1. remove piston from piston cover
2. press apart reatiner remove pin from piston cover leave reatiner in cover
3. remove snap ring in brake band piston remove cup spring
4. Insert pin in brake band piston
5. slide cup spring over pin until spring rest on piston insert snap ring
6. press the assembled piston over the piston cover and push until the retainer snap on the pin

Do not move the cover so the parts slide apart and press the piston in to transmission just so the retainer ring just can be put in place.