Once it fully locks when I'm riding I have to get off, disconnect the brake lever and calliper and move the calliper around a bit until it frees up.

Not sure if there's something that I've done wrong or if one part in the new system is broken. Here's a breakdown of the components:

Master cylinder - I've taken this apart and cleaned it. It's got the threaded bar from the original FZR master cylinder attached to it, as the R6 bar was very short.

Hoses - Has a brand new Hel braided hose.

Calliper - FZR600 calliper - One thing I noticed was that the pistons on this calliper move together. So when I push in one piston the other one pops outwards (when the calliper is together and filled with brake fluid.

Any help would be great. I've ridden it 3 times now and it's binded the rear wheel on each occasion.

[M in KC]

There should be a tiny bleed back hole in the master cylinder reservoir to allow the brake fluid to return to the MC and ease the hydraulic pressure on the pads once braking is no longer called for. If that tiny hole is blocked or obstructed it can contribute to the symptoms you are experiencing.

[chris-seed]

Ah right. Yes I did see that when I stripped the master cylinder. I'll try cleaning that out and see what happens.

Thanks for that.