replacing seatbelts after airbag deployment in a '89 560SEL (W126)
 

Hello,

I was in a low speed collision with my 89 560 SEL and only the passenger airbag deployed, although no one was sitting in it. My insurance would not cover the damage and declared it a total loss. So now i am currently repairing my beloved car with the insurance money i received for the value of the car. It has been almost 7 weeks since the accident and the car has been fully repaired with the exception of a few problems. Mainly to do with the airbag system. My mechanic had originally replaced the airbag with a used one, but the SRS light on the dash woulden't go off. So then my mechanic thought he needed a new airbag because he believed the used airbag wasn't "compatible" with a californian car, so he bought a new airbag, but the SRS light still stayed on. Also, the drivers side seatbelt is locked and won't retract. He has taken the car in for testing, and he has told me that the SRS module reports "only" a code 10, no others. Since the accident, I've decided that i no longer want to use airbags in the car. I find they're more trouble than their worth (in this car anyways).

What i would like to do is fix the seatbelt while keeping the SRS system disabled, by having the SRS control module removed.

My question is can i fix the seatbelt by simply replacing them with new or used seatbelts, and can i do this with the SRS system disabled? do the seatbelts rely on the SRS system to function? will they lockup without SRS?

Also, if i decide that i want a working airbag system. Would simply replacing the airbag and srs control module unlock the seatbelts? or would i have to replace the seatbelts too.


PS: I had orginally written much longer and detailed post, but i didn't want it to be too unnessarily complicated, so i shorted it. So please feel free to ask if you want to know any other info about what was damaged, replaced, etc.


Thank you for your expertise,
Drew

'89 is a little newer than my '86 so there are some changes. That being said, you probably need to replace the crash sensor (mounted to the tranny hump directly below the stereo) as they are, at least for '86, a one time use item. You also need to replace the ETR's, also probably both sides. The ETR's are the emergency tensioner for the seat belt, requires completely replacing the belt retractor assemblies in the "B" pillar. To access the crash sensor you'll have to basically gut the center console.

Yes, the airbags and crash sensor are a set. Your mechanic should have gotten a complete used setup. Don't beat him up to badly, because this is sort of an obscure fact. I believe the retractors in your car will still work after replacing the above items. I have seen this on an 87 300E.

Peter

On the '86 once the ETR's blew their charge they were through. There is a small pyrotechnic charge that drives a piston up a tube, pulling the retractor cable. Once blown there is no way to return the piston and cable and no more charge to drive the piston a second time.

Thanks for the responses.

I'm still confused though. Only the drivers side seatbelt is locked, as it was the only one in use when i had the accident. So why would i need to replace both front seat belts. Can't i simply replace the drivers side seatbelt assembly and have the seatbelt working again, or do i need the srs system working too. I do not want the srs system fixed at all, unless it has to be. I only want my seatbelts working.

I should also note that i don't think my mechanic really knows how to fix this problem. He told me he is searching for a used srs module, but does not know when/if he will find it or whether it will fix the seatbelt problem. And it doesn't seem like he's in any hurry to fix the seatbelt problem. He just seems to be trying different things, hoping each try will fix the seatbelt and srs light problem. He also doesn't seem to care how much extra all this fooling around will cost me.

So far he's already charged me an extra $1000, $1900 total on a new airbag because he thought that would fix the srs problem. He said it didn't work because the airbag was "incompatible" with a californian car. It is pretty clear to me that he doesn't how to repair the car, and is wasting my time and money trying to figure it out.

What i'm trying to do is get some solid answers as to what can and can't be done with trying to solve these issues, so that i can tell him exactly what i want done to fix the car.


Drew

All you need is a good salvage yard. A new crash sensor is something on the order of $2500, you can snag a used one from a salvage yard for pennies on the dollar. Just find a same model car that has not been in a front end crash and I'll bet the sensor is good to go. If the used one rattles it is likely spent. Ditto on the seat belts. You can grab a pair from a car that hasn't been front end wrecked - easy check is if the belts retract when you pull them down then the ETR hasn't blown. If you only need one, there is nothing wrong with grabbing a spare passengerside belt...you might just find it is blown too. The SRS light will not go off until the system is returned to serviceable condition, or until the bulb burns out.

Why wouldn't you want the added safety layer of air bags?

Mike,

It sounds like you have done some reading on this. I am not up to speed on this issue and frankly haven't had a need. I think the mechanic involved should do some research if he is truly a professional mechanic and not one of those guys who got a box of tools and has been fixen on cars for many years. Professional mechanics spend many hours and sometimes a fair amount of money on continuing education just like in any other profession. All I know about SRS problems is when someone I know crashed his 87 300E and decided to repair it. He bought another car with a frozen engine and had the body shop swap parts. They used the air bag from the doner car, but the SRS light stayed on. He then installed the crash sensor and the light went out. He did not change the seatbelts, and they appear to be working. Are you saying they shouldn't be moveable? Like I sad, Mike, it has not been an issue I have had to deal with, but if I had I would have done my research. By the way you seem to be skipping around the country these days. We used to be neighbors. I grew up in Santa Rosa, and live just over the hill from Napa Valley.

