Default SD-Card issues with downloads (steam,jdownloader)

Hey, I've got a 32 GB class 10SD card in my V8P and when I try to download/install something via steam for example to the sd-card it start with decent 2MB/s but as it goes to ~50-80MB downloaded it's always the same:
harddrive is busy -> wait 5 minutes -> download more 10MB -> more waitings

so I never really finished a download from steam (like civ5), because even an hour of waiting it just maybe got ~200MB downloaded