Hey guys, this is a bit weird, but there is a first time for everything

This Sunday me and my friend were having a bite, while the car was parked just next to us, under the perfect Sunday sun (possibly around 28-30C). Then I hear a "hit", like a ball hitting the car, when the jag's alarm sounded off. As the car was next to us we saw nothing to have had contact with the car. What happened is baffling The driver's seat was pulled to the back (my friend was driving the jag and he is way smaller ) and the seat belt was locked! It is not moving in any direction. Just to clarify, the seat belt (driver side, LHD) wasn't hooked on or anything.

From what I gather the pretension probably has blown up. As my shop will take couple of days before being able to look at the car I wanted to try and mend it at least temporarily and was wondering what exactly is the setup of the seat belt. Is the pretensioner in the XK8 with the lock next to the seat or is it in the seat belt pulley. Can the pulley be unlocked to work again, and can the pretensioner be changed or I need a new seat belt. And when talking about a new seat belt is there a difference between the seat belts in LHD and RHD cars, as here in Europe it is easier to find parts from RHD cars... Also does XK8 share the seat belt with other models?

And finally what could have caused that, and should I prepare for an airbag to the face at some point

 

The pre-tensioner is in the reel assembly:



This is the description from JTIS workshop manual:

Each front seat belt has a pyrotechnic device with independent mechanical sensing and pre-tensioning retractor unit, installed at the base of the 'B' post. In the event of severe frontal impact, this provides additional occupant protection by removing any excess slack from the seat belt. Seat belt pre-tensioning activates when a frontal impact of sufficient force occurs within 30 degrees of vehicle center line. Under such an impact, mechanical sensors in the retractor unit fire, igniting the pre-tensioner gas generator. The gas generator initiates a chemical reaction, producing gases under pressure. Gas pressure drives the piston/cable up a tube, rotating the retractor spindle and removing excess slack from the seat belt. The mechanical sensor is made live by screwing the arming pin in to fully depress the red arming button.

The pre-tensioning system can only be activated if a safety lever is re-set by fitting the associated belt to an occupant or child seat. When the pre-tensioner unit has been activated, the seat belt will lock and cannot be retracted or pulled from the reel.

The Parts Catalogue shows the seat belts and the seatbelt buckles are handed - separate P/N's for LH and RH sides of the vehicle. It doesn't matter whether the car is LHD or RHD so you could source a LH seatbelt from a UK RHD or European LHD car.

Graham

 

Thank you! This should be of help.

 

before you install a replacement unit be very certain that there is nothing electrically wrong. this system should never activate outside of the set parameters. if someone is handling the unit and attaches the wiring harness, they could be injured by an unanticipated activation. at minimum the car should be depowered during installation. i would check for proper voltage and resistance at the electrical connector. this could be due to a wiring harness short or a failing SRS module. this means that your airbags could be next, both expensive and dangerous if they deploy outside of scope. do not drive the car and depower it until it is properly evaluated. was the vehicle ever in a collision? i do not know if the vehicle has any electrical connection to the seatbelt pretensioner, but this should be investigated thoroughly. perhaps something in the area came into contact with the unit such as live electrical wire.

 

Fortunately (or not) I was right to assume a blown pretenssioner, as apparently this is exactly what have happened. The mechanic told me that the pretenssioner is fully mechanic (not sure how that works exactly..) and that they could only assume it was a malfunction in the pretenssioner itself - old age, high temperature, etc. The sad part is that they claim they cannot unlock the belt, so I can use it until the new one arrives (I'm just after a classic/retro event at the end of the month ). It wasn't easy to source a second hand belt, but I managed to order one (the dealer's quote was a bit too much, and the shipment time was like a month...)

 

The pyrotechnic pre-tensioner should only activate only if the seat belt is in use. The incident you described in post #1 suggests either a fault in the pre-tensioner unit or a harness fault. If it was harness fault, the replacement could also go off unexpectedly.

Graham

 

As I understand there is no harness going to the pre-tenssioner. It is fully mechanic. As I see there are couple of different seat belt assemblies, that weirdly are not dependent on the production year, as the one I ordered is from a 2001 car, and some that were quoted for 1996 to 2002 were totally different (probably for US models idk). Still I'll make them double check before installing the new one.

 

 

Well... yesterday my mechanic informed me that while he was working on fixing my TCM, he got the box with the leftover seat belts out of the trunk, only for the right one (that I ordered but was incomplete) to blow up several minutes after that The car was sitting in the shop a full day by then, so there was no direct sunlight heating up the car. So my theory of them overheating is unsound