W124 Coupe Newbie - Seat Belt Presenter Diagnosis

[CreosoteChris]

Intro

Hello MBClub.co.uk forum readers – new owner here – I’ve recently acquired a red ’93 220CE, and I *totally adore* it – I actually think it’s my favourite car I’ve ever owned. First time in many years that I’ve bought a car with my heart rather than my head, and I feel like I’m 30 again. I think it’s just fabulous gliding around in my super-elegant retro-chic Merc – I just know I’ve got the coolest vehicle on the road, hands down.

Anyway, the vehicle overall is VGC, and I’m trying to get it to the spec I want, going through the interior, installing a decent stereo (making progress there)….. and my biggest issue – fixing the non-functional driver’s-side seat belt presenter. I’m a half-reasonable home mechanic/tinkerer, kinda looking for some guidance as to where to take the diagnosis from here.

I’ve had a good read of the threads here and elsewhere discussing this subject, and done some disassembly and basic diagnosis – summary as follows:

Symptoms

- Driver’s-side SBP does not operate as expected when door closed
- No whirring noises or other signs of activity

Procedure

1. Swapped door switches (lower door switched used by SBP circuit): Driver’s-side ó Passenger-side
=> Passenger-side stays working, driver’s-side stays inoperative) – NOT DOOR SWITCHES

2. Tried the following: engine running - open driver’s door – close driver’s door - physically pull the extender towards extended position
=> Motorised retraction effort can be felt, resisting the manual effort to extend the SBP arm – POSSIBLE SBP UNIT POSITION-SENSING MICROSWITCH ISSUE (SBP thinks it’s in the extended position even when retracted)
=> See http://www.benzworld.org/forums/w124-e-ce-d-td-class/1504310-230-ce-seat-belt-extender-does.html

3. Uninstalled the complete driver’s-side SBP from the car body
NOTE - the presenter arm can be moved along the track – extending it takes a considerable effort, retracting it a lot less. There is one tooth missing from the nylon cogs that actuate the arm, but the mechanism still seem to run smoothly.

4. Swapped control box units (the Bosch-branded plastic box attached by two screws to rear of SBP assembly): Driver’s-side ó Passenger-side
=> Passenger-side stays working, driver’s-side stays inoperative) – NOT SBP CONTROL BOXES

5. Tried connecting loose driver’s-side SBP to passenger-side harness connector
=> Driver’s assembly connected to passenger-side harness does not operate – SUGGESTS A FAULT WITH THE DRIVER’S SBP ASSEMBLY* Additionally, someone has clearly tried and failed to fix this before, evidence of trim disassembly, attempt to prise open the working control box now sitting on the passenger side – so I wasn’t honestly expecting this to give me a result.
=> Also corroborates (2) above.

*However, I’m not really fully convinced that the driver’s SBP should work when connected to the passenger SBP harness Molex connector, without being properly earthed by fitment to the vehicle chassis.

At this point, I was going to remove the trim piece covering the passenger-side SBP, and try actuating the known-good passenger-side SBP assembly, connected to the driver’s-side harness. However, the trim really doesn’t want to come off, and I am reluctant to exert any more force than I’ve already tried (just for diagnosis, rather than actual fix) for fear of breaking something, and not really getting me closer to a fix.

Looking at the removed SBP assembly (arm completely out) I don’t really understand clearly how the position-sensing is taking place – I’ve seen threads mentioning four microswitches, but I’m not really clear about how to locate or check them. Also wondering if some more experienced / resourceful readers of this forum might be able to advise, or suggest otherwise how I proceed to root cause diagnosis / fix here. These units are obviously sought-after items and now fetch hefty prices - I think that if really necessary I’ll stump up, but reluctant to do so until I’ve explored the fix-it possibilities more thoroughly.

Any advice appreciated

Regards Chris, Manchester

 

[Sp!ke]

I know it sounds daft but have you checked the fuse? Sometimes the fuse gets corrosion on the ends and need a bit of a clean before re-seating it.

A common problem with the seat belt presenters... (and other items on a W124)

 

[WDB124066]

Here are some photos of the micro switches on the presenter unit itself. There appear to be three; in, out & overload by the looks...??

Three wires to each switch and a bridge between them, on the in & out micros, and a simple two wires to the overload micro.

What trim is not cooperating?

 

[CreosoteChris]

OK, thanks for the responses:

Spike - pretty sure it's not fuse - there is definitely power to the unit, this was clear from trying to manually pull the presenter to the extended position (it actively resisted in a motorised way).

WDB124066 - thanks for the pix - I was just too dumb and / or timid to remove the black cover over the microswitches.

Anyway, got that cover off, slid out the bigger dual-switch, and one of the little yellow switch tabs appears to be stuck, is not coming out of the pushed-in position properly. Looks very likely to be my issue (I'll be so proud of myself if I actually solve this....)

