De monteur zegt dat ook de achterste rem vervangen moet worden.

Dat introduces a subordinate clause, like English that in The mechanic says that...

So the sentence has two parts:

• De monteur zegt = the mechanic says
• dat ook de achterste rem vervangen moet worden = that the rear brake also has to be replaced

In everyday English, that is often omitted, but in Dutch dat is very common here.

Because dat starts a subordinate clause, and Dutch usually sends the verb group to the end of that clause.

Compare:

• Main clause: Ook de achterste rem moet vervangen worden.
• Subordinate clause: ...dat ook de achterste rem vervangen moet worden.

That end-of-clause verb placement is one of the most important Dutch word-order patterns to get used to.

Monteur usually means a mechanic, repair technician, or installer, depending on context.

It is a practical, job-related word for someone who works on machines, vehicles, or technical equipment. In this sentence, mechanic is the most natural interpretation.

Here ook means also or too, and its position shows what is being added.

• dat ook de achterste rem ... emphasizes that the rear brake too is included
• in other words, something else probably already needed attention, and now the rear brake is being added to the list

If you move ook, the emphasis can shift slightly. Dutch uses word order a lot to signal focus.

Achterste means rear, back, or more literally the one at the back.

Dutch often uses forms like:

• voorste = front
• achterste = rear / back
• bovenste = top / upper
• onderste = bottom / lower

These look like superlatives, but in practice they often function as ordinary positional adjectives. So de achterste rem means the rear brake.

There are two things going on:

1. rem is a de-word, so it takes de
2. adjectives before a noun usually take an -e ending

So:

• de rem
• de achterste rem

That is the normal attributive pattern in Dutch.

Because the subject is singular: de achterste rem.

So the verb agrees with that singular subject:

• de rem moet
• de remmen moeten

Even though English sometimes uses structures that feel less obviously singular, Dutch still matches the verb clearly to the noun.

This is a passive construction with a modal verb.

• vervangen = replaced
• moet = must / has to
• worden = be

Together, moet worden vervangen means must be replaced.

In this sentence, because it is a dat-clause, the verb group appears at the end as vervangen moet worden.

So the structure is basically:

• subject: de achterste rem
• passive + modal meaning: must be replaced

Here it is a past participle, even though it looks identical to the infinitive.

That can be confusing, but it is normal with some Dutch verbs. The verb vervangen has:

• infinitive: vervangen
• past participle: vervangen

This happens because ver- is an inseparable prefix, so the past participle does not get ge-.

In the passive with worden, Dutch uses the past participle, so here vervangen means replaced, not to replace.

Yes. Dutch verb clusters often allow more than one order, especially in subordinate clauses.

So both of these are possible:

• ...dat ook de achterste rem vervangen moet worden
• ...dat ook de achterste rem moet worden vervangen

The sentence you were given is completely natural. The alternative is also common. Learners should mainly understand that in a subordinate clause, the whole verb cluster moves toward the end.

Dutch can do both.

• achterrem = rear brake
• achterste rem = the rearmost / rear brake

The compound achterrem is very common, especially when naming a part directly.
Achterste rem is a bit more descriptive and can sound like you are identifying which brake you mean, especially in contrast with a front brake.

So the sentence is normal, even though a compound version is also possible.

Yes, but the singular here means one specific brake is being discussed.

• de achterste rem = the rear brake
• de achterste remmen = the rear brakes

Whether singular or plural is used depends on what part the speaker sees as the unit being replaced. In repair language, singular often refers to one specific component, even if English might sometimes talk more loosely about the brakes.