6 pots - pushing new pistons in

[Dusty ST]

After having my suspicions confirmed by a small pool of brake fluid I decided to go the whole hog and replace the seals and pistons as there was some scuffing in the coating on a couple of pistons.
The new small pistons slid in nicely, but the big ones didn't want to go, I tried all sorts, making sure they were parallel with the bore etc but no go, no way.
I tried the pistons without seals and they slipped, in no problem, so I compared new and old seals which looked identical, tried pushing the old pistons back with the old seals and still no go...
I've got them back now with a little encouragement by squeezing them in a vice - obviously I protected everything with bits of ply.
Once initial resistance was over come the pistons pushed home nicely.
Is that normal? Last time I replaced the seals I don't recall not being able to push all the pistons home using only my fingers to squeeze them in.
Have I just got weaker over the last couple of years, or is my memory on the blink? 

[gsxbarmy]

I've had that happen a couple of times in the past to me @Dusty ST try for ages and then suddenly they slide in, I now always wipe a thin film of red rubber grease on the rubbers and use a finger to wipe some brake fluid around the bore and most of the time the pistons slip straight in, but there is always one, once in a while.......LOL

[Hooli]

Aye they can be a bugger. It's worth double checking there is no corrosion in the grove behind the seals when you're struggling, or it is with my brakes anyway as I always have to clean the grooves out when rebuilding the calipers.

[Dusty ST]

Ah OK thanks for the replys -very good to hear it's similar for others!
I gave the grooves a good clean, but there was some corrosion on the lower piston seal groove that I cleaned as best I could but it's left some pitting.
They're currently not bleeding, so I've taken the calliper off and hung it to try to get the air to the top... It's too cold out there to be doing much else!

[Hooli]

I leave the calipers on the bike, open both nipples, fill the reservoir and ignore it for an hour. Gravity does it's thing & then they should bleed as normal. You'll know it's worked cause the reservoir is nearly empty when you come back.

I used to suck it though or reverse fill with syringes, but gravity is easier & gives time for a cuppa.

[Eric GSX1400K3]

Coating the new seals with some red seal grease (compatible with brake fluid) helps.  Also smoothing the bores with some wet-n-dry 2400grit paper helps a lot, blow the whole lot out with compressed air.  And dont forget to remove the bleed nipple, the trapped air behind the last one can stop it going in nicely.