Just need to figure out how to fix that without breaking it, will do so in the morning proper (writing this whilst on an overnight call-out for work)


Cheers!

Chris

 

[WDB124066]

Wouldn't it be a peach if those were still offered my MB or Bosch, bet they are if only you had a number for it.

Anyway as you say for better off investigating on the kitchen table after the bacon and eggs have been cleared away than in the middle of the night on the end of a Bourbon for example...

 

[kth286]

Chris

I like your process thus far, and eager to hear feedback on a successful conclusion.

That car seems in good hands.

 

[CreosoteChris]

OK, I’ve taken a close look, and poked the switch actuator a bit. From the appearance, and feel of the way the switch moves (it seems like the actuator button doesn’t have the right amount of travel, or move as freely as it should), looks like the button has worn away with extended use. I was hoping that there was some grit in there preventing free movement, but I’m no longer hopeful of that.

The switch is branded Cherry, and is stamped with lettering:
0.1A 125 VAC E63

It appears to be of a type no longer available, and I think that fixing-by-disassembly is pretty unlikely to be feasible:
Cherry product page
http://www.cherrycorp.com/english/switches/submini/e_mod.htm
Cherry schematic
http://www.cherrycorp.com/english/switches/submini/images/e61_cutaway_2x.gi
Out of Stock page – Well Gain Electronics
http://www.wellgainelectronics.com/cherrye63greensnapbutton.aspx


Considering my next step – it sure would be handy to get hold of a junked assembly to cannibalise for bits . The symptoms I have are a very good match for the evidence I’m seeing on the microswitch, so I’m pretty confident I could make it work with the right part – if anyone here has replaced an SBP unit, I’m certainly interested in the broken one that's been pulled out.


Will advise on any further developments – thanks for the advice and encouragement!

Regards, Chris

 

[tintinmt]

Did you check the underside of the arm (rack) for wear?
You should be able to source a presenter mechanism from a breaker - I think the other coupés of the period share the same mechanism. The cabriolet has a unique one.

 

[CreosoteChris]

Really close to a fix now……

….I continued fiddling with the dud microswitch, running a pin down the gap between the moving plastic actuator and the switch body – eventually the actuator popped out into the correct position. However, the edges weren’t as smooth as the other two switch buttons / actuators, so I dressed it a little with a nail file until it seemed to be working (ish), and reassembled. Installed in the car, it worked……

…..about 4 or 5 times, before giving up the ghost again. Luckily, I didn’t reassemble the whole rear driver’s-side interior around it, so pulling it again will be a 5-minute job. Reckon that with a bit more fiddling and filing + trial-and-error fitting of the switch in the exact optimum position, I’ve got a good chance of getting it working reliably (and in the meantime I’ll keep an eye out for a junker I can rip apart for a better-condition switch).

Anyway, I’ve proved 100% that the microswitch was causing my SBP dysfunction, and know for a fact that it can be (and will be) properly fixed.

Will update with the final outcome – thanks to the MBClub UK community!

Chris, ’93 220CE, red / black leather, Manchester

 

[WDB124066]

Can you build the button up with dobs of plastic cement and maybe a tiny piece of suitably trimmed plastic...

Or maybe swap the switch for the passengers side one and carry on till you find a replacement.

 

[CreosoteChris]

Hi WDB124066

I’ve made another attempt at rendering the dodgy microswitch useable – it now seems less prone to sticking in the pushed-in position (though it doesn’t have the positive-feeling springiness of a good one). I think it may be possible, by carefully paying attention to the positioning with respect to the bumps on the sliding arm, to make sure it doesn’t get pushed far enough in to stick again. Gonna see how that goes tomorrow morning - hopefully I won’t get any “red-eye” call-outs from work tonight.

As for the other suggestions

- Not keen on going anywhere near the button with an open tube of glue or similar – I’ve never been good at that sort of thing, and one dribble down the side is likely to be curtains for that microswitch. And I no longer think , as I previously did, that the button is really worn down - I was fooled by it being trapped in the pushed-in position.

- I did, at one stage of the diagnosis, attempt to remove the big trim section next to the passenger seat, and failed to get it off – seems like that piece has been in place for 21 years since the car left the factory. And then I’d be doing two lots of soldering (another of my less-than-strong suits). Don’t feel the benefits are compelling enough to make this worth pursuing.

If I end up driving with a non-functional driver’s side SBP for a while whist I locate a (hopefully broken) spare that’s not priced in the stratosphere, I can live with that. I’m not a great mechanic, so actually I’m very pleased to have tracked this down to a certain diagnosis, it’s a big success for me…….

