Hello!

I just put in new seat adjust controls in my 87 300SDL / W126. For the most part, I was pleased to see my seats come back to life. However the one adjustmen I need most-- passenger seat slide-- is still dead!

Is there any way to manually adjust the seat slide position? Right now, I'd like to move the seat forwrds a considerable amount, but at some point in the future it'll have to move it back.

Thanks
rektide

If you have access to 12 volts, remove the wiring and hook 12 volts up to two wires, if no movement, move one wire to another pin. If no movement move wire to another pin. When you get movement if wrong direction switch wires.

On earlier W126's there is a box under the passenger seat that has a bunch of relays for the seat motors, not sure about the later versions. It could be that one of the relays is stuck, or connectors corroded.

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No! you can't manually operate the seat functions. A very likely cause of such a problem might be just the switch, and can be cured with a spray of contact cleaner! But if that doesn't fix it quick and dirty you'll need to dig deeper. You will need to determine if the functional problem is control malfunction or mechanical malfunction. The easiest way definatively determine that is to move the seat forwards and upwards as far as possible. From the rear you will be able to look underneath the seat bottom see the square black 4 pin connectors for the five individual electric motors. You can fabricate a pair of wire leads with female connectors on the ends and then one by one disconnect the individual connectors and plug the wire leads onto the large male pins. Then connect the other end of the wire leads to a 12 DC Volt source, that particular seat function will operate. Do this to each connector until you either find the one that operates the seat forward/back function or find all the other operating function and via the process of elimination determine the the forward/back function is actually mechanically inoperable. If you determine that the forward/back function does operate when connected directly to a power source you will likely need to start investigating, the switch operation first, then the wiring, then lastly the memory control unit under the seat.

If you determine that the forward/back function does not operate when connected directly you have an issue with either the electric motor operation or the mechanical gear drive of that function. This situation would likely require a removal of the seat and a closer examination to determine whether the motor or the mechanism is at fault and in need of repair or replacement.

If only this one function will not work and you can get by with only the occasional operation make up and connect a set of leads that you can use by connecting to a cigarette lighter pigtail. Plug the pigtail into the lighter, connect the leads and move the seat in the direction you need, reverse the pole connections to move it in the opposite direction. Coil up the leads and place them out of the way under the seat and keep the lighter pigtail in the glovebox. When you construct the pigtail make it so one wire is six inches longer than the other that way there will be less likelyhood of shorting the two together and blowing that fuse! Good luck!

X2 on the Contact Cleaner. It may work for 1 day or for years; spray a lot!!!

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daw_two
Germantown, TN

Links:
Sold last car --- 05/2012 1984 300D Light Ivory, Red interior
Cluster Needles Paint
New Old Stock (NOS) parts

Past:
3/2008 1986 300SDL "Coda"
04/2010 1965 190D(c) "Ben"
& many more

First off, thanks for the extremely well written reply.

That seemed likely given the flaky response I was getting, so I ebayed two seat adjust switches. I'm sure I could've irked out some kind of response out of one of them, if the motor/relay was properly behaving. The new switches have great "action" and appear to be in superb condition, but alas, no forward/back control.

Problem: right now the seat is as far back as possible! I can feel around and I think I know what you're talking about, but I doubt I'll be able to do anything with it.

I'm almost certain the forwards/back motor is burned out. It was quite a while ago, I was just sitting in my car, and I smelled that horrific smell of melting wiring. Underneath the passenger seat towards the front was quite hot. I think I managed to coax a tiny bit more movement out of it at a latter date, but that final act was the last it moved.

The passenger headrest may have a relay issue-- I can hear the motor enguaging for "down" but no response for "up", on both the old and new seat adjust switches.

I've started looking for a seat/track/motor mount, but its going to be another two weeks before I can get it installed, and the seat being so far back has really devastated my ability to carry the stuff around I need to carry. And further, now its preventing me from diagnosing what is wrong.

Are the seat/track/motor base units different for the driver/passenger side? Some of the parts I'm looking at list driver/passenger, others do not.

So, ah, any suggestions?

Problem: right now the seat is as far back as possible! I can feel around and I think I know what you're talking about, but I doubt I'll be able to do anything with it.

Actually this will only make the access to the area behind the seat more difficult, you should still be able to raise the rear of the seat and lower the seat front to get at the underneath of things.

If the electric motor has failed you’ve got a hard road because the rear two bolts will be hard to get at even with the seat rear elevated. The outside bolt can sometimes be accessed from the side using a swivel socket. The inside bolt is harder, you can sometimes get at it with a ¼” drive 10 mm socket on a T handle with it slid all the way to one side. The important thing is to just get the bolt to break free without stripping it then you can take and hour to move it 15 degrees at a time! A Gear Wrench is great if you can get it on the bolt head. Worse comes to worse you can grind the bolt head off using a die grinder and a good carbide burr.

