Rear Brake Caliper Overhaul - Alternative Piston Removal Methods?

I bought the Rear Brake Caliper Repair Kit, from Wemoto in the UK, which I may be receiving tomorrow but I'm still hoping to not use it if the problem I now have lies elsewhere.

Note: My brakes are de-linked.

I have installed a CBR600F4i Rear Master Cylinder and it appears I have all the air out of the lines but I'm not getting any grip of the disc by the pads. I can push the pedal all the way down but the pads aren't gripping the disc.

It appears that the caliper is now looser on the disc too.

I did lower the pedal height slightly. Should I reverse the change?

I left a weight hanging from the pedal overnight hoping for a similar result as when I used a strong rubber band to keep the front brake lever compressed overnight which helped to bring the pressure up.

Prior to all my recent maintenance, the bike has not been ridden for 15 to 16 years.

Although the bike has not always been inside, I have always used a Bike Cover on it (Nelson Rigg). However, with the Rear Caliper being positioned so low, is it more vulnerable to the weather?

If the pistons are stuck and I can't loosen them by application of the pedal, how can I extract them to replace the seals?

I need Home Mechanic ideas firstly.

Thanks!!

 

There is no way (well... EXTEMELY unlikely) the pistons are stuck so bad in the caliper that hydraulic pressure will not move them. You either still have air in the system or your master is not functioning properly. That caliper would have to look like it went down with the Titanic and recovered to sell on eBay for the pistons to not budge with a properly functioning brake circuit. And in that case your brake pedal wouldn't be moving at all now would it?

Has nothing to do with your pedal height unless you installed it so badly it's hitting something very soon and not moving thru it's full range.

 

Instead of having the pedal at the Upper Most height, I lowered it by one complete turn of the Brake Rod Joint that connects the Master Cylinder Piston to the Brake Lever.

When I checked the bleeding this morning, only two minuscule bubbles of air appeared from the Outer Bleed Nipple and only one from the Centre Bleed Nipple.

The only other thing I can think of regarding the bleeding is to do it with the caliper located in its correct position.

Given that the fluid is being pumped through the lines, does that eliminate the Master Cylinder as being the source of the problem?

On Page 15-40, the Service Manual indicates to "Coat the new dust seals with silicone grease.". If I can't find any Silicone Grease, what would would be a suitable substitute?

 

If your master is pumping it greatly reduces the chances of that being it. You likely have a big stubborn air bubble. "Bleeding" at the banjo bolts can help a lot, but it makes a mess. I would try bleeding at different angles, ideally with your caliper above the master and the bleed nipple the highest point, You can also tap the hose to help dislodge bubbles.

Sometimes bleeding sucks ass. Had to go over to my neighbor's last night to do his rear caliper. He was convinced the master was shot. Had the pistons moving in about 10 minutes by being methodical about my setup.

EDIT: regarding lube... just use a very slight application of brake fluid. Just want it slippery so the piston doesn't catch and roll a seal. The absolute best is Red Rubber Grease designed to be used in brake circuits.

 

What the Captain says....... myself, I'd hang the rear caliper at tail light height....... the caliper is "looser" likely because the pistons haven't pushed the pads yet.....

 

Could be the slider pins in the caliper are siezed. Will the caliper move from side to side and the rubber boots on the pins expand/compress ?

Or could it simply be the CBR master cylinder is not up to to pumping three pistons ??