I am quite busy right now, but I can fix/will be able to fix your car on Friday.
I don't have any tools I need, but the new ones will arrive in two days. Therefore, I’ll be able to fix your car on Friday.
I think when talking about the available timeslots (schedule) for doing something, we can use either "can" or "will be able to" to refer to future events; on the other hand, if it's talking about future ability (tools, parts, staffers, etc), "will be able to" is better.
Is my analysis correct?