ذراع المكابح على مقود الدراجة.

Because this is a nominal sentence in Arabic. Arabic often says X on Y without using a verb like is in the present tense.

So the structure is:

• ذراع المكابح = the brake lever
• على مقود الدراجة = on the bicycle handlebar

The verb is is understood:

• ذراع المكابح على مقود الدراجة
• literally: The brake lever on the bicycle handlebar
• natural English: The brake lever is on the bicycle handlebar.

This is very common in Arabic.

Because ذراع المكابح is an iḍāfa construction, often called a possessive construction or noun-noun construction.

In an iḍāfa:

• the first noun does not take ال
• the second noun determines whether the whole phrase is definite or indefinite

So:

• ذراع = arm / lever
• المكابح = the brakes

Together:

• ذراع المكابح = the brake lever / the lever of the brakes

Even though ذراع has no ال, the whole phrase is definite because المكابح is definite.

For exactly the same reason: this is also an iḍāfa.

• مقود = handlebar / steering bar
• الدراجة = the bicycle

So:

• مقود الدراجة = the bicycle’s handlebar / the handlebar of the bicycle

In iḍāfa, the first noun does not take ال, so المقود الدراجة would be wrong here.

The sentence has two main parts:

1. ذراع المكابح
   This is the subject of the nominal sentence.

2. على مقود الدراجة
   This is a prepositional phrase functioning as the predicate.

So the pattern is:

• [subject] + [prepositional phrase]

Very literally:

• Brake-lever of-the-brakes + on + handlebar of-the-bicycle

Arabic and English do not always package meaning the same way.

• المكابح is the plural of مِكبح
• it means brakes

In context, ذراع المكابح means the lever connected with the braking system, so English naturally says brake lever even though Arabic uses the brakes.

This kind of mismatch is normal between languages. You should translate by meaning, not word-for-word.

Yes, ذراع literally means arm, but it can also mean a projecting arm-like part of a device, including a lever.

So in mechanical contexts, ذراع can mean:

• arm
• lever
• control arm
• handle-like projecting piece

Here ذراع المكابح is a natural technical-style phrase for brake lever.

مقود is a general word for a steering/control device.

Depending on context, it can mean:

• steering wheel in a car
• handlebar on a bicycle or motorcycle

Because the sentence says الدراجة (the bicycle), مقود الدراجة is naturally understood as the bicycle handlebar.

على usually means on, on top of, or attached to in many contexts.

Here it shows location:

• على مقود الدراجة = on the bicycle handlebar

This is the natural preposition for something mounted on or attached to a surface or bar.

A careful MSA pronunciation would be approximately:

dhirāʿu l-makābiḥi ʿalā maqūdi d-darrājati

If you ignore case endings, a simpler learner-friendly pronunciation is:

dhirāʿ al-makābiḥ ʿalā maqūd ad-darrāja

A few notes:

• ذ sounds like th in this
• ع is a deep throat sound with no exact English equivalent
• الدراجة is pronounced with assimilation: not al-darrāja, but roughly ad-darrāja, because د is a sun letter

In fully vocalized formal Arabic, the sentence would be:

ذِراعُ المكابِحِ على مَقودِ الدَّرّاجةِ

More precisely:

• ذراعُ = nominative, because it is the subject of the nominal sentence
• المكابحِ = genitive, because it is the second term of the iḍāfa
• مقودِ = genitive, because it comes after the preposition على
• الدراجةِ = genitive, because it is the second term of the iḍāfa مقود الدراجة

In normal unvowelled writing, these endings are usually not shown.

It is definite.

In an iḍāfa, the definiteness of the whole phrase depends mainly on the second noun.

So:

• ذراع مكابح = a brake lever / a lever of brakes
• ذراع المكابح = the brake lever

Since المكابح has ال, the whole phrase is definite.

The same is true for:

• مقود الدراجة = the bicycle handlebar / the handlebar of the bicycle

Yes. Arabic often allows variation in word order.

For example, you could also say:

• على مقود الدراجة ذراعُ المكابحِ

This puts more focus on the location first, somewhat like:

• On the bicycle handlebar is the brake lever

But the original order:

• ذراع المكابح على مقود الدراجة

is straightforward and very natural for learners to understand.

Yes, in many real-life contexts people use فرامل for brakes, especially in less formal usage and in many spoken varieties.

But:

• مكابح is more standard/formal MSA
• فرامل is very common in everyday speech

So in a textbook or formal MSA context, المكابح is a good choice.

Because د is a sun letter.

When ال comes before a sun letter, the l sound is assimilated into the next consonant. So:

• written: الدراجة
• pronounced: ad-darrāja

The spelling does not change, but the pronunciation does.

Word-for-word, yes, that is close to the literal structure. But in normal interpretation, ذراع here is understood as lever, not a human or literal arm.

So the intended meaning is clearly mechanical:

• the brake lever is on the bicycle handlebar

This is a good example of why Arabic should be understood by phrase meaning, not just by the first dictionary meaning of each word.