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1990 Mercedes Benz 300E
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Discussion Starter #1
Hi,

The rear height adjustment (rear tilt) for my driver's seat is binding on the console side... it also looks like the black plastic trim under the seat on the same side has worked loose... the pinion seems to be engaging on the door side cause the cushion flexes (scary)... any idea what might be wrong? Pinion gear binding on one side? Is there only 1 motor that controls this axis?

Tks,
 

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1990 Mercedes Benz 300E
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1,336 Posts
Discussion Starter #2
ok, so I unbolted the seat from the chassis (not fun as I had to assist the frozen tilt mechanism to get at the last bolt).

So I noted a few things (also took some picts for reference)...

1. The gearbox? for this tilt movement appears to be driven by a cable coming from a motor mounted under the seat. The tilt feature works on the door side but not on the console side.

2. There is what I can only describe as a "tinny sound" something like a fire buzzer coming from the gearbox on the dead side when I actuate the tilt movement.

3. I can get the movement to work if I pull up on the mechanism gear which is attatched to the drive gear with a bent wire tool (there is an eye hole on the mechanism gear) but when the action reaches its limit (going up) it freezes up again.

4. It looks like there are 4 torx screws holding a plate onto the particular gearbox in question. If I remove the torx screws will I get access to the gears in the box? Are they mostly nylon gears or are there metal drive gears in there? Brass? Steel?

5. Is there some sort of clutch mechanism that disengages with load that I should be looking at? Its seems possible although maybe a little overkill in this application. Still, with Mercedes engineering you never can tell.

The body of the tilt gearbox is long and one piece for both fore and aft tilt... I hope I don't have to replace the whole unit. Anyone know if I can just replace one faulty gear? (From how it sounds I would gather there is either a loose gear (spacers fell out), stripped metal gear, or stripped nylon gear gumming things up).

Helfen Sie bitte
 

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1990 Mercedes Benz 300E
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1,336 Posts
Discussion Starter #3
Ok,

Solved it... anyone with a similar problem can probably use these images as a guide.

The problem was some play had developed between the worm gear and the metal drive cable which led to the cable spinning in the bore of the worm gear. This is after the drive cable is fed through the memory seat position sensor (acts like a clearance element as well), and fastened to the gearbox via an L-shaped black metal bracket.

I suspect that this play developed as a result of a broken retainer clip for one of the bushings that might have resulted in some play @ the bushings... translating to vibrations when the worm gear is moving. Over an indefinite period this play got to the point where the worm gear would only be actuated when spinning counterclockwise (pulling force) vs clockwise (pushing force hence pushing the cable out of the gear).

So I think by replacing the worm gear, the cable, and the broken bushing retainer that should square things up with this latest problem.

Ah, the pleasures of owning a w124 never end!
 

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1988 300E, 2006 E350 wagon
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278 Posts
necro,
I will be watching this thread closely. The exact same problem surfaced for me about a month ago. When I would adjust the rear tilt only the left side would move up or down. Since then I have just kept it so that the seat is level left to right.
I have had no time to deal with it, but later this winter i plan to put heated seats in my 1988 300E. Depending on what I find with my seat adjustment motor I may just swap in the one from the donor seats that I have for the heating elements.
Where will you get replacement gears?
 

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1990 Mercedes Benz 300E
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1,336 Posts
Discussion Starter #5
necro,
I will be watching this thread closely. The exact same problem surfaced for me about a month ago. When I would adjust the rear tilt only the left side would move up or down. Since then I have just kept it so that the seat is level left to right.
I have had no time to deal with it, but later this winter i plan to put heated seats in my 1988 300E. Depending on what I find with my seat adjustment motor I may just swap in the one from the donor seats that I have for the heating elements.
Where will you get replacement gears?
One motor operates both sides so it looks like the motor shaft is direct pinion drive on the other side and the same motor turns the cable to drive the faulty side. The cable and cable sheath are separated so you can remove the cable from the assembly by unscrewing the seat position sensor from it. The cable appears to be made of wound steel with asymmetrically tapered ends (you can't just reverse the direction of the cable if one end is frayed).

