O guiador e o cabo de travão precisam de ajuste.

Because the subject is plural: O guiador e o cabo de travão = the handlebar and the brake cable.

In Portuguese, the verb has to agree with the subject:

• O guiador precisa = the handlebar needs
• O cabo de travão precisa = the brake cable needs
• O guiador e o cabo de travão precisam = the handlebar and the brake cable need

So precisam is the 3rd person plural form of precisar.

In European Portuguese, precisar usually takes the preposition de when it means to need.

So:

• precisar de algo = to need something
• precisar de ajuste = to need adjustment

This is very common and standard in Portugal.

Examples:

• Preciso de ajuda. = I need help.
• Ela precisa de descanso. = She needs rest.

So in this sentence, precisam de ajuste is the normal structure.

Guiador usually means handlebar in European Portuguese, especially for a bicycle, motorbike, or similar vehicle.

For a learner, it helps to think of it as:

• guiador = the part you hold to steer

It comes from the idea of guiding/steering.

In this sentence, o guiador most naturally means the handlebar.

Literally, it is something like brake cable.

Breakdown:

• cabo = cable
• travão = brake

The structure noun + de + noun is very common in Portuguese and often corresponds to an English compound noun.

So:

• cabo de travão = brake cable
• literally, cable of brake

English often puts the first noun before the second, but Portuguese commonly uses de.

In European Portuguese, travão is the usual word for brake in this kind of context.

In Brazilian Portuguese, freio is more common.

So for Portugal:

• travão = standard and natural

For Brazil:

• freio would often be preferred

This is a useful European/Brazilian vocabulary difference.

Here, ajuste is a noun meaning adjustment.

So:

• precisam de ajuste = need adjustment

Portuguese often uses a noun where English might say:

• need adjustment
• need an adjustment
• need to be adjusted

All of these are close in meaning.

You could also say:

• precisam de ser ajustados = need to be adjusted

But precisam de ajuste is shorter and very natural, especially in technical or mechanical contexts.

Because ajuste is being used in a general sense: they need adjustment.

Portuguese often omits the article in expressions like this when talking about something non-specific or as a general requirement.

Compare:

• precisam de ajuste = they need adjustment
• precisam de um ajuste = they need an adjustment

Both can work, but they are slightly different:

• de ajuste sounds more general or technical
• de um ajuste sounds a bit more like one specific adjustment

In a maintenance context, precisam de ajuste sounds very natural.

Yes. The full subject is:

• O guiador e o cabo de travão

This is a compound subject joined by e = and.

Then the predicate is:

• precisam de ajuste

So the sentence structure is:

• Subject: O guiador e o cabo de travão
• Verb phrase: precisam de ajuste

That is why the verb is plural.

Yes, but this is an important point.

In European Portuguese, precisar de is the normal choice when meaning to need.

In some varieties, especially in Brazilian Portuguese, you may sometimes hear precisar used directly with an object, without de. But for Portugal, learners should strongly prefer:

• precisar de

So in this sentence, precisam de ajuste is exactly what you should expect in European Portuguese.

Yes, absolutely.

That version means:

• The handlebar and the brake cable need to be adjusted

It is more explicit about the action.

Compare:

• precisam de ajuste = need adjustment
• precisam de ser ajustados = need to be adjusted

The original sentence is a little more compact and technical-sounding, but both are natural.

The ending -ão is a very common Portuguese nasal sound.

In travão, the stress is on the last syllable:

• tra-VÃO

The ão is nasal, not like a normal English ow sound. A rough approximation is something like owng, but without clearly pronouncing the final g. It is better to think of it as a nasal vowel rather than a sequence of separate sounds.

This same ending appears in many common words:

• mão = hand
• pão = bread
• razão = reason

For European Portuguese, the nasal quality is especially important.

Because O belongs only to the first noun, guiador.

The sentence is really:

• O guiador = the handlebar
• e = and
• o cabo de travão = the brake cable

So both nouns have their own article:

• O guiador e o cabo de travão

Portuguese often repeats the article before each noun when listing specific things.

If you removed the second article, the meaning or rhythm could change, and it would sound less natural here.