Travis R

I got tired of my inoperable lumbar so I did some research and finally got around to repairing it. I really only cared about the lumbar, but I figured "since I was in there" I'd fix the side bolsters as well, especially considering all 3 parts with shipping came to ~$180 from www.mbpartscenter.com.
So let's just dive right in.

Step 1. Move your drivers seat all the way forward, tip the seatback farward, and raise the headrest. Take care not to smash it into the headliner, because it's got enough adjustment to do it.
Step 1b. Disconnect the primary battery in the trunk
Step B. Remove seatback cover using a T20 torx. Yours might be different because people lose random screws over the years.
At this point, assuming you are sitting in the back seat like I was, you should see something like this, minus the orange shoes...possibly



Step iii. I removed the 4 springs that hold the back support metal grid thingy (vertical yellow wires with bare metal horizontal wires). There is one each at the top left, top right, bottom left, and bottom right. They are quite strong so be prepared to muscle them a little to get them unhooked. Remove them completely from the metal seat chassis. They are in slotted holes, so it's not too tough once you figure that out.

Step IV. Snip all the zip ties that are holding things to the metal mesh.

Step 5. Separate the air line junction box. I used a small flat head screwdriver to separate the two halves. It has a little catch on each end. All the different colored air lines seal at this junction with a small o-ring. You need to be extremely careful with the air lines, mine were very brittle. Once the 2 halves are separated pop out the individual air lines from the inflator side.

Step NEXT. Gently move all the wires and hoses out of the way. You're going to have to wrestle the lumbar assembly (white felt rectangle) out from behind the mesh and you don't want to yank unnecessarily on any other connection. I decided to take mine out the left side because that's the way the hoses ran.
The white felt had 4 "tabbed" pieces that overlapped the metal mesh.

Once out, take a peek at the wonderfully aged plastic, that has been ravaged by heat and use over 15+ years. Mine looked like this:




They've wrapped the bladders in a perforated felt material to keep them from getting damaged against the seat during use.

If you only want to replace this one then just reverse all the steps and walk away happy. However, if you're a glutton for punishment like me, then let's continue with the side bolsters.

The side bolster inflators are mounted to a plastic "adapter". You can rip the bags and the felt off the mount if you want to be a caveman about it, but you won't be able to reassemble it that way. The plastic adapter has to come out.
These are held in with a T20 (maybe T25, can't remember) screw at the top and a tab that interlocks with the metal seat chassis at the bottom.
In this picture we see the top torx screw, and the plastic tab (not really visible) is just below the white sticker



Remove the screw and slide the top towards the back and up to disengage the tab at the bottom. This was challenging. I tried varying amount of back and up and eventually it came free. Remember the position that it came out, because that's roughly how the new one will go back in. It will also help to push forward on the brown/black straw-like material to make space.

For the outside bolster, Mercedes was kind enough to hide the torx screw BEHIND the side airbag... cool thanks. So you have to drill out the 2 rivets on the bottom. I used a ~.150" diameter drill bit and it worked great. If you use 1/8" drill bit it will be too small and you'll end up spinning the rivet. Ask me how I know.
Once the rivets are drilled out, being extra careful not to damage the little ground wire, pull the bottom of the airbag assembly out and down and it should become unclipped from the seat chassis.
There is a lot of extra wire for the airbag, so feed some of the extra through the seat chassis so you can flip it over and unplug it.
The orange tab has to be pulled (click) before the green connector and be removed from the airbag. Seen below in the fastened/secured position



Now that the airbag is out of the way, grab a small magnet and collect all the shavings from the rivet that fell into the seat and carpet.



Before you install the new side bolster bladder, make sure the felt is clipped onto the plastic adapter. This will help make sure it's in the right place after you've muscled it back into place. I have no idea how the attached zip tie was intended to be used, so I removed them. I always need zip ties for something.



