W124 Headrests do not go up - PeachParts Mercedes-Benz Forum

DavidB29 · #1 01-05-2003, 07:35 PM

The headrests in my newly-acquired 300E are not working. That is, the motor does not raise the head rest. I have heard that the gears get damaged on the mechanism, and have seen several cars of this model and earlier that had similar-lookimng problems. What is the usual failure mode, and what does repair cost. Anyone know how difficult it is to do the repair?
Thanks!

Kestas · #2 01-05-2003, 09:45 PM

I did both mine a couple months ago. Failure is confined to the plastic pinion/rack gear assembly between the motor and headrest. The part is called a "headrest guide" (PN 124 970 02 26) and cost around $16.50 from Fastlane.

The difficult part of the repair is removing the seat rear cover. The first time removing the seat rear cover can be a real pain.... but doable. Everything else is easy.

95E320cab · #3 01-05-2003, 10:50 PM

Someone on this BB has submitted a detailed prcedure for this repair. I did mine last winter. Kestas is right, removing the seatback is the most difficult part; that and the structure inside is apparently manufactured by Gerber knives. I cut the heck out of my hands in there.

I salvaged the old plastic gears. Using several plastic ratcheted tie wraps, reattached it to the seat frame. Got the idea from the post.

DavidB29 · #4 01-06-2003, 09:55 PM

First of all, thanks to both of you for the inputs.
Second, Yes, I am talking about the front seats.
Third, your replies don't say, but I assume the repair can be done with the seats in the car, is that correct? The manual says to remove the seats to do a similar repair on the seats with manual crank-up headrests, and has no procedure specific to the motorized seats.
And when you say it is difficult to remove the back, do you have any suggestions or tips? It looks as if there are two screws, and then you have to release the seat back from the sides or edges, apparently by either spreading the sides or by somehow curivng the back, or some combination.
By the way, is this something not smart to do if you have a bad back?
Oh, and the $16 part -- is that one for each seat, or one for each of the two headrest posts?
Also, a friend of mine did this repair on a late-80s 560SEC and told me that he was able to repair the broken plastic piece with small hose clamps, which has worked now for several years. That sounds like what one of you is saying.
Thanks again.

Kestas · #5 01-06-2003, 10:19 PM

The repair is done with the seat in the car.

There is only one headrest guide per seat... only one post is used for powering the headrest.

I don't know how bad your back is (mine isn't perfect), but removing the seat back is more frustrating than anything. What makes removing the seatback difficult the first time is the fact that there is a lot of "sticking" between the surfaces that need to come apart. I swore that the seat back would break while I was removing mine (it didn't). One tip is to work from the bottom and have the mating surfaces roll apart. Keep tugging and pulling at either bottom corner. Once it starts moving, you're home free. I kept tugging and pulling for at least a half hour before anything happened. I just want you to be mentally prepared for this job. It'll happen.

In my case the headrest guides were broken on each seat. One had the rack broken - no shadetree fix for that, I had to buy a new assembly. On the other one, the gear housing broke. (Buy one - may as well buy the other). I didn't try, but I don't see why it can't be fixed with a hose clamp. If only the housing is broken on yours, you may get by with a no-cost fix... just your labor!

G-Benz · #6 01-06-2003, 10:27 PM

This is doable with the seats in place...just move them as forward as possible for easy access to the rear panel(s).

As you said, two screws hold the panel in place. The panel has a vertical lip on each side that fits along the same vertical groove along the seat edges. The seatback springs provide the tension needed to hold the assembly in place...so pressing down on the seat from the front will alleviate the load on the panel and make it easier to remove. It's not obvious at first, but once you've done this, you know how to go about it the next time.

Just remove one edge. You can swing the panel outward enough to gain access to the internals.

The headrest assembly is $16.50 per seat. I bought two for insurance.

Replacing the assembly is about a five-minute job. Interesting you say you can't move your headrests "up", as the usual problem is just the opposite. The plastic "clamp" fails, therefore no grip is provided to pull the headrest down, but there is usually sufficient material left to push the headrest up by inertia. I guess the clamp has self-destructed in your case.

Hope this helps...

95E320cab · #7 01-06-2003, 10:57 PM

As you can see, the hardest part of this repair is removing the seatback. Good attempts at describing above. Obviously, the seatback has to come off from the bottom up. I used a thin screwdriver to get the vertical plastic strip started out of the channel. Once you have it started, it is easy to see how it is held in place. As G-Benz said, the tension of the leather spread across the upper seat is what holds it in place. If you can, have someone squeeze one side of the seat in with both hands while you pry the plastic strip out of the bottom of the channel. Let us know how you do. There is really not much force required to pull the seatback off, so your back should be fine.

dieseldude · #8 01-06-2003, 11:27 PM

Dang, knew I should have started this project sooner!

I have electronic headrest failures in both front seats of my E420 as well.

I believe it was you G-Benz, who posted the very-good article on this awhile back. I was planning on taking digital pics of the process, and coupled with your excellent commentaty, create a DIY article for the site. This seems like a pretty common failure.

Alas, too many other projects going on to tackle this one! I'm still going to do this and use other members comments/suggestions (with due credit given of course), so let us know how it goes DavidB29!

Regards,
- Ryan

DavidB29 · #9 03-29-2003, 04:22 PM

Headrests are done.