Eva or Drew or Whoever,

I think you need to change mechanics. I don't know why you chose as you did. I don't know if you chose for convenience, recommendation, or price. If it is convenience or price, you have to ask yourself a question. If I had cancer would I use the same criteria? Sometimes the most expensive repair facility can be the cheapest if they know what they are doing. That being said, you may take a look at taking the seatbelt setup out of an earlier 126 chassis to give you the seatbelt protection without all the airbag fuss. I believe the seatbelt system out of say a 380SEL or 300SD should work. I don't want to be exposed to any law suits since I live in a highly litigious state. I am meerly stating that is possible to go back to a pre air bag era. Personally I am a very defensive driver, and my chances of being in an accident are small. First of all I avoid the knats. Those are the drivers who don't know each other but drive in groups. I always stay in the open and in a lane with an out. That has saved me twice. Once I saw brake lights coming on like lighting a Christmas tree. I quickly steered into the divider strip and watched the car that was behind me slam into the car that was in front of me. Another time in dense fog I stayed in a lane with a shoulder. At the sound of crashes ahead and the sight of bright red brake lights immediatly in front, I pulled onto the shoulder and stopped. I could hear crashes for about a mile at a rhythmic pace. Most drivers don't have a clue that they are at the control of a one to two ton progectile traveling at tremendous speeds. Anyway, enough rambling and hope I have provided some food for thought.

Peter

The seat belts are still usable once the ETR has blown, they just don't retract cleanly and will hang loose. I had to do a bit of learning about the early SRS system when I got the 560SEL. It had thrown the driveshaft, which then tore through the hump inflicting a direct hit to the crash sensor. That hit deployed the air bag and blew both ETRs.

At the time I started the repairs I replaced the bag and sensor, still had a steady SRS light. Then I replaced the slip rings as they were worn and I figured the conatcts weren't touching the ring. No joy. Discussions with Steve Brotherton and a lot of reading on the system in the manual pointed me to the ETRs. I pulled a pair out of a junked 560 that was a rear hit, pistons were at the bottom of the tube indicating there were good. Installed them in my car and the light went out as the system was again whole.

When I first pulled the blown ETR's I tried to restore the retractability by driving the piston back down the tube. Couldn't move it. Then I tried disassembling the retractor...been there done that and for those who might want to try...DON'T. The mainspring is long, thin and very sharp, it tends to come out of the housing unexpectedly and fast. You could get hurt!

As for retrofitting an older style seatbelt it may not be that easy. Pre-air bag MB's did have ETR's, I think as early as '82. They used a different style retractor and right now I can't recall what drove the retractor in an accident. Due to the different systems they may very well be incompatable. The manual has a good section on the different passive restraint systems.

And yes Peter, I am bouncing around a little right now. Family is still on the west coast while I'm working in the north. Racking up lots of flyer miles though.

Thanks for the helpul info Mike.

Since this car has been branded as a 'salvaged' vehilcle I need to get it tested for a structural test. I spoke to a different mechanic who will do the structural test and told him my story. He advised me that i infact do need a working srs system to get the certificate. So now, whether I want to or not I must get this system working again, along with the seatbelts. He also said that i was overcharged a couple thousand for the work was done to the car. I plan to speak to my mechanic about how to go about repairing the srs, as well as try and negotiate a way for him to pay for some or all the extra parts i need(seatbelts, srs control module, etc). He assured me before he started fixing the car that there would be no surprise costs and that he would completely repair the car for our agreed price.

So before I talk to him next week i'd like to have my facts straight as to will probably need to be done.

Mike: You said that you "replaced the bag and sensor". By 'sensor' did you mean the srs module? or did you not need to replace this. And if i understand correctly, you did not need to replace the entire seatbelt assembly, but only the blown ETRs?

One more thing. Is is typical for SRS control modules to be replaced after every accident, in all brands of cars, or is this mainly done by Mercedes-Benz? I'm asking because my mechanic is currently charging me all these extras: srs module, seatbelts, anything that may come after. He's is not repairing the car on the agreed price. Since he doesn't seem like he works on many older style MB cars, I want to know if he should have known he had to replace the module and other things before he started working on the car. Would these repairs have been unexpected?

Thanks again very much for your help guys,
Drew

ps: 'eva' is a fond memory i use as an alias. Andrew is my real name. Also, i will try to post pictures of the damage, so you have a better idea of what i'm talking about.

I replaced the bag because it had deployed. I replaced the crash sensor, mounted on the tranny hump, because the bag deployed and the only way the bag goes pop is if the sensor activates (and remember, they are a one time use item). If you mean the SRS module that is located in the passenger side foot well, the one the crash sensor plugs in to, no I did not replace that.

When you replace the ETR's that will entail replacing the seat belt, at least the portion that crosses the body, you shouldn't have to replace the latch unless they are bad too (sometimes a bad latch can trigger the light on some models newer than my '86).

As far as replacing the sensor on other cars...well I don't know. I imagine most of the sensors are single use items. I do know that on newer models than mine there is a two stage sensor where an impact can be bad enough to trigger the ETR but not bad enough to pop the bag(s). Plus on some if the impact is great enough the passenger side bag will deploy even though no one was sitting there.

Mike,

Thanks for the lesson. If I do run into this in the future, I will have a heads up.

Peter

Thanks Mike. This is very helpful information.

Drew