I think the only parts I'll need are a new cable, a new worm gear, and a replacement clip (for the bushing). I'm hoping that anything assembled with torx screws, or other removable fasteners can be had as single items @ my local MB dealership.
 

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1990 Mercedes Benz 300E
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Discussion Starter #6
So I was able to make it out to my MB dealer for spare parts which leads me to a modification for fixing the problem.

MB will not sell the worm gear or clip separately (no exploded view of the tilt/slide mechanism gearbox) and they want $690 for a new gearbox. That was my Thksgiving suprise. So this is what I'm going to do.

Essentially, the problem lies with the excessive free-play between the worm gear mating bore and the cable shaft. I cleaned up the worm gear as much as possible with degreaser and looked into the bore. Basically, I can see the start of some wear in the form of "shallow scalloped metal" 45 degrees from the right angles of the bore... a product of the worm gear free-spinning in the bore for several days.

My strategy now is to use JB Weld to tighten those tolerances in the bore... basically I'll be adding some more metal in there. Hopefully it will be easy to undo in the future (worm gear bore is smooth, cable is finely textured) if I have to replace the cable shaft assembly sometime down the road.

My other option would be to replace the shaft (and guide tube) but getting to the guide tube is a massive undertaking. All 4 motors appear to be fastened to a common bracket and the only way to remove the proper motor (so you can remove the C-clip retaining ring on the cable guide) is to first remove the cable from the other side, unscrew the motor (requires LOTS of patience), and drop the motor to access the C-clip hiding behind the bracket aperture for the guide tube.

It might come down to this (hope not) but I'll see what my JB Weld "band-aid" can accomplish first. If it works for a few years its that much less headache I have for fixing complicated luxury car pop/whirr/wizz gizmos.
 

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1990 Mercedes Benz 300E
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Discussion Starter #7
So I've done the repair but will wait a few days for the epoxy to properly cure before testing it out.

Some other things:

You have to account for the slop that was originally present between the gear bore and the cable so the best way to do this is to reassemble the gearbox (with epoxied cable) while the epoxy is still setting. The relationship between the memory seat sensor and the worm gear is held true by doing this and it should alleviate any fears that the gear "sagged" in the epoxy and isn't spinning true.

I did not re-pack the gearbox with grease but I'll do that after I've verified the repair works. Its not a big deal since it'll be a few days in this cool weather before I test out the integrity of the new fitting. When you are torquing the torx screws take extra care you don't strip the heads... otherwise you will be searching for a replacement fastener since MB doesn't sell any component of the tilt gearbox on its own... you don't want to be stuck with a $690 part or waiting around for some other guy to sell you an old part if it can be avoided. I still have to figure out how to salvage that small bushing retainer clip... maybe I'll just secure it in place with a tiny dab of RTF or gorilla glue. Doesn't look like it moved much so it might be ok to re-use it without modification.

I also had the option of replacing the whole cable assembly (cable shaft + guide tube) but changed my mind once I realized what a horrendous task it would be. Changing the cable is no big deal (since it can be easily extracted from the guide tube) but changing the guide tube looks really hellish since all the motors share a common bracket and you have to at least remove both drive cables for the rear tilt feature (one/ each side of the motor) before you can drop the motor from its flanking brackets. Even then, you will probably need to finesse some small hex sockets or wrenches in a confined space... I can see how changing out an entire cable assembly can be many hundreds of dollars in tedious labor even at a competent indie!
 

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Cruise Control
'87 300TD/'90 300D/'94 Quattro/'89 Vanagon TDI/'01 EV Weekender VR6
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Nice write-up. I think this should go in the upcoming DIY section.
 

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1990 Mercedes Benz 300E
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1,336 Posts
Discussion Starter #9
One last point.

The purpose of using JB Weld is as a filler to fill the empty space between the cable and the worm gear bore. Since it would be highly disadvantageous to actually bond the two together (if you have to replace the cable one day for other reasons) it stands to reason that you don't want the two mating materials bonded.

