A check before replacing 124 rear window regulators, possibly others.

hannay

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1995 S124

I have done a few of these over the years ... typically an easy swap, always straightforward, 30-60 mins depending on doorcard co-operation :).

However ...

I have just had a rear window start to struggle to get much past 3/4 closed before giving up. I keep the channels cleaned so presumed it to be a motor/cable problem unless finding gunk buildup inhibiting the teflon slider on the rail once exposed, which is very unlikely.

So with Rob Parker (thanks Rob!) standing by to send a replacement I took the doorcard off in order to double-check before sending payment, and instantly could see what the real cause of the problem was.

The three isolation mountings securing the motor-body to the inner doorskin had failed through the rubber section. The photo shows just what a state the mounts were in, no doubt it had been holding on one for a time now until that finally failed too.

This meant that although the regulator's cable track was firmly secured to the door by its top and bottom bolts, the small amount of displacement movement available at the offset motor-position when it was operating was being partly transferred and causing the alignment angle of the glass to shift just enough so that the window couldn't complete its travel without eventually binding simply from interference. Operated out of the car the regulator purrs smoothly all the way.

So if your window doesn't fully close, don't just expect it is worn and replace it, check these mounts. One clue before you even start is the glass-angle as it raises, which you can easily check visually from above - look for whether the angle of the glass seems too much at odds with the channel it is trying to rise into; another would be the lack of slipping-gear noises from the motor, suggesting that it has probably not failed through drive-wear yet.

Bear in mind that because the cable track is firmly secured top and bottom you can at first get the impression that the whole unit is pretty firm itself. The isolation mounts are tucked away because the motor is offset, but you can get to them enough to see if they have a line through them: see if operating the motor or just leaning heavily on the motor-base - not the cable track, which is where you first want to grab it but that's bolted in place and won't move anyway - makes a suspected mount failure-line open up completely or at least become more apparent.

If you are still not confident however, then just take it out anyway it is simple to do at that stage, and it will be easy to verify.

If even one of the mounts is still sound I'd expect the windows to be operating perfectly normally, so if this is actually a cause of your problem I'd expect all 3 to have failed and the fault only noticed once the last one went.

And if that's the case your fix is probably just three new mounts instead of the cost of a replacement unit whether new and worry-free or used and limited-life. Either way it is no more work really, you have to take one unit out and put one unit in - hopefully it might just be the same unit in both cases once you have replaced the mounts.

And yes I know that it is no great cost or problem just to replace the whole thing one way or another anyway, but that's SO not in the spirit of 124 maintenance! :)

I'm thinking this is likely applicable to other MB models also.

3 MB dealers have now told me there are no new 124/rear units in the UK at this time (Mar 2018 if you have come to this later) nor in Germany right now and they are backordered and awaiting estimated availability.

So I'm going to explore availability of these mounts first as they must be used elsewhere, or a suitable equivalent. I'd rather re-fit a known-good unit with new mounts, than an uncertain used unit with mounts that themselves may well also be on borrowed time by now.

So ....

In the meantime, if you have come across these in the photo or similar please let me know ... overall length is 3cm, threaded sections 7mm one side 12mm the other though longer can of course be shortened to suit. I have no idea what the thread is, but thread pitch gives 6 turns/peaks per 5mm, so 11 per cm ... thread measured across the peaks is 6mm, and across the troughs looks a shade under 5mm.


124 window reg mounts.JPG
 
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hannay

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Thanks!

Very possibly I suspect, and I'll trawl when home this evening and see what those listings might have to offer.

A couple of Motor Factors have shaken their heads muttering so far, and MB doesn't show a part number though I'm not entirely surprised for a sub-sub-sub-assembly component ...

Bound to find it as something used in the innards of a washing machine or something :)

Hmmm, "bobbins" ... would never have thought to ask by that name without being redirected to a haberdasher!
 
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hannay

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For the benefit of anyone wondering by now about suitable new mounts, or coming across this later with a similar issue, I wasn't able to get on to it for a few days but spent only a very little time on it this morning and all went fine, no problem.

Required:

The mounts needed are male-male M6 x 20mm(dia) x 10mm(depth of rubber core) anti vibration mounts, also called rubber bobbin mounts. See photo below.

From:

Lost Kiwi's earlier link shows a selection on ebay, mostly originating in China though sent out from stock in the UK. They are also readily available online and direct from manufacturers if you google Anti Vibration Mounts. If you have a place that you tend to use for odd bits and pieces from time to time you may well find them there as it seems they are used very widely for anything from mounting motors in model boats, to much heavier uses altogether. And MB window lifts :)

Type and Sizes:

There are standard, custom and specialist versions, including the hexagonal type that failed which allows it to be tightened down with a spanner/drive if called for. I couldn't find the Hex in the correct sizes, and MB couldn't supply so I used the standard unwaisted circular design as shown alongside one of the originals in the photo, which is a direct M6 x 20 x 10 replacement with the "20" now being a diameter rather than a width.

