In word final position, or de facto word final
position after loss of a final vowel
(see section 4, Weakening), or immediately before final s, v preceded by a short
vowel is commonly vocalized to u; thus :
savs is normally pronounced (saus)
sev is normally pronounced (seu)
zivs is normally pronounced (zius)
krav(u) is often pronounced (krau).
Note in particular that nav is almost always pronounced (nau).
After a long vowel or diphthong, the vocalization is much less common.
If the following word begins with a vowel, the final or de facto final v is more
likely to retain its consonantal articulation. Notice particularly that under
these circumstances the word jau will often be pronounced (jav).
T.G. Fenell. H. Gelsen