Removing semi-seized brake pistons

The Other PaulG

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Evening all.

I am servicing a friend's T100 Bonnie and the rear caliper is in need of a lot of TLC.

So much so, that it was a struggle to even separate the caliper from its carrier. The pins had all manner of nastiness and corrosion (now fixed).

However, I am now at the stage where I need to remove the pistons.

Stupidly... can't believe I did this... I forgot to use the brake pedal to pump them out before disconnecting the brake hose and allowing a load of air into the system. :blast

They're pretty stuck - a gentle attempt with mole grips and inner-tube protection didn't shift them although they have moved maybe 2mm during my recent work.

They are currently swimming in brake cleaner fluid (inside and out) whilst I await a generous soul from this forum to tell me how I can get them out without re-connecting and bleeding the hydraulic system... :D

My immediate thought was to deploy the trusty heat gun but I don't want to trash the seals.

Any thoughts?
 
go buy seals and pistons , you cheapskate.

or reassemble , block in the middle , and compressed air to blow everything out .

carb https://www.fowlersparts.co.uk/parts/10052/bonneville-t100-carb-models/rear-brake-disc-and-caliper £67

efi https://www.fowlersparts.co.uk/parts/7706/bonneville-t100-efi-models/rear-brake-caliper-disc nla

or bolt it together bleed it up .

calipers are same part number !

https://www.ebay.co.uk/sch/i.html?_...e_name=powerhouseautomotiveltd&_bkw=seal+kits

https://www.ebay.co.uk/sch/i.html?_...powerhouseautomotiveltd&_oac=1&_nkw=t100 rear £58

buy the parts first , before you destroy everything
 
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Just seal one inlet and stick a grease nipple in the other and pump full of grease.
 
A foot pump and suitable needle / adaptor can sometimes work by giving a short sharp blast or building pressure over time

Coca-Cola can sometimes work to free stuck stuff if left overnight
 
try this
ttps://www.youtube.com/watch?v=zMCJSX3fW-g
 
go buy seals and pistons , you cheapskate.

....buy the parts first , before you destroy everything

Ha! OK I bought the seals!

Compressed air didn't shift them so I'll get back on it tomorrow. Right now hooking the brake line back on and bleeding them back up is looking like the easiest and safest option.
 
Buy a motorcycle brake piston removal tool kit , will remove any siezed caliper piston
 
Don't you love it when the good guys win....?

Important lesson learned, I was keen to make progress with this job but by going back a step and re-bleeding the system, the pistons came out like blokes at a Kylie concert.

All manner of nastiness and years of neglect - so everything's currently having an overnight soak in brake cleaner fluid, then when the new seals arrive they'll go back together with smears of red grease.
 

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Thanks for the collective thoughts on this - it'll perhaps help anyone who searches for similar in the future.

Completed the service, then took advantage of a very still and quiet morning today to take it for the post-service test ride. These are fun bikes on B roads, highly predictable and with enough 'go'. Its owned by my friend Bernie and she rides quite gently so I thought I'd better blow the cobwebs out over Chobham Common!

Pretty bike.
 

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