Representation of Proto-Germanic /þ/ - /d/ vs. /t/

Not an active learner here, but just curious from a hobby linguist perspective - as a German native speaker, I noticed that the realisation of the Proto-Germanic /þ/ ("th") sound (which generally stayed that way in English and Icelandic but got shifted to /d/ in German and Dutch) seems to be quite random in Swedish, sometimes it's a /d/, sometimes a /t/

Examples (EN - DE - SV):

• thou - du - du
• that - das - det
• think - denken - tänka
• (dry¹⁾ - dürr - torr

(¹ has no direct equivalent cognate in modern English, but "thirst" is related indirectly)

So this makes me wonder - is the realisation of /þ/ completely random in Swedish or does it follow certain rules that I'm not aware of? Maybe it becomes /d/ just in pronouns and /t/ elsewhere?