Kočnice rade dobro.

Kočnice means brakes. It is the plural form of kočnica = brake.

It is plural because in English and Serbian, brakes are often talked about as a set: the brakes. So Kočnice rade dobro literally matches The brakes work well.

Grammatically, kočnice here is in the nominative plural, because it is the subject of the sentence.

The singular is kočnica = brake.

So:

• Kočnica radi dobro. = The brake works well.
• Kočnice rade dobro. = The brakes work well.

Notice the verb changes too:

• singular: radi
• plural: rade

Rade is the 3rd person plural present tense of raditi, which often means to work, to function, or to operate.

In this sentence, it means are working / function:

• Kočnice rade dobro. = The brakes work well.

Serbian often uses raditi for machines, systems, and parts when they function properly:

• Motor radi. = The engine is working.
• Telefon ne radi. = The phone isn’t working.

So using rade for brakes is very natural.

Because the subject is plural.

• kočnica → singular → radi
• kočnice → plural → rade

So the verb agrees with the subject:

• Kočnica radi dobro.
• Kočnice rade dobro.

This is a basic agreement pattern in Serbian.

Here dobro is an adverb, meaning well.

So:

• raditi dobro = to work well

It is not an adjective here, so it does not change to match kočnice.

Compare:

• Kočnice rade dobro.
  = The brakes work well.
  Here dobro describes how they work.

• Kočnice su dobre.
  = The brakes are good.
  Here dobre is an adjective describing the brakes themselves.

That is why dobro is correct in your sentence.

Yes. Serbian present tense often covers both:

• The brakes work well
• The brakes are working well

Which English translation sounds best depends on context.

In a general statement, The brakes work well is often best. In a situation where someone is checking them right now, The brakes are working well can also fit.

Serbian has no articles like a / an / the.

So Kočnice can mean:

• brakes
• the brakes

The exact meaning depends on context.

This is very normal in Serbian. You do not need to add a separate word for the.

Yes, Serbian word order is more flexible than English.

The neutral, standard order here is:

• Kočnice rade dobro.

But other orders are possible for emphasis, such as:

• Dobro rade kočnice.
• Kočnice dobro rade.

These all mean roughly the same thing, but the emphasis changes slightly. For learners, Kočnice rade dobro is the safest and most neutral version.

Yes, it is a normal and natural sentence.

A Serbian speaker might also say:

• Kočnice dobro rade.
• Kočnice funkcionišu dobro.

But raditi is extremely common for functioning / working properly, so Kočnice rade dobro sounds natural.

A simple pronunciation guide is:

• Kočnice ≈ KOCH-nee-tseh
• rade ≈ RAH-deh
• dobro ≈ DOH-broh

A few useful notes:

• č sounds like ch in chocolate
• c sounds like ts in cats
• Serbian pronunciation is usually quite regular, so words are often pronounced much as they are written

Yes, but it means something slightly different.

• Kočnice rade dobro. = The brakes work well.
  Focus: how they function

• Kočnice su dobre. = The brakes are good.
  Focus: their quality

In real life, these can overlap, but grammatically they are not the same.

The dictionary forms are:

• kočnica = brake
• raditi = to work, to function
• dobro = well / sometimes good depending on use

In the sentence:

• kočnice = plural form of kočnica
• rade = present plural form of raditi
• dobro = adverb meaning well