W126 power seat problem - smoke!! - PeachParts Mercedes-Benz Forum

LandYaghtLover · #1 11-23-2011, 12:18 PM

Just wanted to run this past everyone. The passenger seat has had issues from day one. Right now the seat back will recline and got forward. I think it will also raise and lower.

But the headrest does not work and if the seat base is told to go backwards, it will not. But it will go forwards.

When I take the module apart I can find the fault and fix it. Then it goes back, but only if I make it do so in small increments. If I hold the switch, it may go back for about a second, then stop. Then I get lots of smoke and the circuit board trace is melted.

Any clue where to start? Could it be the motor? Tracks are clean and lubricated.

Hit Man X · #2 11-23-2011, 02:33 PM

Check the switch on the door, mine have caused me grief in the past.

LandYaghtLover · #3 11-23-2011, 03:11 PM

Quote:

Originally Posted by Hit Man X

Check the switch on the door, mine have caused me grief in the past.

I actually "rebuilt" them. Same issue(s) (memory seating is also dead, but that is an old thread and I still have to figure that one out).

It would seem the motor is drawing too much amperage. But it moves fine when it does work. I hate to get another module, just to blow that one apart too.

compress ignite · #4 11-23-2011, 07:35 PM

Is there any Lubricant "Recommended" for the Seat Tracks?
AND the Toothed "Rack and Pinion" type Rotary to Longitudinal transfer Mechanism.
Some of the Mercedes Seats use a Rotary Cable (In a sheath) for Seat motive
power. After 20+ Years without lube...

I'd almost suggest a Dry Lube Film,if nothing else is specified.
[Like is used on Sail Tracks and Zippers in Marine Use.]

CRC MARINE Lube at West Marine

LandYaghtLover · #5 11-23-2011, 07:41 PM

Quote:

Originally Posted by compress ignite

Is there any Lubricant "Recommended" for the Seat Tracks?

I'd almost suggest a Dry Lube Film,if nothing else is specified.
[Like is used on Sail Tracks and Zippers in Marine Use.]

CRC MARINE Lube at West Marine

I used small amounts of white lithium after cleaning them. Was a lot of work. I am betting there is a specific MB lubricant.

compress ignite · #6 11-23-2011, 07:42 PM

Mercedes HAS a Service Product for EVERY application.

LandYaghtLover · #7 01-05-2012, 09:34 PM

Bumping thread, sorta.

Its rather warm up here and I decided to attack this yet again. Took the control module out and found a few new traces that are toast. Not sure if its worth bypassing.

All the seat functions work except backward. If I fix the traces odds are reverse will work for a short bit until a trace burns up.

On the bench, the forward/backward driver motor works just fine still in the seat with power applied. When checking amp draw, it was the same in either motion.

The headrest issue I mentioned above is a mechanical issue, the motor is fine but something is binding. So I will ignore that for now.

Just want to seat to go backwards as it should without burning things up again.

Any thoughts, ideas? I checked in more detail and found all the wiring is in order and correct.

If all else fails I may just bypass the control module and wire it as if it was a non-memory version. But I would rather not.

Clemson88 · #8 01-05-2012, 11:06 PM

on this project. I'm just figuring out that the 86 model seats don't like the 84 model wiring.

If you could list your steps and post some glossy photos I would be much obliged. Circles and arrows with part names would help me understand where I am going. The following link is somewhat of an outline to follow but this being my first try I don't know the components of these seats so I don't understand exactly what is what.

complete seat transplant 90' 420sel to my 83' 300sd

LandYaghtLover · #9 01-05-2012, 11:18 PM

So your putting 86 seats in an 84. I might not be able to help. Mine are memory seats so I have a module in between the controls and motors on both sides.

Do you have memory seating controls?

LandYaghtLover · #10 01-05-2012, 11:24 PM

Here is a pic of he passenger side control harness. This comes from the door and plugs into the seat brain box.

Holmesuser01 · #11 01-06-2012, 12:49 PM

I pulled both of the seats and greased up everything that slides under there. The old grease in the little gearboxes is hard. It runs much quieter, now, and the motors actually spin a bit faster, and don't sound like they are laboring as much.

Used white lithium, too. I'm sure MB would frown on this.

LandYaghtLover · #12 01-06-2012, 06:01 PM

Well I got it back together. Lubed the tracks again. The repairs on the brain box seem to be holding up. I can operate the seat in all directions.

But I wired the head rest backwards, so for the switch up is down. Oops! And I need a new headrest motor. Mine "skips" a lot. I too it apart and found that the large gear inside must be damaged. Not sure how, but its the only thing that makes sense. I have to help it up and down. If the headrest it out, it operates fine but still skips. With the headrest it get stuck on each skip.

I dare not operate the seat in revers for more than a split second. Usually that burns up something. But now I can at least adjust the seat.

Memory seating is still a no go. I am going to dig deeper into it. I am not sure, but does memory seating only work in park, neutral, etc? My only though is that a wire is cut or its disabled by some means. Its too odd that both sides are dead though, so something is not right. Thats a project for another day I guess.