Má phanh bị mòn.

A natural word-by-word breakdown is:

• má phanh = brake pad / brake lining
• bị = a marker often used when something is in an affected, often undesirable, condition
• mòn = worn, worn down, abraded

So the structure is basically:

• má phanh
  • bị mòn
• the brake pad(s)
  • are worn down

Because phanh means brake in general, while má phanh refers to a specific part of the brake system: the brake pad or brake lining.

So:

• phanh = the brake system / brake mechanism
• má phanh = the pad/lining that presses by friction

This is similar to the difference between:

• brake and
• brake pad

Yes, má can mean cheek in other contexts, and in some dialects it can also mean mother. But in má phanh, it is part of a fixed technical term meaning pad, lining, or a flat contact piece in machinery.

So this is a good example of why Vietnamese compounds should often be learned as a unit:

• má phanh = brake pad / brake lining

You should not interpret it literally as cheek brake.

bị shows that something is in a state caused by an unpleasant or unwanted process. It often carries an idea like:

• to suffer
• to be affected by
• to end up in an undesirable condition

In Má phanh bị mòn, it suggests the brake pad has undergone wear and is now in that worn condition.

So bị is not just a random filler word. It adds the sense that the part has been affected negatively.

It is similar to a passive idea, but not exactly the same as English passive in every case.

English might say:

• The brake pads are worn.
• The brake pads have been worn down.

Vietnamese bị often overlaps with passive-like meaning, especially when something is adversely affected. But it is better to think of it as marking that the subject is undergoing or has undergone an unwanted condition, rather than trying to force it into English grammar labels.

So yes, it can feel passive, but its function is broader than English passive voice.

Yes, you can, and it would still be understandable.

• Má phanh mòn = The brake pad is worn.
• Má phanh bị mòn = The brake pad has become worn / is affected by wear.

The version with bị sounds a bit more like the speaker is emphasizing the resulting problem or deterioration.

In technical or everyday speech, both may appear, depending on style and emphasis.

Vietnamese often does not use a verb equivalent to to be in sentences like this.

English:

• The brake pads are worn.

Vietnamese:

• Má phanh bị mòn.

This is very normal. Vietnamese frequently links the subject directly to a state or description without needing a separate word for is/are.

By itself, má phanh does not clearly mark singular or plural. It can mean:

• a brake pad
• brake pads

The exact meaning depends on context.

If Vietnamese wants to be more specific, it can add words such as:

• một má phanh = one brake pad
• các má phanh = the brake pads / multiple brake pads

But very often Vietnamese leaves number unmarked when it is already understood.

mòn means worn down through friction, use, or erosion.

It is commonly used for things that gradually lose material or thickness, such as:

• lốp xe mòn = the tire is worn
• dao mòn = the blade is worn
• đế giày mòn = the shoe sole is worn

So in Má phanh bị mòn, the idea is that the brake pad has been reduced or thinned by use.

Not necessarily. Vietnamese often leaves time and aspect to context.

• Má phanh bị mòn can already mean the brake pad is in a worn condition now.
• Má phanh đã bị mòn makes it more explicit that this condition has already occurred.

So:

• without đã = natural, general statement of condition
• with đã = clearer emphasis on completion or prior change

In many real situations, the shorter version is perfectly normal.

A rough pronunciation guide is:

• má — rising tone
• phanh — level tone
• bị — heavy/low tone
• mòn — falling tone

Very rough English-style approximation:

• maa phanh bee maw(n)

But the tones matter a lot, especially on:

• má
• bị
• mòn

If you ignore tones, people may still sometimes guess from context, but the pronunciation will sound much less natural.

Yes. In some southern usage, thắng is also used for brake.

So you may hear:

• má phanh
  or
• má thắng

Both relate to brake pads/linings, though phanh is the standard term you will see widely in formal or technical Vietnamese.

Yes. Because of bị and the meaning of mòn, the sentence naturally sounds like a mechanical issue that needs attention.

Depending on context, it can function as:

• a diagnosis
• a warning
• a note in a repair report
• a mechanic’s observation

So even though the sentence is short, it often implies:

• The brake pads are worn, and that is a problem.