Bremsen på sykkelen virker ikke.

Because bremsen is the definite singular form: the brake.

• en brems = a brake
• bremsen = the brake

In this sentence, you are talking about a specific brake, not just any brake.

For the same reason: sykkelen is the definite singular form, meaning the bicycle / the bike.

• en sykkel = a bicycle
• sykkelen = the bicycle / the bike

So på sykkelen means on the bike.

Here på means on.

So bremsen på sykkelen literally means the brake on the bike.

Norwegian often uses på for something attached to or belonging to an object in a physical sense:

• døra på bilen = the door on the car
• taket på huset = the roof on the house

So this is a very normal way to say it.

Because in a normal Norwegian main clause, ikke usually comes after the finite verb.

Here the finite verb is virker:

• Bremsen på sykkelen virker ikke.

That is standard Norwegian word order.

Compare:

• Han kommer ikke. = He isn’t coming.
• Det fungerer ikke. = It doesn’t work.

English puts not differently, but Norwegian usually places ikke after the verb in simple main clauses.

Here virker means works / is functioning.

It is the present tense of å virke.

• å virke = to work, to function, sometimes to seem
• virker = works / is working / seems, depending on context

In this sentence, the meaning is clearly functions:

• Bremsen virker ikke = The brake doesn’t work

Yes. Fungerer ikke is also completely natural.

• Bremsen på sykkelen virker ikke.
• Bremsen på sykkelen fungerer ikke.

Both mean the brake on the bike doesn’t work.

A small nuance:

• virker is very common in everyday speech
• fungerer can sound a little more explicitly like functions

But in this sentence, both are fine.

Yes, but Norwegian can still use the singular if you mean:

• one specific brake, or
• the brake system in a general, everyday way

So bremsen på sykkelen may refer to the brake as the relevant brake being talked about.

If you want to be clearly plural, you could say:

• Bremsene på sykkelen virker ikke. = The brakes on the bike don’t work.

This is a very common Norwegian structure:

• X på Y = the X on/of Y

So:

• bremsen på sykkelen = the brake on the bike
• hjulet på bilen = the wheel on the car
• døra på huset = the door of the house

English often uses of or an apostrophe, but Norwegian very often uses på in these physical-object relationships.

Because the sentence refers to a specific brake and a specific bike.

This is very natural in Norwegian when talking about a part of a known object:

• bremsen på sykkelen
• døra på bilen
• vinduet i huset

English might sometimes be less definite in similar situations, but Norwegian commonly makes both nouns definite when both are identifiable in context.

Yes, grammatically you can. It means the bike’s brake doesn’t work.

But it is usually less natural in everyday speech than:

• Bremsen på sykkelen virker ikke.

Norwegian often prefers the X på Y structure over a genitive form like sykkelens in ordinary spoken-style language.

So your original sentence is the more natural everyday version.

You can, but it changes the feel of the sentence.

• Bremsen på sykkelen virker ikke naturally identifies which brake
• Bremsen virker ikke på sykkelen can sound more like it doesn’t work when used on the bike, or it gives the location later for emphasis

So the original word order is the clearest and most natural if you simply mean the bike’s brake doesn’t work.

The pattern is:

subject + verb + ikke

Here:

• Bremsen på sykkelen = subject
• virker = verb
• ikke = negation

So the full structure is:

• Bremsen på sykkelen
  • virker
    • ikke

This is a very useful pattern to remember for simple Norwegian statements.

In the plural, you would say:

• Bremsene på sykkelen virker ikke.

Breakdown:

• bremsene = the brakes
• på sykkelen = on the bike
• virker ikke = don’t work

So this means The brakes on the bike don’t work.