Once you get the seat out you’ll need to get the seat base off the seat bottom which will require you in this case to figure out which electric motor drive the forward/back mechanism. Then you need to disconnect the drive cable at either the motor end or the mechanism end by removing the spring clip that secures the cable sheath. Once you get the cable disconnected you will need to take the actual drive cable and insert one end into the square cable receptacle at the mechanism and using something like a pair of small vice grips to grab the other end of the drive cable, rotate the cable and operate the mechanism to move the seat base forward or backwards to line up the access hole in the seat base to the large Philips head screw in the center of the seat bottom. The large Philips head screw is secured with blue loctite and usually requires some force to break free. I use a 3/8” ratchet with a 5/16” hex bit adapter and a large 5/16” Philips bit from a manual impact driver set you can get at AutoZone for $10. Of course you can also use any large regular Philips screw driver, you just want to avoid stripping the screw head down in that hole! With the center screw removed on both sides, work the mechanism forwards and then backwards to access and remove the other large Philips head screws at both ends of both sides. These six screws attach the motorized seat base to the seat bottom, unplug the wiring that goes to the two electric motors in the seat back, the recline function and the headrest function.

Now you can access the electric motors of the seat frame if you’re going to swap out a motor. Or it is probably easier to just swap out the entire seat base if you have one available.

Then place the seat base in position in the car, attach the four connections at the front and verify that the seat base operations all function properly. If everything works then you can attach the seat base to the seat bottom, remembering the seat back electrical connections and reinstall your tested working seat!

“The passenger headrest may have a relay issue-- I can hear the motor enguaging for "down" but no response for "up", on both the old and new seat adjust switches.”

With regard to the headrest function, if you can hear the electric motor operating when operating the switch the problem is most likely the plastic receptacle “key” part of the operator track which has failed. This issue will be most easily addressed with the seat out of the car, remove the seat back’s two small Philips head screws at its bottom and slide the seat back first down and then out. You can then easily see the headrest operator and its drive motor. This plastic part breaks and then functionality is lost, there are some quick fixes and replacement of the small plastic part will fix the problem permanently. If for some reason it’s not this usual problem it could be the drive cable from the electric operator to the mechanism, in the seat back all these parts are open to see and a problem will be apparent when you look at it.

Are the seat/track/motor base units different for the driver/passenger side? Some of the parts I'm looking at list driver/passenger, others do not.

The seat bases are basically the same, the electric motors are the same, the controls are not the same. The driver’s seat has the “master memory control unit” and the passenger side does not. You can use either seat base but would need to swap the controller onto any seat base that will be used for the driver’s side application. The one thing that I don’t know for certain is if the outside of the passenger seat base and the outside of the driver’s seat base are exactly the same, and I mean that only in respect to the openings in the seat base outsides that are there to accept the plastic prongs which attach the plastic trim to the seat base. I would be very surprised if they are not the same but I would check and get the plastic in place before I knew for certain. Good Luck!

Smelling the burning electrical component odor is NOT good. I think you are going to have to remove the seat (very difficult with the seat all the way back) and work on it out of the car.

I have a working seat adjustment frame with all 3 motors if you need one. I think they are the same from passenger to driver sides, but I would want to compare them to be sure. Does each side have its own memory?? Or is it just on the driver's side?

I also have 2 position memory seat adjustment switches.

__________________
daw_two
Germantown, TN

Links:
Sold last car --- 05/2012 1984 300D Light Ivory, Red interior
Cluster Needles Paint
New Old Stock (NOS) parts

Past:
3/2008 1986 300SDL "Coda"
04/2010 1965 190D(c) "Ben"
& many more

With the ignition on try opening the driver door and operating the seat controls.

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15 VW Passat TDI
00 E420
98 E300 DT
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97 S500
97 E300D
86 Holden Jackaroo Turbo D
86 300SDL
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I was able to move the seat on my 83 sd forwards manually. Not sure if its the same on an 87 126 but on the 83 there is a metal rod that goes from one side of the seat to the other. Its what is attached to the gears in the tracks on each side of the seat. I had to remove the bolts holding the seat down to get to it and lean the seat back. I used vice grips to turn the rod, which is grooved, and was able to get the seat to a more comfortable position. Check it out...

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VegStew
1983 300SD 70,000 WVO Powered miles
1990 300D In driveway with Head Off - Cracked

Thanks for the help all. With a small ratchet and a big breaker bar on the end of it, getting the seat out wasnt that much of a problem. Getting it back together, with the new working base, was easy-peasy. Thanks! May have some quick photos for reference posted in the future.