When I have a clip that's trimmed in AE, I still see the front and back of the clip in the timeline but it's opaque. The problem I'm having is when I want to pre-comp the clip, it brings the entire clip into the pre-comp instead of just the trimmed part. This is very annoying. How can I fix this?
I think you don't have the correct understanding of Precompsitions. If you precompose any layer, It will take the duration of the Comp no matter how long or short it is.
So to make a precomp with the length of trimmed area, you have to trim the Work Area first using B and N keys to set in and out point respectively and the context click on Time Ruler and choose Trim Comp to Work Area. Now bring this comp in another comp.
See the image below:
3D and Motion Graphics Artist