Ettersom bremsevaieren er gammel og bremsebelegget tynt, må bremsen repareres.

Ettersom introduces a reason clause. In this sentence, it means something like since, as, or because.

Putting it first gives the reason before the result:

• Ettersom ... , må bremsen repareres.
• Reason first, conclusion second.

It is a normal and correct choice, though it can sound a bit more formal or written than fordi in some contexts.

Yes, often you can.

Possible alternatives:

• Fordi bremsevaieren er gammel og bremsebelegget tynt, må bremsen repareres.
• Siden bremsevaieren er gammel og bremsebelegget tynt, må bremsen repareres.

Very roughly:

• fordi = plain, direct because
• siden = since / because
• ettersom = also since / as / because, often a bit more formal or explanatory

In this sentence, all three work.

Because the first part is a subordinate clause introduced by ettersom, and it is followed by the main clause.

Norwegian normally uses a comma between a subordinate clause and a main clause:

• Ettersom ..., må bremsen repareres.

So the comma marks the boundary between:

• the reason: Ettersom bremsevaieren er gammel og bremsebelegget tynt
• the main statement: må bremsen repareres

This is because Norwegian main clauses follow the V2 rule: the finite verb must come in the second position.

Here, the whole ettersom-clause comes first. After that, the main clause begins, and the finite verb må has to come before the subject bremsen:

• Ettersom ..., må bremsen repareres.

If there were no fronted clause, you would say:

• Bremsen må repareres.

So this is normal Norwegian word order after an opening clause.

Because Norwegian usually writes compound nouns as one word.

So:

• bremse
  • vaier → bremsevaier
• bremse
  • belegg → bremsebelegg

This is very common in Norwegian. English often writes similar ideas as two words, but Norwegian usually combines them into one compound noun.

The last part is the main noun:

• vaier is the basic noun in bremsevaier
• belegg is the basic noun in bremsebelegg

In Norwegian, the definite article is often attached to the end of the noun.

So:

• bremsevaieren = the brake cable
• bremsebelegget = the brake lining / the brake pad material
• bremsen = the brake

The endings here are:

• -en for many common-gender nouns
• -et for many neuter nouns

So instead of a separate word like English the, Norwegian often adds a suffix.

It is omitted because it is understood from the first clause.

The full version would be:

• Ettersom bremsevaieren er gammel og bremsebelegget er tynt, må bremsen repareres.

Norwegian often leaves out a repeated verb when two coordinated parts are parallel and the meaning is clear.

So both are possible:

• ... og bremsebelegget tynt
• ... og bremsebelegget er tynt

The version without the second er is concise and natural, especially in written style.

Because the adjectives agree with the noun they describe.

Here:

• bremsevaieren has a noun of common gender singular, so the adjective is gammel
• bremsebelegget has a noun of neuter singular, so the adjective tynn becomes tynt

So:

• en vaier → gammel
• et belegg → tynt

This is adjective agreement in Norwegian.

A few examples:

• Bilen er gammel.
• Huset er gammelt.
• Belegget er tynt.

Because these adjectives are predicative, not attributive.

In other words, they come after er:

• bremsevaieren er gammel
• bremsebelegget er tynt

Predicative adjectives agree in gender and number, but they do not take the definite -e form just because the noun is definite.

Compare:

• den gamle bremsevaieren → attributive adjective before the noun
• bremsevaieren er gammel → predicative adjective after er

So the sentence is correct as written.

Bremsen refers to the relevant brake as a single unit, or to the brake system in the situation being discussed.

In technical or practical language, Norwegian often uses the singular when talking about one brake, one braking mechanism, or the brake assembly being inspected.

If the speaker wanted to refer to several brakes, they could say:

• bremsene må repareres

So singular here is not strange; it just depends on what is meant in context.

Må expresses necessity:

• must
• has to
• needs to

So må bremsen repareres means that repair is necessary.

After må, Norwegian uses the infinitive without å:

• må reparere
• må skifte
• må undersøkes / må repareres

So this is the normal pattern.

Because this is a passive construction.

• reparere = active infinitive, to repair
• repareres = passive infinitive here, to be repaired

So:

• Vi må reparere bremsen = We must repair the brake
• Bremsen må repareres = The brake must be repaired

The passive is used because the sentence focuses on the brake, not on who does the repair.

You could also say:

• Bremsen må bli reparert

That is also passive, but må repareres is shorter and very common, especially in factual or technical language.