Rear brake tight

[Hasujek]

Hi, I have recently changed my rear disc and pads on a CBR125 and have an issue with the brake. The issue is that somehow the brake is very tight, it slows the bike down whilst riding, like a little bit of pressure on the braking the whole time. It is really difficult to push the bike forward. When doing about 5-10mph you can hear the brakes scraping. When changing the pads I had an issue with putting the pistons all the way back, and ended up needing to re bleed the whole rear brake system. Can anyone suggest what to do before they f*up.

[RhynoCZ]

Did you clean the caliper pistons before you pushed them back in? Also, you say you had to bleed the system, but I'm going to ask anyway, are you sure there isn't too much of the brake fluid in the system?

If you didn't clean the pistons, then take the pads out, use the master cylinder to push the pistons out a bit and clean them. Use brake proper cleaners only! WD40 and other stuff swells the seals = no good.

Proper operation of the caliper: When you apply the brake and then let go of the pedal/lever, the pistons of your caliper should go out quite effortlessly and then as you release the brake pedal/lever they should go back in a bit. Take the caliper off, take the pads out and watch the pistons do the trick. If they don't go back again = dirt/crud ring on them keeps them from doing so.
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'87 Honda XBR 500, '96 Kawasaki ZX7R P1, '90 Honda CB-1, '88 Kawasaki GPz550, MZ 150 ETZ
'95 Mercedes-Benz w202 C200 CGI, '98 Mercedes-Benz w210 E200 Kompressor

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How much is a new rear caliper? You're going to either have to clean the piston/s and maybe change the dust and fluid seals, or replace the whole lot.

It sounds like it's binding. All the time your pads and disc are low, the piston/s are going further and further out of the caliper, revealing more clean piston. Now you've upped the pad and disc, the piston needed pushing back and now the part moving past the seals is already dirty and not returning properly.
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TZR250 2MA road, TZR250 1KT road, TZR250 2MA race, TDR250, YZF-750R Boost colours.
Jaguar S Type 3.0 V6 Sport R, VW Transporter T5 GP LWB Shuttle 140ps DSG.

[RhynoCZ]

I'm going to agree with mpd72, that replacing the caliper would be the easiest way, but I'd still encourage you to try fix the one you have, as it is a good exercise and it isn't that complicated, nor expensive.
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'87 Honda XBR 500, '96 Kawasaki ZX7R P1, '90 Honda CB-1, '88 Kawasaki GPz550, MZ 150 ETZ
'95 Mercedes-Benz w202 C200 CGI, '98 Mercedes-Benz w210 E200 Kompressor

[Courier265]

Common problem due to not cleaning the piston properly, first up spray the caliper with brake cleaner, allow to dry the pump the piston out and clean with a long piece of cloth and brake cleaner. Before pushing in the piston, drizzle some brake fluid around the seal and push piston in..

When replacing the hanger pin, make sure the hole in the brake pad is a good fit. If it's tight, enlarge the whole till the pin fits properly. Grease pin with normal grease and fit the pads.

Job done.