Good evening,

I've just put back together the brake system on my CBR600F4, this included an entire rebuilding of the components, including: New master cylinder, new piston seals, polished pistons, new brake fluid and copper grease on everything.

The wheel spun freely until I applied the brakes at which point the pad pratically gripped the disc and would not let go. OK. Removed the pads and tried to free up the pistons. With a bit of movement I reintalled the pads and applied the brakes again, same thing, they bound to the disc.

I'm really stuck with this, although there are two possible causes I can think of.

Firstly, when I was getting the brakes diagnosed by a bike shop they clamped the braided hoses (Venhill custom length hoses), leaving a permanent mark in both of them. Could this effect the brake binding?

Second, the piston seals were a mixed bag (god know why I accepted them). Half were good quality branded seals which came in bags, the other half were odds (correct sizes) which I "cleaned" up and put in. I wonder if these would present themselves as an issue immediately?

Any help would be greatly appreciated as I'm now running out of time, money, patience and the will to live!

Many thanks

 

Have you bled the brakes again? Are you surer here is no air stuck in the master cylinder if you've rebuilt that recently?
Air stuck in a hydraulic system heats up when compressed and does exactly what's happening to your brake pistons.
If further bleeding doesn't help then try taking the callipers off , remove the pads and pump the pistons out slightly. Using a g clamp or similar wind the pistons back in and note if any of them feel stiffer than the others if you've got one sticking or perhaps even one in each calliper stiffer to move than the adjacent one then it suggests there's something wrong with the piston and/or seals.
You may decide at this point to strip the callipers down again and take another look at what you've done, condition of pistons and...... are the seals you've been given a) new and b) the correct size?
As for your hoses being kinked by the shop I think you should complain to them about that. What on earth were they thinking? A stupid mistake. You would not be taking the **** to ask for new ones.
Looks like you're going to need a bit more patience. Sorry.

 

Thanks for the reply Henry,

I'm going to do what you suggested and see if there is any obvious resistance from particular pistons. This gives me something to think about for awhile rather than rushing out to buy replacement parts!

As for the brake lines, it was a "side job" they done to help me diagnose the braking issues I had (judder under breaking). The mechanic ran the discs individually by clamping the opposite line to see if either disc was causing the judder. It seems terrible in retrospect, going to count my losses there as it was months ago and I have no proof/receipt they carried out the work. Ho hum!

I'll report back on how things go. Many thanks.

 

Your brake line is the problem. Rubber hoses can take being clamped if they are in good shape, but braided can't. The tube inside is not rubber and will remain restricted not letting the fluid return properly.

 

Totally agree with demon. If your seals were the problem, you'd have a nice messy puddle of evidence. Pinching a brake line (even if it's the stock lines) is NOT like pinching a fuel line...