The old mounts have 7mm thread length one side and 12mm the other; replacements have same length both sides and that length varies a little from mfr. to mfr. I went with 15mm and had planned to shorten both sides to suit however the motor-body's mounting thread is deeper so takes it all and more anyway, and there's more than adequate room in the area of the door-mounting to take the extra few mm projection there without fouling anything, so in the end I didn't bother. Your choice.

Cost:

Replacement mounts for the smaller sizes range in price from around 35p to a couple of pounds, or more in stainless though there is a far smaller range. Some online suppliers have a min-order value or a small-order surcharge, and with postage the cost can run from £10 to £20 for the same three.

I simply ordered mine from the Four Candles merchant I use for odd items as he only had a handful of 20s available in 20mm and 30mm depths and no 10mm ("no demand!"). They were there for me next day, £4.26 the lot and I had ordered 6, two sets of 3 in case of a next-time.

Specification:

Same-sizes come in different performance specifications with higher/lower shear/compression strengths. Weaker/cheaper is generally rated at 3-4KG shear and around 10-16KG compression, and ranges up to generally around 20-25 shear and 60-70 compression at £2-3 though far beyond that is available from larger units.

I went with 17KG shear/38KG compression, on the basis that if the regulator muscled-up more than 20/40 KG of escape-force it totally deserved its freedom!

Fitting:

Replacement of old by new is simply a matter of unscrewing the one and screwing in the other .. the rubber section lets you grip to tighten it down very securely even without tools, though with appropriate care for its circular shape you could still get grips on the bottom-plate if you really wanted to put your shoulder in to it without risking applying shear-stresses to the core and having to reorder much sooner than expected!

One tip:

I had already removed all of the failed old mounts for the photo in the first post above.

There is of course some natural tension in the regulator mechanism as a whole, and replacing the new mounts was not a difficult process at all though just a tad awkward with motor/plate thus destabilised and therefore having to apply tension in order to align the mount-plate and motor-body holes whilst holding the motor unit and plate in one hand and the new mount in the other ready to screw it in. Anyone with two left arms/hands and one right won't get this at all and will wonder just what the problem is.

If I was doing it again it would of course now be without taking photos for here, and I would remove one old and insert one new, remove next old and replace next new, then replace the third mount .. at no time does this release the tension, and allows each new mount in turn to screw easily in to an already-aligned hole - just a few seconds each.

And from that point the complete regulator unit then fits straight back in to position inside the door, and its 5 nuts/bolts have it locked down barely a minute later.

The removal and refit steps are always very simple because they are a doddle to fit and almost jump in to place for you - as long as it is a genuine MB part! Others can require more fettling than you would care for because of the exaggerating effect of angular inaccuracies on critical but distanced locating points, and more skin than is actually covering your knuckles.

Relocating the window glass on to the regulator's lift/runner is then a 5 second operation (make sure the runner is right at the bottom of its travel or there's more resistance than you need to have to fight with!), and after refitting the securing clip (2 seconds) that part's done (check the window operates fully) and just the doorcard etc to put back ...

... which sometimes is also a drop-in-first-time operation, but other times calls for some shuffling around getting all the clips located together before engaging them with one good push - you can't do that in sections, either they all locate or you have to start over.

One doorcard-tip:

If your car doesn't have a screw-off lock button, be sure to locate it through the hole in the top-edge of the doorcard before you locate the doorcard fully in its clips.

If you don't, then the one-piece button will now be trapped under/inside the rollover top of the doorcard and you will choose to do just about anything necessary and take whatever time it needs to try and come up with a means of getting it freed and up through that hole all by itself, rather than give in and unclip the doorcard that you might just have tried 30-40-50 or more times to get all of its clips in the right places despite the doorcard no longer being flat and even, despite the water barrier having shifted just slightly but still covered enough of some locating holes that you can't even get the clips in there anyway even when they are properly all lined-up at last, and despite not quite managing the perfect co-ordination reliably every time between hands, knees, thighs and tummy (!) necessary to ensure the dead-flat configuration of doorcard which is the only way you will ever get all clips in the same relationship with their respective mounting holes, and avoid that sodding missing-out on just two of them which means it all has to come right off yet a-sodding-gain!

But you do learn after doing a few of them :)

But anyway ...

Should you find your window failing to operate fully, just check the mounts first ... it is unusual that they go like this, however in many ways that's actually preferable as you then can fix it for a couple of pounds and maybe 30-40 minutes rather than spend £35-50 on a used unit that might not last that long, or some size of gold bar for a new MB unit whenever they happen to be briefly around.

I hope that is useful to someone.

124 replacement mounts.JPG 124 rear win reg mounts.JPG
 

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