American English Phonetics

12.3.3 Pre-l Breaking

In Ga, vowels before [ɫ] tend to be diphthongized, so you get a centering offglide between the vowel and [ɫ], which is particularly noticeable afte close (free) vowels and closing diphthongs, as in feel [fiːəɫ], rule [ruːəɫ], foul [faʊəɫ].

The rule can be formalized as follows:

Pre-l Breaking: Insert a schwa between a close tense vowel and a coda-final /l/.

Sometimes pre-l breaking applies before ambisyllabic /l/, but when preceded by /iː/ or /eɪ/, as in feeling, feel it, failing [ˈfiːəɫiŋ, ˈfiːəɫ ɪt, ˈfeɪəɫɪŋ]. You would therefore not have pre-l breaking in falling, killing, kill it, etc.