overhauling/cleaning brakes, should I replace piston seals?

[mr_magicfingers]

My 1150gs is 10 years old, done 78k miles and appears to have the original brake hoses on it. As part of my ongoing upgrade/preventative maintenance of the bike (only had it 6 months) I'm planning to replace the hoses with braided ones. I figured I'd give the brake calipers a good clean out when I do the hoses and get them working at their best. I've not stripped calipers before so I'm wondering if I should replace the piston seals while everything's apart?

I know I could wait until I pull it apart and look at the condition of them but, as I'll be doing it when I next have a spare weekend and, if I need them I won't be able to nip out and get a new set if I do, should I just order the new seals ahead of time and fit them?

Looking at the manual, it seems a straightforward job, except that it suggests using a compressed air gun to push the pistons out. I don't have one easily to hand and I'll have drained the system to get to that stage. Is there another way to get the pistons out or should I just pop them out before I drain the system by pumping the brake lever and then clean up the fluid afterwards?

Thanks,

Justin.

 

[Stewart H]

You will only get one piston out by pumping the lever, to get them all out you will need compressed air, the recommended method for cleaning them is to push the pistons most of the way out then clean what you can access, I have successfully stripped and cleaned calipers without resorting to new parts YMMV
Overhaul kits are quite expensive as they include new pistons.

Stewart

 

[Greg Masters]

Justin

BMW offer a seal and piston set. It's really worth fitting if you're overhauling the brakes.

My bike passed it's MoT but the brakes started dragging the very next day. A new piston/seal kit TRANSFORMED the braking performance.

If you're fitting new pistons, you can use cow-castrators to pull out the old pistons. Use the supplied grease when refitting. NB the pistons and seals are different sizes!!

Greg

 

[Timolgra]

You will only get one piston out by pumping the lever, to get them all out you will need compressed air,

Use a piece of wood to stop one piston just before it's out, pump the other out and i've found the other will then come out by hand on most bikes

 

[Hustler]

Use a piece of wood to stop one piston just before it's out, pump the other out and i've found the other will then come out by hand on most bikes

I've always got them out this way no problem.
A bit more class here though as I use a little clamp instead of a piece of wood.

 

[ELIMINATOR]

I would have thought that if the brakes are not having any problems a good cleaning would suffice, then use a thin smear of red rubber grease at the interface point between piston and caliper, to lessen the chance of any shite getting into the dust seal's groove.