Elektron Musical Instruments

anyone have experience syncing md with 808
I try to slave 808
but it only play few notes then stop
if I press stop, 808 can play continously, but that is not right

when I master clock 808
it is fine, md will play and such
one thing, switching patterns on 808 with cymbol and non-cymbol 
patterns will cause 808 and md to messup the beats, then I have to 
stop

help