Ad. [w] and [j] became [u] and [i] before consonants and finally; [wC|-w|jC|-j] > [uC|-u|iC|-i]
Tolkien stated that the semi-vowel [w] was vocalized to the vowel [u] when appearing before a consonant or finally. In similar conditions the semi-vowel [j] became [i] (SD/419).
There is some ambiguity of whether this w/y-vocalization happened before or after [ɣ] assimilated to preceding voiced consonants. Either way, the net result would have been the same. In the first case, ✶[wɣV/yɣV] would have become [uɣV/iɣV] and thereafter [uwV/uyV] when [ɣ] became [w], [j] between [u], [i] and another vowel. In the second case, the [ɣ] in ✶[wɣV/yɣV] would have assimilated to [wwV/yyV] before the vocalization could apply, and thereafter became [uwV/uyV]. The discussion here assumes w/y-vocalization happened first, since it simplifies some other rules. See the word ✶dāw’r for more evidence that this vocalization was early.
Reference ✧ SD/419
Phonetic Rule Elements
||✧ SD/419 ([wC|-w] > [uC|-u])|
||✧ SD/419 ([yC|-y] > [iC|-i])|
Phonetic Rule Examples
|izrajji > izraiji||jC|-j > iC|-i||✶Ad. izray+yi > izrai+yi > izrēyi > izrêi > Ad. izrê||✧ SD/424|
|dāwr > dāur||wC|-w > uC|-u||✶Ad. dāw’r > Ad. dâur||✧ SD/423|
|khāw > khāu||wC|-w > uC|-u||✶Ad. khāw > Ad. khâu||✧ SD/426|
|khaw > khau||wC|-w > uC|-u||✶Ad. khăw > Ad. khō||✧ SD/426|
|manaw > manau||wC|-w > uC|-u||✶Ad. manaw- > manau > Ad. manō||✧ SD/424|
|manawji > manauji||wC|-w > uC|-u||✶Ad. manaw+yi > manau+yi > manōyi > Ad. manôi||✧ SD/424|