Hello all I am working on the MC28 in the garage and the rear calliper was seized the other day
So pulled it down given it a good clean greased it all up and put it back together
Pushed the brake peddle a few times to make it all meet up and “nut’s” it’s grabbed the disc and wont let go again.
So im fairly sure it’s down to the pistons. As they were a complete nightmare to push back “I say push as if it was easy” into the calliper.
So if I drop them out clean them up with sum emery. Will I need to replace the seals or is it a case of suck it and see?

dont use emery on the pistons. try some brake cleaner, you can get it from halfords etc.. if they're really cruddy use autosol or another mild abrasive. may well be worth getting new seals while you're at it.

best to pop the piston out, clean everything thoroughly. definately replace the fluid and dust seals, lubricate seals with some brake fluid before pushing piston back in, piston should be able to be pushed in by hand if everything is clean and assembled correctly.

cheers

richie.

I've cleaned pistons with wet and dry and not replaced seals more than once, not dead yet!
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Please do not PM me technical questions, if you can't find it on the Forum start a thread

When I said emery I meant a fine wet and dry
So out they come then
They are anything but easy to move at the moment.
Ill let you know what happens

that Sounds like a problem with the master cylinder to me

I have replaced many caliper seals on bikes and cars and the main reason for sticky pistons can be 2 things. A corroded piston causing it to be tight or corrosion inside the caliper behind the seals, The later being the most common. If the pistons look rust free pull them out and then carefully remove the seals with a blunt pick noting the way they came out then clean the groove they were sat in. The groove is what usually gets corroded which then causes the seals to pinch tight on the piston. Reassemble and hey presto as good as new. Inspect the seals before refitting them as they can sometimes start to split.

have you tried loosening the banjo bolt on the top of the caliper and seeing if it will push back then ?

First ride out, and within one mile both front & back brakes had seized.
Calipers off, inspected pistons, free as a bird. Checked master cylinder, problem with the piston valve, not allowing the brake fluid to bleed back through to the reservoir at the required rate, causing the brakes to stick on. Tallies with the fact that after the brakes had locked, a few minutes later they freed off by themselves. On stripping the cylinder, quite a bit of corrosion around the piston circlip, the dust cover had perished, the piston inner seal rubbers didn't look great, but not overly bad. Blowing through the cylinder, moving the piston in and out, certainly felt a restriction. Hoping a piston rebuild kit will do the trick. Keep you posted.
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Rich
MC21 Track Bike / RS250 NF5 'Spencer', NX5 'Cadalora' & NXA 'Aoyama' / RS500 / Two Brothers Racing RC30

If i,d paid that kind of money for a bike i'd want the shop to sort it
You should have some come back on the dealer you got it from.

o o


Last edited by DifferentStrokes on Mon Sep 28, 2009 6:53 pm; edited 1 time in total

The dealer is going to stand the price of the parts
I'd rather do the work myself however.
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Rich
MC21 Track Bike / RS250 NF5 'Spencer', NX5 'Cadalora' & NXA 'Aoyama' / RS500 / Two Brothers Racing RC30

Nice one mate! i was going to say if he didn't sort it i could have gone up and had a word with him with it only being less then a mile up the road from my place

Cheers Fenton, I'll remember that if I find any other porblems with the bike.
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Rich
MC21 Track Bike / RS250 NF5 'Spencer', NX5 'Cadalora' & NXA 'Aoyama' / RS500 / Two Brothers Racing RC30

caboking wrote:I have replaced many caliper seals on bikes and cars and the main reason for sticky pistons can be 2 things. A corroded piston causing it to be tight or corrosion inside the caliper behind the seals, The later being the most common. If the pistons look rust free pull them out and then carefully remove the seals with a blunt pick noting the way they came out then clean the groove they were sat in. The groove is what usually gets corroded which then causes the seals to pinch tight on the piston. Reassemble and hey presto as good as new. Inspect the seals before refitting them as they can sometimes start to split.

As mentioned above.
This was the main problem
Popped out the piston and seals and found a fair bit of corrosion and a tarry build up under the seal
All cleaned out and put back together now.
And it feels newer than a new thing.
Guess it’s not always good to not use your bike hey
Thanks for the help gents