Reading Mac OS Extended HDD via USB

Hi,

I have just upgraded my HDD in my 2010 27" iMac. I am wanting to copy the data from my old HDD to the new one in my iMac. Only problem is that i can't get OSX to mount my old HDD using my HDD docking station, though I can get it to mount but it is not readable when using a HDD enclosure (took apart an external HDD). My old HDD is formatted as Mac OS Extended (Journaled), and is a 3TB HDD.

Any help getting OSX to read my old HDD so i can copy the data across would be great.

I'd rather not take apart the iMac again, put the old HDD back in, copy off the data to an external HDD, then swap the HDD's again but that may be the only option.

Thanks,

Cameron.