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What Does The Brake Vacuum Booster Do?

Believe it or not, your leg isn’t strong enough to stop a car just by stepping on the brake pedal. Due to the way that levers work, the brake pedal would have to move about 50cm to brake a car just using muscle power. Because that’s not possible, the brake vacuum booster amplifies your strength so the brake pedal can have less movement but still output enough power.

When you are braking, you let off the accelerator which closes the throttle body. This creates a vacuum in the inlet manifold. This vacuum is sent to the brake vacuum booster to help pull on one side as you push on the other side. If you want a more detailed insight, have a look at this video.

What Happens If It Fails?

The brake pedal can feel hard but the actual braking seems weak. Depending on the model, you can get a warning on the speedo telling you there’s a brake fault and to throw money at a dealer.

Where Is The Brake Vacuum Booster?

Open the bonnet and look for the brake fluid reservoir (black cap with DOT 4 written on it). The brake vacuum booster is the large silver or black disc behind it.

Remove the scuttle panel, wiper mechanism and brake master cylinder. Then it’s time to get the screen wash filler neck out of the way. If you have a left hand drive car, you’re lucky because the tank is 1 piece and easy to remove. Find the clip that secures the filler neck to the front frame…

…and remove it. You can now twist and pull the filler neck from the washer bottle.

On the right hand drive model you now have to move the washer tank out of the way. Luckily you don’t have to remove it fully.

Over to the left is a bolt that goes through the frame and into the top of the washer bottle. It’s awkward and slow but you can remove this bolt without removing the front panels and the headlight. If you have no dexterity at all, remove the front panels and the headlight to gain access to the bolt.

Pull the bottle upwards. This disconnects it from a rubber grommet underneath. You can now scoot it sideways and down to give you room.

Finally you can see the brake vacuum booster.

Take a run up and launch yourself into the driver’s footwell. Look at the top of the brake pedal lever. You’ll see where the brake vacuum booster arm connects to the brake pedal. Remove the blue plastic C clip. It comes off very easily.

Look at the brake vacuum booster arm and you’ll see a swing clip. Lift it up to unclip it and it’ll swing upwards and towards the rear of the car.

You can then pull the whole clip to the right to disconnect the brake pedal from the brake vacuum booster rod.

This is the removed clip so you can understand how it works.

With a 13mm socket, ratchet, universal joint and several extensions, you’ll be able to remove the 4x nuts holding the brake vacuum booster to the bulkhead.

Back to the front of the car. Pull the brake vacuum booster forwards and away from the car.

Clean up the mating surface before fitting the replacement.

You can see more clearly the bend in mine. Apparently many Renault ones are a direct replacement but I’ll leave that up to you to determine as I can’t be sure. I bought a replacement from a Renault Twingo Mk3 which is the same part but it arrived broken so I had to buy a new replacement from smart.

When you fit the new brake vacuum booster, make sure it’s up the correct way, get a friend to hold it in position as you replace the nuts holding it to the car, lubricate the rubber seals before refitting the pressure sensor and vacuum pipe.