The re-installation of the side bolster inflators was a real hassle. The tab on the bottom has to be engaged before you get the adapter into it's final resting place.
Here's all the things that have to be done simultaneously during this step
-You have to push the seat back mat (black/brown straw) out of the way, it's very stiff
-You have to get the tab on the bottom of the "adapter" lined up and inserted into the seat chassis
-You have to protect the delicate inflator and the felt material
-You have to make sure the curved portion of the plastic "adapter" doesn't get hung up on the seat chassis. It should go past the chassis and inside the fabric portion of the seat. This was the biggest struggle I had.

If you don't get the bolster inflator in the right position the tab won't engage, and the top screw hole won't line up.

Once you get the side bolster in place and screwed back down, install the new lumbar assembly. This will be a cakewalk by comparison.
Slide it in from the left side, it sits just below the fan assembly. Interlock the felt tabs with the seat support mesh.

I then reinstalled the 4 seat support springs we removed in Step iii, and reconnected (GENTLY) the air lines junction box. It'll only go back together (and clip) one way. And zip tie everything back into place.

To reinstall the side airbag, first plug in the green connector and push the orange tab to lock the it into place.
The slide the metal tabs at the top into their slot and feed the extra wiring back through the seat chassis.
I had to order some 5/32" stainless steel rivets. I only had aluminum and they weren't the right size anyway. Make sure you connect the little ground wire to the METAL mount, not the plastic one, on the bottom of the airbag.

At this point you can reconnect your battery and see how successful you were, and check for leaks.
Assuming it all works simply reinstall the seat back cover and attach it with the 2 screws at the bottom.

Knowing what I know now, I think doing just the lumbar would have been fine. The seat seems snug enough to me, side-to-side. But I might change my tune as a I play with the bolster inflators.

TLDR:
left side bolster "adapter": 211-910-01-75
right side bolster "adapter": 211-910-02-75
lumbar "adapter": 211-910-07-75
stainless steel 5/32" rivet from McMaster-Carr: 97525A458

bobgodd

Excellent write-up, thanks. I think it's good that you did the side bolsters also, because if I recall correctly, the system will stop operating if it detects a leak in any of the bladders.

tlambert

Cool write up. More like this is needed the older these cars get.

fazxs

Excellent! Very helpful.

kevm14

That is some dedication. Definitely qualifies as seat surgery. Glad to have this kind of writeup here but for me I think that confirms that I'll live with my leaky side bladders. Just because a bladder leaks doesn't automatically mean the system disables. It would only disable if it is unable to pressurize the bladder and the pump runs for too long. As long as the target pressure is low then it shouldn't have an issue and the other bladders will continue to work fine. That has been my experience now that I got a working pump.

bobgodd

Consider yourself lucky that your other bladders aren't leaking enough. My pump is working perfectly fine and still won't stay on due to leak, verified with xentry. It would be a shame to do this much work to leave some bladders leaky and have it not work as intended.

Travis R

Thanks. I plan to DIY pretty much everything on this car, and this forum is always my first stop.
My initial plan was to repair the bladders. I bought a couple different vinyl repair kits to see what worked best.
But once I got them out and saw how shredded they were, it was clear I needed complete replacements.
Used sets were going for roughly the same price as the new ones I found, so that was a no brainer.
I even thought about making my own from scratch and watched a bunch of YouTube videos about making your own inflatables. They would be pretty cheap to build, but the time would be something else.

kevm14

Wouldn't a used set be just as shredded anyway?

Dokus

Great to have a diy on this. Thank you.

Travis R

Potentially no. I​​​​​ saw some sellers on eBay offering a 90 day warranty. But for the amount of effort it would really be silly to put in used parts, IMO.

C32owner

Fantastic information, thanks for sharing your hard work ?😀

B@dnE55

My entire seat air system is not working, it gets power as I see red lights on the dynamic buttons, but no action. I seen a video where it could be a leak from the main air tube underneath the seat, but your operation just opened my eyes with these air bladder contraptions! Will have to check thos me out. Thanks for sharing.