Rear brake pistons not moving as they should

[SeanGSUK]

Rear brake pistons not moving as they should. I have replaced the pistons and seals, cleaned out all the channels, cleaned up the piston aperture and seal slots with emery cloth, rebuilt. Both the pistons move under pressure, but only a couple of mm. Not enough to grip the disk.
If I clamp either one of the pistons the opposite one still only moves the same distance, not double?
I thought there may be a air leak still so I submerged the caliper in water (don't worry it's hooked up to an off bike master cylinder and I will make sure it's totally dry before it goes on the bike), no leaks!
I replaced the rear master cylinder last year, is don't think it is that. Any ideas?

[Guest]

Air or one or one or both of the pistons are stuck. They should keep coming out of the caliper until they grip the rotor and then return.
Take off the caliper and pump the brakes and see which piston stops.

[Agemax]

did you use aftermarket or OEM suzuki seals?
some aftermarket seals have been known to be ever so slightly over sized, not allowing the piston to move with the deformation of the seal when pressure is applied.
were the pistons a very tight fit to get into the calipers?
if this is the case you need to remove the seals and gently rub down the outer circumference of the seal with some fine wet and dry.

or, you could go and buy original Suzuki seals.......

[londonboards]

Sean - if you get a chance pop along to the UK Social Group and drop your name in there.

Hoping one day some of us might meet up or go to a show together.

Greetings

[SeanGSUK]

I did use pattern seals, but having had trouble before I did rub them down a bit. Pistons were fairly easy to get in. I will pop them out again and rub them down a bit more. Maybe they were not smooth enough after my first rub down.
thanks for replies.