A common problem with FJ front brake calipers is pistons seizing. The cause is corrosion behind the seals which causes the seal to grip the piston and not allowing the piston to return.
The pistons should be easily pushed in with your fingers. If you find this is not the case then the answer is to strip the caliper down.
 
You must replace seals if the caliper is dismantled.
 
Pistons available (please note listing is for ONE piston and seals required for that piston): 
 
Front FJ1100 and FJ1200 1TX: To completely rebuild both calipers you will need to order 4 pistons.
 
Front FJ 1200 3CV and FJ1200 3XW:  To completely rebuild both calipers you will need to order 8 pistons. 
 
All FJ Models rear: to completely rebuild caliper you will need to order 2 pistons.
 
ALL PISTONS ARE PRICED SINGLY AND INCLUDE THE SEALS REQUIRED FOR THAT ONE PISTON