2006 CG125 Front disc brake

[knapdog]

The front brake is binding such that the wheel won't even free spin. I've taken the caliper off and the pads are OK but I'll replace them anyway and would appreciate if you could recommend any replacement makes. I've pulled the brake lever a few times to get some of the piston in view just so I could give it a bit of a smear with brake fluid to lubricate it a little but it would not initially go back in. Apparently this should happen just with finger pressure but I had to use a G clamp to force it back. A new piston and seal will cost about £20 if you think that may be the answer, whilst a new caliper is about £160.
Has anybody ever had this problem and d! Do you think a new piston will solve it ( plus, is it going to be a difficult job)?
The bike has done 10,000 miles

[barker]

has the bike been standing for any amout of time

[Alan CF]

sounds like you have a issue with the seal,
the seal it supposed to let the piston come back a touch when you let go of the brake lever,
there is pos corrosion behind your seal,
you will have to strip the calliper down and remove the piston, then remove the large O ring seal, there you will find your trouble,
clean the seal groove out and replace the seal... and it will work ok,
you might get away with using the old seal if ok, and not being that old,

what is happening is the corrosion is pushing the seal on to the piston and not letting it return.

[Jon]

The front brake is binding such that the wheel won't even free spin. I've taken the caliper off and the pads are OK but I'll replace them anyway and would appreciate if you could recommend any replacement makes. I've pulled the brake lever a few times to get some of the piston in view just so I could give it a bit of a smear with brake fluid to lubricate it a little but it would not initially go back in. Apparently this should happen just with finger pressure but I had to use a G clamp to force it back. A new piston and seal will cost about £20 if you think that may be the answer, whilst a new caliper is about £160.
Has anybody ever had this problem and d! Do you think a new piston will solve it ( plus, is it going to be a difficult job)?
The bike has done 10,000 miles

When my W650 calliper turned out to be pretty knackered I used the pad part numbers to work out what other bikes used the same caliper then bought a pair off a 500 kawasaki, used the right one that I needed and sold the other. Callipers for a 500 Kwak were a lot cheaper than the ones for the W650!

However, what has probably happened is that your piston has got corrosion and/or a build-up of old brake dust on it which is making it bind. I expect the seals are also a bit iffy too.

The seal kits are not cheap and there's no guarantee the repair will work if the piston is corroded anyway. Find the part number for the brake pads ( SFA054 ). Find other bikes that use the same pads and therefore the same calliper. Make a list of all of them and look on eBay for a used, good calliper from a newer crashed bike that's on the list....check the picture to be sure but it'll probably be exactly the same because the brakes are made by companies like Nissin, not by the bike maker and are used on many models and even different brands!

[wightegi]

EBC organic brake pads work well on the cg .

[knapdog]

A new piston and seal will come to £22.50 inc p.p. I think I'll go ahead and buy it.
Will pulling the brake lever force the piston right out to remove and will there be brake fluid everywhere?

[Bogger]

Yes fluid will go everywhere unless you bleed the system dry first, which is what I would suggest.

Bogger

[Alan CF]

but before you drain her pump the piston out as far as you can first.

[knapdog]

Right then boys and girls, who's going to tell me how to drain, fill and bleed the system?

[Boo]

In my experience the piston will be probably fine. The corrosion will be on the caliper itself, in the square section groove that the seal sits in, squashing the seal and causing it to function incorrectly (as Alan says it's designed to retract the piston from the pads slightly when you let go of the lever) .
Dismantle it and scrape any fluffy corrosion (probably jelly-looking mixed with brake fluid) out of this groove 'til it's spotless and reassemble with fresh brake fluid.
You may be able to reuse the seal if you are careful removing it, but might as well get a new one if it's cheap.
You shouldn't need a new piston.
How to bleed brakes is readily available info all over the interweb.