El canvi de marxes funciona bé.

Literally, canvi de marxes means change of gears.

In real usage, though, it often refers to the gear shift, gear-changing system, or sometimes the gearbox/transmission, depending on context. So yes, it works a bit like a set expression in car-related language, not just a fully literal phrase every time.

De often links two nouns in Catalan, much like of in English.

So:

canvi = change
de marxes = of gears

Together, canvi de marxes means something like gear changing or gear shift. This structure is very common in Catalan:

• tassa de cafè = cup of coffee
• cotxe de carreres = racing car
• canvi de marxes = gear shift / gear changing

Because it refers to gears in general, as a system, not just one gear.

Marxa can mean gear in a vehicle context, and marxes means gears. Since a gearbox or gear shift deals with multiple gears, the plural is natural.

Because canvi is a masculine noun in Catalan, so it takes the masculine singular article el.

So:

• el canvi
• not la canvi

This is something you usually just have to learn with the noun.

In Catalan, when one noun classifies another, de + noun often appears without an article.

So canvi de marxes is a normal way to say gear shift / gear changing system as a general concept.

If you said de les marxes, it would sound more like you are talking about the specific gears already known in the situation. In many cases, that would be less natural here.

Because the subject is el canvi de marxes, which is singular.

The main noun is canvi, not marxes. Even though marxes is plural, it is inside the de phrase and does not control the verb.

So:

• El canvi de marxes funciona bé.
• not funcionen

A good way to check is to ask: what is doing the action of working?
Answer: the gear shift / gearbox = singular.

Because funcionar bé means to work well / function properly.

That is the most natural choice when talking about a machine or mechanical system.

Compare:

• funciona bé = it works well
• està bé = it is okay / it is fine
• és bo/bona = it is good

For a gearbox, funciona bé is the best match if you mean it operates correctly.

Because bé is an adverb, while bo/bona are adjectives.

Here, bé modifies the verb funciona, so it tells us how it works:

• funciona bé = works well

By contrast:

• bo / bona describe nouns
• for example, un bon cotxe = a good car

So the sentence needs the adverb bé, not an adjective.

The accent shows both stress and helps distinguish the word from other forms.

Bé is stressed on that vowel, roughly like bay in English, though not exactly the same.

Also, the accent helps mark it as the adverb meaning well. Written accents are important in Catalan, so it is best to learn them as part of the word.

Yes, El canvi de marxes funciona bé is the most neutral and standard word order: subject + verb + adverb.

You can also say Funciona bé el canvi de marxes, but that sounds more marked, as if you are emphasizing the fact that it works well or introducing the subject later.

So:

• El canvi de marxes funciona bé. = neutral
• Funciona bé el canvi de marxes. = possible, but less neutral

The x in marxes is pronounced like sh in many standard pronunciations, so it sounds roughly like MAR-shəs or MAR-shes, depending on accent.

A rough guide:

• marxa ≈ MAR-sha
• marxes ≈ MAR-shes

The exact sound can vary by dialect, but thinking of x here as a sh sound is a good start.

Yes. Canvi is a common noun meaning change in general.

For example:

• un canvi d’idea = a change of idea
• canvi climàtic = climate change

In canvi de marxes, it has a more specific mechanical meaning because of the context. So the word itself is general, but the full expression becomes specialized.