One of my pistons in my 4 pot front calipers wont push in ?
Need to know what to do as i am trying to put new pads on
nick

 

you need to bleed off the brake fluid from the caliper nipple as you push the pistons back. collect whatever fluid is bled off in a clean jam jar and recycle back into the master cyl. reservoir.

 

personally, I would NEVER reuse old brake fluid - there's always a chance there could be bubbles and/or crap in there as well as the fluid being hygroscopic (attracts water) I recently changed the pads and discs on my my94 classic and my advice would be remove the cap from your fluid reservoir before you try to push your pistons back in, normally the whole system is under pressure so if you try to push your pistons in with the cap in place you're trying to push against that pressure - you'll also find that because your new pads are thicker than your worn ones, your pistons will sit further back and the fluid in your reservoir will rise so there's a good chance that you may have to remove some fluid from the reservoir in any case.

just my tuppence worth ................

 

no matter what you shoud remove the lid from the res or you can pop the seals, pushing pressure back up with no were for it to go..... and NEVER put it back in.... Use some fresh.. if only one wont go back in i sugest that u need to strip the caliper as its sticking