Learn Italian: Questa macchina è un disastro, è una macchinaccia! - This car is a disaster, it is a piece of junk!

It uses the derogatory suffix -accia. When added to a noun, this suffix gives the word a bad, ugly, or poor quality. Here, macchina (car) becomes macchinaccia (a terrible car, or a piece of junk).

What happens to the spelling of macchina when we add this suffix?

When adding an alteration suffix like -accia or -accio, you must drop the final vowel of the original word. So, macchina drops its final -a to become the stem macchin-, and then you add the new suffix -accia.

Questa macchina is feminine, so why is it described as un disastro (masculine)?

Adjectives must change to match the gender of the noun they describe, but disastro is a noun, not an adjective. Nouns have their own fixed grammatical gender. Since disastro is always a masculine noun, it takes the masculine article un, even when you use it to talk about a feminine subject like the car.

Does the suffix -accia always mean something is mechanically broken?