For this reason, I purposefully cleaned both the cable end and the worm gear with a petroleum-based distillate and left a very thin film of petroleum distillate on the surfaces. Hopefully, this will prevent bonding of the cable and worm gear but the minute amounts of surface contaminants will not interfere with the curing process. As long as there is negligible clearance between the cable and bore, and the material used as a filler is non-compressible and strong, then I'll have the best of both worlds... smooth function, and the flexibility of it being reversible sometime down the road.
 

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1990 Mercedes Benz 300E
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Discussion Starter #10
last images...

I tried it out and the JB Weld strategy appears to have worked. I'm not sure for how long though.... hopefully it will last a few years before it goes again.

Just a few more considerations when finishing the job.

The hinge mechanisms for the left and right side are fully independent of each other so you have to re-align them before you close up the gearbox. So long as the worm gear is disengaged from the nylon reduction gear the hinge can be freely articulated. What I did was set the front movement to the lowest setting, then set the rear movement on the lowest setting while fully collapsing the faulty side (before re-assembly). Since the hinge mechanisms for fore and aft can affect each other's respective geometries its good to have both movements at their respective end-movements as a reference.

Packing the assembly with grease is a good idea as the factory grease is now about 20 yrs old and looks more like candle wax. I used the MB factory grease (used for lubricating the sunroof rails... but MB also specs it for other light duty purposes as well like the windshield wiper movement) but I'm sure any other general grease will suffice... I had the MB lying around and its probably what the factory used on the production line so I'm more comfortable with compatibility... some greases are not compatible so if you want to use something and your not sure then you might have to degrease the entire assembly before packing it again (NO THANKS!). Its not like the power seats are in constant use (especially the rear tilt) so I'm sure its not super critical. Its probably more important that the grease does not attract dirt and will not dry over time.

Before finishing the job its now a good time to clean house and recover various do-dads that fell in between the driver's seat and the console over the years. I found a treasure trove of coins (mostly pennies, nickles, and dimes) that date back to the early 80s! I also saw some offending stains down there... probably the product of someone using the center console area as a coffee stand.... most of these stains came out with Multi 7 (a stain remover). A good vacuum and things are fresh-as-new-tidy once again.

Putting the seats back: Make sure you engage both guide brackets on the console side of the seat to the guide rail. The seat is held down by 4 10mm hex bolts... access to these bolts is not so good towards the rear where the seat frame sits at an angle. It really helps if you have a U-joint and extension for your ratchet when doing up the left rear bolt. I found that the easiest sequence is to get the right rear in, then left rear, then right front, and left front. You want to start the bolts that have the hardest access. There are 2 separate metal pressure plates at the rear that complicate things too...

You have to replace 3 pieces of trim (that I neglected to mention)... the front bolt trim, and a side piece just under the left side (to access the rear left bolt). Go gentle and slow and take your time... the way they go in is pretty intuitive.

I hope the JB Weld lives up to its reputation! If so, that would be my first 20 cent repair.
 

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2008 R500 5.5 l.
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Great job and explanations, thank you!

My R500 is experiencing the same symptom (only one side moving), although from a different origin: from what I could see, the worm gear is totally fine, it is the cable that got damaged (not bore). Many threads of the cable came out, and now it won't fit back to place. Mercedes won't sell just the cable, they only propose the full set with the motor. So I'm up to trying to fix it myself.

Anyone with a suggestion? My initial idea was to remove the extra threads to make it thin enough to fit again inside the worm gear, and then glue them all together. But thinning the cable might render it weak and the glueing business is also not so great for reasons already mentioned above.

Thank you.
 

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1983 300SD, 1986 560SEL, 1992 300D, 1995 E320 Wagon
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214 Posts
Here is how I did mine when the cables wouldn't engage the motors anymore:

 

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1992 300E 2.6
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54 Posts
My 300E has the same problem, I got my hands on a few gearboxes and motors. I'm going to take what I need from them and if there's anything left I have no problem with selling to those that may need. That being said, I do not even know if what I bought is functional-however they seem to be.
 
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