…..and I have other stuff to keep me occupied, want to run the cabling for my CD changer, I’m trying to construct a discreet-but-sophisticated stereo setup, in keeping with the general age and tenor of the vehicle (minidisc head unit + boot-mount CD changer - keepin’ it ‘90s!)


Thanks for your continued interest, I appreciate it.

Chris

 

[CreosoteChris]

SOLVED.

For anyone interested – this is now fixed, the SBP is reinstalled in the car, and has now been working faultlessly for several days

The microswitches are held onto the SBP unit by two screws that locate in slots on the holding rail – so the precise positioning of the switches with respect to the sliding rail is variable by a few mm. This results in a “Goldilocks” effect.

- First rebuild attempt - TOO LOW – switches too close to rail, the problem switch got pushed in too far, and stuck (SBP stops working completely)

- Second attempt - TOO HIGH – switches not close enough to rail, one switch never got pushed in far enough. (SBP extends but doesn’t stop at the fully-extended position)

- Third attempt – JUST RIGHT – works A-OK

Hope this helps someone in due course – thanks for all the interest & responses

Chris

 

[WDB124066]

Did you get a picture by any chance...?

 

[CreosoteChris]

I did some pics at one point in the procedure - on my work PC right now, I'll take a look this evening to see if I have anything that illustrates this

Chris

 

[grober]

http://media.digikey.com/pdf/PCNs/Cherry/PCN_E61toE64_2_EOL.pdf

http://cherryswitches.com/wp-content/blogs.dir/7/2012/07/subminiature_switch_DC_EN1.pdf

 

[1001ab]

Great thread.
I have an intermittently non-compliant SBP on the driver's side and have a couple of spare SBPs but I've never gotten around to having a look.
I think I'll print this thread out and have a go now that CreosoteChris has done the hard work...

 

[jaymanek]

Excellent... I would have been on ebay for a replacement ages ago! Well done for persevering.

 

[CreosoteChris]

Further to WDB124066's request, I checked my pics.......

....unfortunately they were abysmal quality - seems that I reached the close-distance focus limits of the camera.

The attached shows out-of-focus microswitch pair unscrewed from the rail, and in the background the slots that provide latitude for up/down adjustment

Anyway, glad that other forums readers seem to be getting a benefit from the thread.

Chris

 

[WDB124066]

I see now, that makes sense.

And yes nice we fix for what looks like could be quite a common problem.

I'm sitting here thinking if I should try and get some of the last Cherry switches for spares, or figure out if their replacement switch will be good to go in our application.
In any case I have some spare arms from a Coupe and I figure I can rob the switches and gear wheels when needed.

If only I could find some post 93 leather seat heating elements of even covers with elements in them. The list of tricky to find 124 parts grows....

 

[RonBelz]

Hi WDB124066

I’ve made another attempt at rendering the dodgy microswitch useable – it now seems less prone to sticking in the pushed-in position (though it doesn’t have the positive-feeling springiness of a good one). I think it may be possible, by carefully paying attention to the positioning with respect to the bumps on the sliding arm, to make sure it doesn’t get pushed far enough in to stick again. Gonna see how that goes tomorrow morning - hopefully I won’t get any “red-eye” call-outs from work tonight.

As for the other suggestions

- Not keen on going anywhere near the button with an open tube of glue or similar – I’ve never been good at that sort of thing, and one dribble down the side is likely to be curtains for that microswitch. And I no longer think , as I previously did, that the button is really worn down - I was fooled by it being trapped in the pushed-in position.

- I did, at one stage of the diagnosis, attempt to remove the big trim section next to the passenger seat, and failed to get it off – seems like that piece has been in place for 21 years since the car left the factory. And then I’d be doing two lots of soldering (another of my less-than-strong suits). Don’t feel the benefits are compelling enough to make this worth pursuing.

If I end up driving with a non-functional driver’s side SBP for a while whist I locate a (hopefully broken) spare that’s not priced in the stratosphere, I can live with that. I’m not a great mechanic, so actually I’m very pleased to have tracked this down to a certain diagnosis, it’s a big success for me…….

…..and I have other stuff to keep me occupied, want to run the cabling for my CD changer, I’m trying to construct a discreet-but-sophisticated stereo setup, in keeping with the general age and tenor of the vehicle (minidisc head unit + boot-mount CD changer - keepin’ it ‘90s!)


Thanks for your continued interest, I appreciate it.

Chris

I hope someone is still monitoring this chain.

i have 94 W124 Cab. Both presenters terms stop working, not at same time.

i did clean up and re-grease motors. They work when powered from external battery.

the driver side presenter will not stop when the upper micro switch is depressed by the bump on the rail.

are there supposed to be two separate bumps on that rail, one for each of the two stacked micro-switches. I don’t see how that would work since the lower switch is too low for it to ever come in contact with it.

Thanks in advance for any clues.