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sal_park
10-10-2008, 03:19 AM
Hi,

I'm currently installing heated seats (http://www.bimmernut.com/forum/showthread.php?t=39604) 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 (http://bavtech.com/e34-guides/1995-540i-seats/front-seat-removal.php) (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)
http://bavtech.com/e34-guides/1995-540i-seats/images/seat-belt-retractor-armed.jpg

and a screw to de-active it:
http://bavtech.com/e34-guides/1995-540i-seats/images/seat-belt-retractor-switch.jpg

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

An indicator: (or rather, a hole where it should be)
6003

and a screw (or rather a while cover where it should be):
6002

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
10-10-2008, 04:30 AM
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
10-10-2008, 04:59 AM
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
10-10-2008, 05:02 AM
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
10-10-2008, 05:07 AM
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
10-10-2008, 05:39 AM
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
10-10-2008, 06:48 AM
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
10-10-2008, 07:12 AM
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
10-10-2008, 07:22 AM
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
6004

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
10-10-2008, 07:58 AM
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.
sal_park
10-10-2008, 08:00 AM
Sal, I'll be happy to, just as soon as I stop laughing.

And you have no idea how many times I had to re-write it to make it sound that good :p

oh and thanks btw :)
Ross
10-10-2008, 08:02 AM
Sal,
My cable is also a mere 2 1/2" or so. Yet I am able to satisfy my woman.
sal_park
10-10-2008, 03:30 PM
Sal,
My cable is also a mere 2 1/2" or so. Yet I am able to satisfy my woman.

Thanks Ross.

I'm really confused now :(

It seems that realoem have part numbers for pre-tensioners, with or without electric seats:

with electric seats - 7211 816 7721 / 7211 816 7722

without electric seats - 7211 816 7719 / 7211 816 7720
(these should be mine)


but... the part # on the pre-tensioner is 812 7711
(I've checked it 3 times now - this is definitely correct !)

Not sure what to do now - no obvious way to deactive, but lots of warning on it ("De-activate buckle tensioner before commencing any work on seat") so I'm in doubt that it is a pre-tensioner, I just don't know which one or how to make it safe.
sal_park
10-11-2008, 07:10 AM
right, things are a bit clearer now. I've just got off of the phone with the local dealer and this is what they said:

7211 816 7719 / 7211 816 7720 (as per realoem) are the correct parts for my E34. These are used for E34's from 09/1993 onwards (my E34 was register 08/94 and all of the date stamps are all from 1994 including the pre-tensioner which is dated 25/05/1994)

However, the part in my car (8127711) that I couldn't find on realoem, the guy at the dealership looked up an alternative number using 'view data' (what ever that is) and got an alternative part # of 8140513 which appears to be the part, but is only used for E34's from 09/1992 -> 09/1993. (this 8140513 part # is on realoem).

This tends to suggest that at somepoint after 05/1994 my car was involved with a crash and the pre-tensioners / airbag was replaced with the slightly earier part. This is just a guess though, but it all seems to fit.
sal_park
10-16-2008, 03:32 PM
ok, so after a bit of searching it appears that my 1994 built 525 has sept 92 - sept 93 pre-tensioners in a seat build in 1994 :) Glad that's all straight then !. Basically this tensioner is mechanical only (I think) and the arming / de-arming device can be seen below:

6049

This is below the seat and the butterfly/wing nut thing is how you de-arm it, something like the following:

1. remove tie-wrap (need to replace this when you put it back
2. turn butterfly by 90 degrees and slide out (you'll hear it 'click')
3. remove end of cable
4. relax :)

Here are some useful links:

http://www.pelicanparts.com/bmw/techarticles/JF-Tech/BMW_E36_3_Series_manual_seat_removal.htm

http://www.logun.org/e36frntseat.htm