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All pictures and texts in this web page are the property of nomaallim.com. Any use of any part of those contents without the written consent of nomaallim.com shall be subject to legal procedures as per international and local laws in the concerned country. Using the name "nomaallim" or "nomaallim com" or "nomaallim.com" in the text describing the unauthorized copied content shall not constitute an exception and shall be sanctioned in accordance to the effective laws and proceedings.
BEFORE YOU START
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DISCLAIMER:
Our pictorials are of informative nature and do illustrate works carried out by ourselves at our own premises for our own use and satisfaction.
Readers who envisage to carry out similar works inspired by the below method shall do this at their own risks and liability.
Our pictorials are of informative nature and do illustrate works carried out by ourselves at our own premises for our own use and satisfaction.
Readers who envisage to carry out similar works inspired by the below method shall do this at their own risks and liability.
NOTE: the below works occurred on Peugeot 5008 MPV but are largely similar or identical on most cars.
Symptoms of a faulty brake booster (vacuum servo)
A brake booster does not fail all of a sudden. Its diaphragm loses of its flexibility / elasticity little by little up to failing completely and eventually get punched. In the meantime, your brake pedal is getting harder and you get used to it while driving without noticing the vacuum servo ageing. Here are the symptoms of an aged brake booster:
- Whistling sound heard inside the car when braking with the hood open (see the below described test)
- Very hard brake pedal at engine idle, gets softer when engine rpm increases
- Very hard brake pedal at first start of the day
- Harder brake pedal when driving at altitude (in mountain, difficult to notice)
- Shorter brake pedal displacement (difficult to notice)
- Unusual longer life of the last fitted front brake pads
How to test the brake booster for whistling sound:
In your car park or a safe road with no traffic, open the hood and move the vehicle a few meters forward and backward. You should here the booster whistle upon braking.
In your car park or a safe road with no traffic, open the hood and move the vehicle a few meters forward and backward. You should here the booster whistle upon braking.
Vacuum servo dismantling - Works inside the engine compartment
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Start by removing whatever blocks the access to your brake booster.
In the particular case of this vehicle (Peugeot 5008), the following has to be removed:
Since the battery seat will also be later removed, I am showing here below how to release the negative battery cable from the battery seat (left) and disconnect its control wire (middle). The right picture shows the booster behind the master cylinder which has to be removed now. |
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Unscrew the master cylinder to take it out however you have to drain it first.
Unscrew the braking circuits outlets each at a time and let the brake liquid flow in whatever container you can fit in there or a thick old towel. Be aware however that in the case of the Peugeot 5008 master cylinder some 1.5L of brake fluid are to be drained which is quite much for a towel to absorb.
In all cases put a metal tray beneath the vehicle to collect any brake fluid that escapes from you.
Unscrew the braking circuits outlets each at a time and let the brake liquid flow in whatever container you can fit in there or a thick old towel. Be aware however that in the case of the Peugeot 5008 master cylinder some 1.5L of brake fluid are to be drained which is quite much for a towel to absorb.
In all cases put a metal tray beneath the vehicle to collect any brake fluid that escapes from you.
Unscrew the brake fluid make-up reservoir, disconnect the brake fluid level sensor and take out the whole set of brake fluid reservoir and master cylinder.
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Brake booster removal - Works inside the vehicle
It is now time to disconnect the brake pedal and unscrew the brake booster.
Start by removing the cover panel beneath the dashboard.
Start by removing the cover panel beneath the dashboard.
Unlink the brake pedal from the vacuum servo.
It is held by a pin in the case of the Peugeot 5008.
Extract the pin as shown in the right picture.
It is held by a pin in the case of the Peugeot 5008.
Extract the pin as shown in the right picture.
One of the four booster nuts is hidden behind the steering column.
A thinner 1/4" handle is used to reach this particular but of difficult access but it should be usually easy on most vehicles to remove the 4 nuts or at least 3 of them.
A thinner 1/4" handle is used to reach this particular but of difficult access but it should be usually easy on most vehicles to remove the 4 nuts or at least 3 of them.
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Extracting the vacuum servo from the vehicle
In the case of the Peugeot 5008, it is necessary to take out the battery seat prior to extracting the brake booster.
Remove all 5 bolts and nuts that do fix the battery tray to the chassis but be aware that a smaller Torx head screw is also to be taken out (right)...
Remove all 5 bolts and nuts that do fix the battery tray to the chassis but be aware that a smaller Torx head screw is also to be taken out (right)...
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...And a bolt hidden behind the mudguard as well.
You can remove this last bolt without removing completely the mudguard as shown in our below pictures:
You can remove this last bolt without removing completely the mudguard as shown in our below pictures:
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Take out the battery support then pull out with both hands the brake booster.
Tilt it either way for finding the space where it can be extracted.
Tilt it either way for finding the space where it can be extracted.
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Refitting the new vacuum servo
In this case, an inner plate fixes the brake booster by holding its bolts temporarily to the chassis prior to refitting the pedals assembly and tightening the nuts. Make sure to fit the plate in its intended place with the four holes of the plate perfectly matching the ones of the chassis.
Now go inside the vehicle and move the pedals in a manner to match also the four holes of the pedals plate with the four holes of the chassis. Temporarily hold the pedals in this position by attaching them to the steering column for example (right) but you can also ask a second person to assist you and hold the pedals in the right place while you push the vacuum servo on the other side.
Now go inside the vehicle and move the pedals in a manner to match also the four holes of the pedals plate with the four holes of the chassis. Temporarily hold the pedals in this position by attaching them to the steering column for example (right) but you can also ask a second person to assist you and hold the pedals in the right place while you push the vacuum servo on the other side.
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Push the new brake booster and reverse all dismantling operations.
Refill and bleed the brake fluid.
Road test your vehicle. You will immediately notice a change in the brake pedal which will now require much less effort to bring the vehicle to a stop.
Refill and bleed the brake fluid.
Road test your vehicle. You will immediately notice a change in the brake pedal which will now require much less effort to bring the vehicle to a stop.
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