The subject of history of English

ā > ǣ hālian - hǣlan (to heal)

o > oe > e ofstian - efstan (to hurry)

ō > oe > ē wōpian - wēpan (to weep)

u > y kuninʒ - cyninʒ (king)

ū > ȳ mūs - mȳs (mice)

Palatal mutation was found not only in monophthongs but in diphthongs, too. The modified system of diphthongs looks like the following

ea > ie eald - ieldra (elder)

eo > ie feor - fierra (further)

ēa > īe ʒelēafa - ʒelīefan (believe)

ēo> īe ʒetrēowi - ʒetrīewe (true)

In the Northumbian and Merican dialects long and short ea mutate into long and short e (eldra)

We find the reflexes of Old English palatal mutation in such pairs in present-day English as sale - sell; tell – tale; doom – deem.

3.Back, or Velar Mutation

The formula of mutation here reminds very much that of palatal mutation, but the difference is that the syllable that influenced the preceding vowel contained a back vowel - o or u (sometimes even a might serve as background for back mutation).

i > io hira - hiora (their) ; limu - liomu (limbs)

e > eo heorot - heorot (hart); hefon - heofon (heaven)

a > ea saru - searu (armour)
8. Old English Vowels. Phonetic changes( palatalization, contraction, lengthening of Vowels in Certain Conditions)