"Mathilde a rentré la voiture avant qu'il ne pleuve." - why not a past tense of the subjunctive mode?

Question

My mind gets quite confused by combining the past with the present (subjunctive) in one sentence. This is more a question about the subjunctive mode than about rentrer, but could you explain in which situations you use le passe of the subjunctive? If this sentence used parce que, rather than avant que, what tense would you use? (something like "Mathilde a rentre la voiture parce qu'il allait pleuvoir"? - sorry, no accents; if this structure exists, I wouldn't know what the tense is called!)

Thanks in advance for your clarification!

Accepted Answer

Some time ago, French used to have all the tenses represented in indicative as well as subjunctive mood. Today, all but the subjunctive present tense and past tense have disappeared. You may encounter some of the other subjunctive tenses in written French occasionally, but they're as good as extinct.
 
That said, how the tenses in the subjunctive mood are used, by necessity, has changed also. You employ the past subjunctive mostly to indicate that one action ended before the other started. The present subjunctive is used in pretty much all other cases. It isn't so much when the action takes place. The past subjunctive emphasizes the temporal relationship.

Answer

Bonjour Mathilde,
Mathilde a rentré la voiture parce qu'il allait pleuvoir = Mathilde put the car back (in the garage) because it was going to rain -> Indicative mood (used for facts and real situations) - Imparfait
Take a look at the links below:
French Present Subjunctive
French Past Subjunctive
I hope this is helpful.
Bonne journée !

Answer

Mathilde a rentré la voiture parce que il allait pleuvoir. -- Mathilde brought the car in because it was going to rain.Yes, the tense of allait is the 3rd person singular imperfect, indicative mood, of the verb aller. Note that "was going to" in the English translation is also 3rd person indicative mood in imperfect tense. So no surprise here.