As requested by vwnate1 on my restoration thread, here is my write up of how to swap the cushions and upholsters from a W123 passenger seat to the driver seat, performed on my 1979 240D.

I picked up a seat in very good condition from a 1982 240D in the junkyard, the only caveat is that it was a passenger seat. I decided to go for it, since they only charge $50 for bucket seats.

First things first, I took apart the "new" seat. These are ridiculously easy to work with, compared to seats from a newer car. The only thing holding on the seat back was a small screw, remove it and use some force to push the entire back part down, then pop the whole panel out.



The panel reveals this button, which holds the headrest in. Push in on the button and pull up on the headrest to remove it.



Next, pop off all the plastic trim pieces. Word of caution, these are more fragile than our presidents ego, so be careful. They are held in with plastic tabs (including the adjuster knob) and I broke more than a few of them. Removing the plastics reveals the bolts holding the back of the seat the the bottom of the seat.



Remove the bolts and separate the two parts of the seat. Also remove the belt buckle - on my '79, the belt buckle is a different design than on the seat from an '82, and the seat seems to be a bit more "puffy".



After that, you can start removing the upholstery/cushioning. The only way that it is held in place on the seat back is these strips of leather sewn in around the edges. They simply push into the channel around the frame and hold the upholstery taut. To remove, have a helper stand on the seat to compress it and just pull the edge out from the channel. In the photo, the right side of the upholstery is still installed while the left side and bottom has already been removed.



Just remove the upholstery completely. Easy peasy.



The seat bottom is held together the same way. I opted to keep the seat bottom in one piece, as the springs are way better in the junkyard seat, but this photo demonstrates how the upholstery is held in place.



Next thing to get started on is the bottom. Remove the phillips head screws holding the rails in place. These rails will do you no good, since they are side-specific. There are 3 screws on each side.





You will be left with just the seat bottom, which is what you need anyway. The upholstery on the seat bottom does also have some small hog rings, but I did not take them off (since I am keeping the seat bottom intact).



Next, take your drivers seat out of the car and take everything apart the same way. I did have to remove the big spring, but it was not under very much tension. Popped it off with a screwdriver, same for putting it back. The seat rails install onto the passenger side seat bottom with no issues.



The armrest is held in with a 10mm bolt (already removed in this photo) and a large nut. I do not know what size the large nut is, but it was not very tight. I took it off with a pair of vice grips, and it barely took any force at all.



You can then take apart the original driver side seat back in the same way.



Then you can start reassembling the passenger side foam+upholstery onto the driver side seat back. Have a helper stand on the seat to compress everything, and just push the leather strips along the sides of the upholstery into the channel. Don't forget to tuck the springs into the horsehair/foam, they help keep everything in place.



Cut a hole for the armrest. I used scissors, but the same thing can be achieved with a razor blade, exacto knife, or screwdriver. If you are afraid of cutting the hole too big, mark it from the inside with a sharpie and take the upholstery back off so you can trim out an exact hole.



Then assemble the seat back onto the seat bottom and put the armrest back on. I didn't find (or even look for) a torque spec for the large nut holding the armrest in, so I just went for the classic German "gutentite" torque spec. Then you can install your headrest (I put my old style "cat ear" headrest on, even though the color doesn't match the new upholstery), put the back panel back on and put the screw back in.



Then put it back in your car and enjoy.



Some have mentioned that you can use pool noodles to stiffen up the seat slightly. I wrote this off at first, then I sat in the seat. The pool noodle seat stiffener is something I will definitely be doing when I get the car running again. Definitely a job that is rewarding and not as hard as I thought it would be.

The upholstery from your original seat can be swapped right over to the new foam, but my upholstery already had some rips, tears, and previous repairs, so I opted to put the lighter tan upholstery in. I will be reupholstering the entire car later on, so the mismatch is not a concern for me.

Hope this helps someone. I did this job by myself during my lunch break at work, but a helper to stand on the seat would have been nice.

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Milan Brown 1979 240D, rebuilt OM617.952 turbo diesel, rebuilt 722.315 transmission (my only daily driver)

Instagram: @maximed93

I tried the pool noodles on an SD and it was a waste of time because the noodles failed soon after. I remember a post where Mercedes still has available helper bumpers shaped like a column that fits into the round springs on the corner. They wern't much money and I don't have the PN or know that they are still available. Post if you find them.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

126-914-22-15-MBZ

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1981 240D 4sp manual. Ivory White.

Thanx Shern ! .

I have this issue but, my seats needs to have the cover removed, this means un doing the hog rings and swapping over the seat buns, much more involved and I'm askeert I'll ruin it all .

FWIW, the W126 spring supports are firm rubber cylinders that go in each front corner coil spring, different from the support pool noodles give .

Some have problems with pool noodles failing, most do not .

I'm a big FAT bastard (216#) so I know I'll be needing pool noodles in addition to the good used spring box .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

I have my old cushion that I need to pull apart to make upholstery templates anyway, I'll just document how that comes apart and goes back together for you this weekend.

__________________
Milan Brown 1979 240D, rebuilt OM617.952 turbo diesel, rebuilt 722.315 transmission (my only daily driver)

Instagram: @maximed93

THANK YOU good Sir ! .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Nice write up maximan.

Thank you Gasbeard. How did the transmission work out for you?

Upon further investigation, the foam is held on with hog rings - the upholstery is not. Just pop the edges out of the channel and you should be able take it off, same as the seat back. I will still update the thread with photos over the weekend.

__________________
Milan Brown 1979 240D, rebuilt OM617.952 turbo diesel, rebuilt 722.315 transmission (my only daily driver)

Instagram: @maximed93

I've put 2k miles on it and she gets me to work and back without fail. Major transplant success! Thanks for asking.