Seat Belt – Find the Parts Number & How they Work

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When you are looking to buy a seat belt to replace your old one it is important to match up the part numbers to be sure it’s the correct one for your car. Get it right the first time – You do not want to purchase the wrong one and then go though the process of finding the correct one all over again.

At Your Car Spares Ltd  – What we test and look for!!!!

Before testing a seat belt we look at the condition of it. If the seat belt is fraying or showing signs of deterioration we are unable to keep as it would fail an MOT. If the seat belt is dirty or mouldy then we will keep it but clean it up so it’s in a good and usable condition for the customer. Once we’ve checked the condition of the seat belt we will test it , and this involves us pulling the belt out and looking at how it retracts into the housing , if it doesn’t retract then we won’t keep it. Some cars we get in will have locked seat belts so we try to unlock them but if we are unable to then we can’t keep it.

Where to find a Seat Belt Parts Number

The part number is usually found on a label near the tongue of the seat belt which makes it easy for a customer to match up the part number from their existing part. Below we will show you some examples.

seat belt parts number

Example of where to find the seat belt parts number

View of seat belt

Seat belt part close up view

How does a Seat Belt Work?

In most seat belt systems you will find a retraction mechanism on the belt webbing. In the centre of the retraction mechanism and connected to the end of the webbing is a spool. The spool is responsible for winding the seat belt up so that it’s tight enough to protect the driver , and it’s able to do this because there is a spring that applies rotational force to the spool.

Pulling out the webbing results in the spool rotating counter clockwise and this movement causes the spring to act like it’s being untwisted however , the spring wants to remain the same shape so it resists the movement. Releasing the webbing will cause the spring to tighten and the spool to rotate clockwise until the webbing has returned into the retractor. In case of an accident there is a locking mechanism in the retractor to stop the spool from rotating. The locking mechanism will either work based on the movement on the car or the movement of the seat belt.

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In a system where the locking mechanism works on the movement of the vehicle , there is a pendulum that swings forward if the car suddenly stops. There is a pawl attached to the end of the pendulum which holds onto a toothed ratchet gear on the spool to stop them from rotating counter clockwise.Once the webbing is loose again the gear rotates clockwise causing the pawl to become disengaged.

In a system where the locking mechanism works on the movement of the seatbelt , there is centrifugal clutch mounted to the spool. Once there is sudden movement in the webbing the spool rotates quicker and the centrifugal force forces the lever outwards pushing a cam piece which is joined to a pivoting ball by a sliding pin inside the retractor housing. When the cam shifts in direction the pin moves into the pawl , which results in the pawl going in the spinning ratchet gear and locking into the gears teeth to prevent it from rotating counter clockwise.

Seat Belt Pretensioner

Some modern day vehicles use a pretensioner to pull the webbing to reduce the slack and to put the passenger in the optimum crash position. Some pretensioners will pull the reactor mechanism backwards where as others will rotate the spool. Usually the pretensions are connected to the air bag control module which activates the pretensioners and the air bags upon sudden deceleration on impact through the use of motion sensors.

pretensioner section

View of the pretensioner section

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