Thanks in part to the advice I got from this site, I have just completed the replacement of the “adjusting rail” on both the headrests in my 92 300E.
The adjusting rail is the name used in the service manual for an assembly that is much like a rack and pinion. It has a toothed track or rack in which a gear unit rides up and down as you operate the headrest motor. The gear unit has a 2-piece snap fitting into which the left shaft of the headrest snaps. It is the snap fitting that broke on both my seats, thus preventing the motor from moving the headrest up and down.
Some observations:
1. As noted here, it is not too difficult to replace this part. The difficulty is to remove the panel on the seat back to get at the part, and to reinstall the panel without damage. One reason it is difficult is that it is damn near impossible to understand how it comes apart until you have it apart, unless you have seen it apart before! Even with the comments here plus the shop manual, I did not realize how the upholstery on the sides of the seat wrap around the back panel and tuck into its edges. Once you see that, it does make it easier to remove the panel. But even having done it, I find it difficult time to describe that upholstery tuck and how the rear panel fits into it.
2. As well as I can describe it, the easiest process to remove the back is as follows. Undo the two screws on the bottom, then slide the panel down about an inch, just enough for the top lip of the back panel to clear the top edge of the seat. (The back panel has a lip that slips under the lower edge of the upper edge of the seat back.) It takes a fair amount of force to move the panel, and it is difficult to find a place to grab the back panel. When I did the first seat, it took two of us to move the panel down. When I did the second one, I was able to do it alone. One way to do it, if you are careful, is to lean over the seat from the front and slide your hands into the pocket on the seat back. Press down as evenly as you can (so you do not damage the upholstery). Once there is an inch or so of clearance between the seat back and the top surface, slip one edge of the seat back out from under the tucked-in side upholstery. I have a plastic body or upholstery tool that was invaluable for this. It is essentially a tapered, thick shim (that is, not sharp enough to cut anything). Compress the seat side (a second person helps here) to reduce the tension on the upholstery. Slip the tool up under the side upholstery where it folds into the seat back’s groove, and gently but firmly lift it out. It will lift out and flip around. Work up and down from where you start. I agree with G-Benz who said that you only need to remove one edge of the panel to do the job. That makes it much easier to put the seat back together. When I did the first seat I took off the whole back, and wish I had not.
3. I wish I had taken pictures!
4. When I reinstalled the back panel, I found I could force the panel up gradually by heaving up on the bottom outer edge where the metal rails are. Use the upholstery tool to keep the side tucked in and smooth. Watch out for the side upholstery bunching up.
5. It can be a fairly demanding task on your back and neck.
6. Watch out for grease from the seat mechanism. You can get it on the upholstery if you are not careful.
7. When I opened the driver’s seat, I found evidence that the adjusting rail was replaced once before. This is discouraging, in that it indicates it breaks easily. This is one of those situations in which a complicated, expensive mechanism can be defeated by the failure of a small, inexpensive part. And the labor to replace the part is considerable, in comparison to the part’s value.
8. I suspect the trick to preventing the failure is to be very careful when removing the headrests, and never forcing them up or down manually except to remove them. Yanking up on them without releasing the latch per the owner’s manual procedure will readily damage the snap fitting at the top of the adjusting rail. When I had the mechanism apart, it was easy to see why the headrest had to be in the top position when it is removed – only there does the latch mechanism release the headrest post from the snap fitting.
Thanks again to those who make suggestions, and best wishes to others who need to do this job.

DavidB29 · #10 03-30-2003, 03:03 PM

Just in case you want a comparison to FastLane's price, my local MB dealer wanted $21.75 for the W124 headrest adjuster (P/N 124-970-01-26). My MBCA member discount knocks a couple of bucks off that.
Not sure why the part number is slightly different from that posted earlier in this thread, but this is what is on my receipt.

#11 03-30-2003, 04:18 PM

Hi,

How about some preventative measures like the how to lub the rails and with what.

Cleaning tips?

Thanks,

DavidB29 · #12 03-30-2003, 07:47 PM

The headrest mechanism did not seem to have any obvious lubricant. The parts are plastic or nylon and move very easily. Lack of lubrication was not a factor in the failures on my two seats. So I would not lubricate it. Lubrication would probably just run the risk of a mess on your upholstery and rugs.
As someone else commented earlier in the thread, try to avoid stressing the headrest mechanism by not running the motor after it reaches one end of its travel or the other, and maybe backing it off once you get there.
Personally, as I commented above, it looks to me as if the piece that I replaced breaks because of mishandling when people move the headrest manually. The sort of damage I encountered did not happen from running the motor. (It was like that when I bought the car, so I admit I am surmising.) And for that matter, try to set it where you want it and leave it. If there are multiple drivers, maybe there is not much you can do except to caution the others not to move the headrests up or down by hand, ever!
And if you are fortunate enough to have the seat position memory, use it. The headrest will move to where it is supposed to be and stop.
On the other hand, I assume other types of failures could occur.
As for the rest of the seat and its many mechanisms, I have no experience with failures so I will suggest that others comment who might be more knowledgeable in that area. But in general, i would not lubricate anything that the service manual dod not call for lubricating. You would be liely to use too much, or the wrong stuff, and/or make a mess.

Kestas · #13 03-31-2003, 09:05 AM

My old ones were lubricated. The grease was packed in the white pinion assembly as shown in Jasper's attached image.

Ditto on David's advice to avoid dwelling at the stops and to avoid manually pulling on the headrests.

From what I know about gears, there is a spreading force any time they are used. This may be the force that breaks it. For preventive measure it may pay to wrap the pinion assembly tightly once it's mounted in the seat frame with something like plastic ties. This technique has also been reported to repair some broken headrest guides.

David, your assembly book calls it "adjusting rail" (PN 124 970 01 26). My replacement part from Fastlane calls it "headrest guide" (PN 124 970 02 26). I don't know why. (Picture is shown without pinion assembly.)

DavidB29 · #14 03-31-2003, 08:14 PM

If yours broke where it is broken in the picture, it is a different failure from mine. My two broke in the latch assembly (left end as shown in your picture), not in the gear strip or rack portion.