These mostly come from the reconstructions provided in Wright's Grammar of the Gothic Language, available online as .png files.
I may have made some errors in my transcriptions. Please email any corrections to kesuari at yahoo.com.au. At this stage, very little background information is provided. If you want some, take a look at Wright's Grammar.
Obviously, anything from Proto-Germanic is a reconstruction, but for conciseness, I've generally skipped the traditional asterisk. The yogh (ȝ) and dashed-b from the Grammar are transcribed here as *g and *b, but macrons are still used above long vowels, so a unicode font and recent browser are necessary.
Note that Peter Petersson's page on the Old Norse Language has some information on Proto-Germanic, but as it's not his primary concern, it's poorly formatted. My tables are different from his, I think, so one of us may be wrong. Or Old Norse may have taken the instrumental in some cases, which I mostly lack...
When referring to classes, capital roman numerals (I, II etc.) will be used for strong classes and indo-arabic numerals (1, 2 etc.) will be used for weak classes.
The following table serves as a guide to the ablaut of the various classes of strong verbs. The numbers in the leftmost column refer to the class of strong verbs associated with the ablaut. The first column has the ablaut used in the infinitive and present forms. The second column has the ablaut used in the preterite singular. The third column has the ablaut used in the preterite plural and preterite subjunctive. The final column has the ablaut used for the past participle.
Due to the complexity of the Proto-Germanic verbal system and subsequent simplification in the daughter languages, the titles here might be inaccurate and there are wholes. My apologies.
|1st person||-ō||-ōwiz||-amiz, -amaz|
The imperitive is particularly wholly, with the Gothic being useful for but three forms.
I'm at a loss as to what the infinitive is. I think Wright's Grammar suggested that it was *-onom- in IE, the reflex of which was generalised to all strong nouns in Proto-Germanic. At a guess, I think this means it became *-ana (< *anan < *anam < *onom, though I don't know when (relatively) *o > *a). This could very well be the case; the infinitive in Germanic languages is simple enough, and there's no -s at the end in Gothic which one would expect if it had've been *-anaz.
The present participle is, apparently, an -nd-stem noun. When I decypher §239 of Wright's Grammar, or someone explains it, I'll put it up on the nouns page.
|2nd person||-þa > þ1||-ðiz||-(u)ði|
The past participle is one of *-enaz, *-anaz or *-iniz. I'm not sure whether all three could be used or if there were circumstances surrounding their use
The passive subjunctive is formed from the subjunctive ablaut and the indicative passive inflexion.
There are four classes of weak verbs. They all make use of a preterite involving a dental suffix, of apparently obscure origin. Unfortunately, Wright is rather obscure on the Proto-Germanic forms for many of the moods and tenses.
The preterite suffixes are: 1st p. *-ðōn or *-ðǣn; 2nd p. *-ðǣs; 3rd p. ðǣ. Thus:
|1st person||-ij-ðōn, -ij-ðǣn||-ij-ðōn-wi, -ðǣn-||-ij-ðōn-(u)mi, -ij-ðǣn-|
In all other finite forms, the inflexion is simply *-ij- followed by the equivalent strong suffix (without ablaut). The past participle is *-iðas.
This class contains the decendants of both IE thematic and athematic verbs. The various Germanic languages generalised these in different ways. For instance, Gothic and Old High German generalised the athematic stems, whereas Old English generalised the thematic. As Wright is primarily concerned with Gothic, and that is my main source, I can only show the athematic forms here. However, I am making the assumption that the thematic forms will be similar to the Class 1 forms, simply replacing the *-ij- with *-ō-.
The past participle is *-ōðas and the infinitive *-ōnaz. The preterite indicative and subjunctive are the same as in class 1.