Granted this is not exactly diesel specific, but there are way more and better responses here than anywhere else. Had to go into the area behind the pillar cover by the back of the front seats on a couple of 300D's recently. Noticed that the seat belt retractor on the '83 was fairly simple and basically all mechanical. On the '85, which has an alarm system, there is a piece of pipe about 8 to 10" long sticking up out of the retractor with another small cylinder coming off at right angles to that. The small cylinder has a wire going to it and it appears that there is a cable coming from the retractor and going up into the 10" vertical pipe. What is this and what does it do? Is it related to the vehicle year or an addition due to the alarm system? TIA....

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1961 190Db retired
1968 220D/8 325,000
1983 300D 164,150

Hello Lycoming,

These tubes I believe they are belt "spanners" .
They put tension on the belts in case of a (frontal) collision and so assit
to keep the body in place. To provide the necessary speed and energy to react in some miliseconds, it works as an airbag : powered by explosives and triggered by an electric circuit.
So one advice : unless you know exactly what you are doing, don't mess around with this "tubes"!

Danny

The retractor in the '85 is an ETR, emergency tensioning retractor. The tube has a large plug inside with a cable attached. There is also a small pyrotechnic charge at the base which blows in an impact to drive the plug up the tube. This act draws the belt tight to keep you from flying forward. Once deployed the entire unit must be replaced. This ETR cannot be used on older models.

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Mike Tangas
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

'02 CLK320 Cabriolet - wifey's mid-life crisis

2012 VW Jetta Sportwagon TDI...at least its a diesel

Non illegitemae carborundum.

Wow, this is great info. So was this disposable seat belt system extended on in to the subsequent years as well? Seems like at some point it will be difficult for owners of 85's and possibly newer cars to do anything to renew their seat belt systems.

Thanks for the posts.

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1961 190Db retired
1968 220D/8 325,000
1983 300D 164,150

You can still get new units from the dealer, as well as places like FastLane/PartsShop. Plenty of viable candidates in salvage yards as well...as long as they didn't suffer a frontal collision that is.

__________________
Mike Tangas
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

'02 CLK320 Cabriolet - wifey's mid-life crisis

2012 VW Jetta Sportwagon TDI...at least its a diesel

Non illegitemae carborundum.

They make a really great bang and will smoke the cab when they go off. The conventional training is that the pyrotechnics are subject to failure at the ripe old age of 20 years.

In addition to the pyrotechnic emergency seatbelt tensioners in the 1985 300SD, are there also conventional tensioners? My 1885 300SD's seat belts have the telltale "RS" marking on the buckle, but the shoulder belt seems to lock mechanically when I pull it hard or stop suddenly. Are the pyrotechnics a secondary system designed to provide a faster response to a frontal collision? If the pyrotechnic charges are past their "expiration date," do I still have the protection of conventional tensioners in my vehicle?

They lock normally, but in an airbag collision, they also pre-tension the seatbelt.

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Gone to the dark side

- Jeff

So, even if the seatbelt pyrotechnics don't fire, I still have the regular locking mechanism to protect me in a crash? (Note: My 1985 300SD doesn't have the optional airbag but it does have pyrotechnic ETR.)

Yes.

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

That's good to know! Thanks!