seatbelt pre-tensionsors

[sal_park]

Hi,

I'm currently installing heated seats and took out the passanger seat yesterday. Because my E34 is a late one, it's got the seatbelt pre-tensionsors installed, which according to the bentley and this page (towards the bottom) should have a green indicator that can be moved to red (made safe) by turning the screw.

So this is what I'm expecting to see:

An indicator: (green = armed)


and a screw to de-active it:


However, when I removed the seat, this is what I can see:

An indicator: (or rather, a hole where it should be)


and a screw (or rather a while cover where it should be):


To me, it looks like the screw hole & Indicator have been covered over and the only reason I can see for this is that they have been activated at some point in the past (i.e. the car has been in a crash). This is quite possible as I've only owned it for the past 5 years, but it's quite scary if this is correct

So what do people think ? Does anyone know if this is how a 'used' pre-tensionsor looks ? All comments welcome

[Ferret]

Does your SRS lamp work correctly? As in does it come on, then go off?

If that pre-tensionner had fired, your lamp would surely stay fixed in the on/flashing position, no?

Unless some unscrupilous person has set it off, then placed a resistive load inside the case to mimic the detonator.

[Omega]

Surly if the pre-tensioned had fired the unit would be shorter that a non-fired unit? The tensioner acts retracting and therefore pulling the belt tight?

Are you sure you actually have pre-tensioners fitted?

[Ferret]

Surly if the pre-tensioned had fired the unit would be shorter that a non-fired unit? The tensioner acts retracting and therefore pulling the belt tight?

Are you sure you actually have pre-tensioners fitted?

From what I remember, if you have an airbag fitted, you HAVE to have pre-tensioners fitted..? If your body's in the wrong place when the airbag goes off, the airbag has enough force that it'll snap your neck like a twig.

[sal_park]

Are you sure you actually have pre-tensioners fitted?

99% sure - I'll check the part number tonight.

Does your SRS lamp work correctly? As in does it come on, then go off?

Yes, this is all working correctly.

If that pre-tensionner had fired, your lamp would surely stay fixed in the on/flashing position, no?

The pre-tensionner is mechincal only, so I can't see how the SRS would know it's been set off (The seat has no electics in it what so ever)

Unless some unscrupilous person has set it off, then placed a resistive load inside the case to mimic the detonator.

A tie-wrap/zip tie has been used in place of the correct part for one of the cables under the seat, so someone has been in there at some point.

[Ferret]

99% sure - I'll check the part number tonight.


Yes, this is all working correctly.


The pre-tensionner is mechincal only, so I can't see how the SRS would know it's been set off (The seat has no electics in it what so ever)


A tie-wrap/zip tie has been used in place of the correct part for one of the cables under the seat, so someone has been in there at some point.

Uhh, does the E34 use mechanical pre-tensioners then? I thought they all used electronic detonation o.O *goes to check*

[Omega]

How does a mechanical pre-tensioner get activated? I was under the opinion they are explosive, electronically triggered.

It does sound like Billy Bodge has been under the seats in the past so anythings possible.

[sal_park]

How does a mechanical pre-tensioner get activated? I was under the opinion they are explosive, electronically triggered.

I'm not sure how it's triggered, but I believe it can be completely mechanical using either a big spring or pyrotechnic charge to tighten the seat belt.

[sal_park]

Right, I've just been out and looked at the other (drivers) seat. The pre-tensioner is identical to the passenger seat (no red/green idicator and a white blanking part where the screw should be). I've also measured the length of the cable between the seatbelt buckle and the pre-tensioner which is about 65mm (see below). If mine has been fired then (according to a friend in the business) we should expect it to have been about 40mm longer, i.e. 105mm (4.1 inches).

Length of pre-tensioner cable, taken from the back seat


Has anyone got 5 minutes to go and measure how long their cable is ? The leather boot (the bit with the velcro) pretty much comes right off (it's clipped on - a little flex will get it off ok with no damage). The difference in length should be fairly obvious.

thanks in advance

[Ross]

Has anyone got 5 minutes to go and measure how long their cable is ?
Sal, I'll be happy to, just as soon as I stop laughing.