Is final -l becoming a vowel?

Solution 1:

The sound you have identified is sometimes called "dark l". It is represented by /ɫ/.

control - /kənˈtɹəʊɫ/

wall - /wɔːɫ/

Some accents contrast an "l" at the start of a syllable with an "l" at the end of a syllable.

In the chorus of Another Brick in the Wall, Part 2, there are several examples of both kinds of "l":

We don't need no education
We don't need no thought control
No dark sarcasm in the classroom
Teachers leave them kids alone
Hey! Teacher! Leave us kids alone!

All in all, you're just another brick in the wall
All in all, you're just another brick in the wall

Here's the pronunciation of all the words with "l" in them, using Received Pronunciation as it's the closest to what the kids are singing:

control - /kənˈtɹəʊɫ/ (final)

classroom - /ˈklɑːsɹʊm/ (initial)

leave - /liːv/ (initial)

alone - /əˈləʊn/ (initial)

All in all - /ˈɔːlɪn.ˈɔːɫ/ (initial, then final)

wall - /wɔːɫ/ (final)

These are all easy to analyse except "all in all" which appears on the surface to be two isolated instances of "all", therefore both final. However, "all in" is pronounced as a single word, and is separated into syllables as /ˈɔːlɪn/, not /ɔːɫˈɪn/.

/w/, /j/, etc. are semi-vowels, and in this accent so is /ɫ/. So, not actually a vowel, but certainly with vowel-like qualities.