When you want to post disposal of Fixed Assets, you can do it using FA G/L Journals. You must choose Disposal as FA Posting Type. In my examples, I post this journals with marked Depr. until FA Posting Date field.
You can get two different types of G/L entries, depends of setup in Depreciation Book. You can choose Net or Gross method on Disposal Calculation Method field.
In my first example, I have used net method. In this example I used FA with already posted some depreciation and write-down entries.
In my second example, I have used gross method. In this example I used FA with already posted some depreciation and appreciation entries (entries can be different, depends your FA has had appreciation or write-down).
All of these posting results depend only of FA Posting Type.