Sejam os freios, sejam os pneus, tudo precisa de revisão.

It introduces alternatives in a formal, emphatic way.
Here, sejam os freios, sejam os pneus works like:

• whether it be the brakes or the tires
• be it the brakes or the tires

So the repeated form helps express it doesn’t matter which of these you mean; the statement still applies.

Because this is not a simple statement like they are the brakes or they are the tires. It is a special structure that uses the subjunctive of ser to present alternatives.

• são = present indicative, used for straightforward statements
• sejam = present subjunctive, used here in a set pattern like whether it be...

So sejam is the correct form for this kind of expression.

Sejam is from the verb ser.

In this sentence, it is the present subjunctive, 3rd person plural form of ser.

The full subjunctive set is:

• eu seja
• você/ele/ela seja
• nós sejamos
• vocês/eles/elas sejam

Because it matches the plural nouns that follow:

• os freios = plural
• os pneus = plural

So Portuguese uses sejam rather than seja.

If the noun were singular, you would normally use seja, for example:

• Seja o motor, seja a suspensão...

Sometimes, yes, but not perfectly in every context.

Sejam ..., sejam ... is closer to:

• whether it be ... or ...
• be it ... or ...
• whether ... or ...

It often sounds a bit more formal or rhetorical than plain either...or... in English.

Portuguese uses definite articles more often than English does.

Here, os freios and os pneus can refer to:

• the specific brakes and tires of the vehicle being discussed, or
• those parts as known categories in the situation

In English, we often drop the article in similar cases, but Portuguese commonly keeps it.

Sometimes, yes, but it would not sound exactly the same.

For example:

• Freios e pneus precisam de revisão.

That sounds more like a general statement or a simple list.
With os freios, os pneus, the sentence feels more tied to a specific vehicle or a more defined situation.

So the version with articles is very natural.

Because the verb agrees with tudo, not with freios or pneus.

And tudo is grammatically singular in Portuguese.

So:

• tudo precisa
• not tudo precisam

Even if tudo refers to several things together, it still takes a singular verb.

Yes. In Portuguese, tudo can mean everything / all of it / all that and summarize the items just mentioned.

So after naming os freios and os pneus, the speaker can use tudo to mean all of that.

If you wanted to be more literal, you could also say:

• os dois precisam de revisão
• ambos precisam de revisão

But tudo is natural if the idea is that the whole set of relevant parts needs attention.

Because the verb precisar, when it means to need, normally takes de in standard Portuguese.

So:

• precisar de algo = to need something
• precisa de revisão = needs inspection / servicing

This is the safest and most standard structure to learn.

Because Portuguese often uses a bare noun after de in expressions like this, especially when talking about a type of need in a general sense.

So:

• precisa de revisão = needs checking / needs servicing

If you say:

• precisa de uma revisão

that can sound a bit more like needs a check-up / needs one service inspection.

Both are possible, but the version without the article is very common.

Not here.

In a vehicle context, revisão usually means something like:

• inspection
• check-up
• servicing
• maintenance review

So this is a false-friend situation.
English revision often refers to changing or editing a text, or studying again. Portuguese revisão can do that too in other contexts, but here it is clearly mechanical.

Yes, it is correct and natural, but it sounds somewhat more formal or polished than everyday casual speech.

In conversation, many Brazilians might say something simpler, such as:

• Os freios e os pneus precisam de revisão.
• Sejam os freios ou os pneus, tudo precisa de revisão.

The original version has a slightly more rhetorical, written feel. It is good Portuguese, just not the most casual way to say it.