As most of my readers know, I have a very nice Aeron chair that I got when I was working at home full time. The decision to invest $600 in a single piece of furniture I was going to use day in and day out wasn’t lightly taken, but I needed something comfortable, durable, and designed for my size and weight. An Aeron size C from ebay fit the bill nicely.
I’ve had my share of problems with it, including a broken ‘pan’ seat and a damaged lifter. The seat was covered under warranty, and I was able to replace it myself, but the lifter needed a trip to a local repair shop.
The last couple weeks, the chair has refused to recline. The levers on the left side that allow forward and backward motion were ‘locked’ in position, and I couldn’t undo them. It was making me not want to sit at my desk – and even though I’m not working fulltime at home, I know that if there’s something that makes an experience less than enjoyable, I’ll avoid it. So I was sitting on the couch with my laptop or working downstairs.
Last night, I decided to haul out the toolbox and see what could be done…
First and foremost, I don’t recommend anyone who isn’t comfortable crawling around on the floor, and possessing a decent set of tools to attempt these sorts of repairs. The Aeron chair is built with an eye toward long term maintenance and durability. It has Real Live Parts in it, so you should use Real Live Tools to work on it.
Since the problem I was having was with the recline mechanism, I traced the cables from the levers. They disappear into that formless box underneath the seat. After some wriggling around, I decided I needed to remove the seat to get better access to it.
Much of the chair is held together with allen-head bolts, so having a good set of standard-sized allen wrenches is required. Remove the two bolts from the sides of the pan, and remove the two bolts at the end of the arms under the mechanism box. They came out easily for me, but they were obviously snugged in. Once those bolts are out, pull the seat out and set it aside.
The next step is getting the box open. It’s a plastic housing that has only 2 screws visible on the outside – a set of phillips head screws on the bottom. Don’t undo those yet. The plastic housing is one of those ‘snapped together’ arrangements. I had the benefit of having the housing loose already, so a little prying and wriggling with a large flathead screwdriver, and the whole assembly popped apart. This is fairly rigid plastic, so don’t twist, you could break off the tabs, but gentle pressure around the joining edges will win out, and the top will pop off.
Once the top is off, you can see the mechanism inside. For the problem I was working on, I needed to reach the underside, so I undid the two phillips head screws, and pulled the bottom cover off. These screws, by the way, are sheet metal screws, not mechanical screws. They thread into the metal of the chair. Don’t lose them!
The chair mechanism is remarkably simple, and made sense once I looked at it. It was obvious that the two levers control the distance the chair can tilt one way or the other, using a set-bolt on one side, and a rotating cam on the other. The rotating cam designates how far back the chair will tilt, the bolt sets where the forward tilt stops. While wiggling the cables around, I realized that the tilt mechanism had gotten jammed with the forward tilt saying “FURTHER BACK” and the back tilt saying “FURTHER FORWARD”. The only way to unjam these was to take pressure off one side of the mechanism so they could rotate. But how to do that?
The answer came in the set bolt under the forward tilt. There’s a massive assembly there (for a chair) obviously taking all the pressure for the forward tilt. It has a large (allen-headed) set bolt, accessible from the bottom, that can be used to adjust the ‘stop point’. I set my largest wrench into that bolt, and backed off the tension 1, 2, and… POP! Something moved. Looking to the other side of the tilt mechanism, I had relieved enough tension that the recliner cam had snapped back to where it was supposed to be. Now the levers were operating properly! I could slide the recline lever up and down and see the cam rotate from one side to the other. Score!
| Position 1, upright | Position 2, allow recline |
|---|---|
 |
 |
| Note the position of the cam – when it’s spun ‘out of the way’, the chair can recline. | |
After puttering around inside for a little, getting an idea how the tensioner for the recline mechanism works (it’s a lateral screw driving a spring – maybe I’ve worn out my spring, because running the tension from stop to stop via the knob on the side never really did anything), I decided it was time to pack up. Reassembling was relatively easy, except for getting the panel screws back in place. Remember, not mechanical screws, and in an awkward location. The answer came when i figured out you could see through the mechanism to where the screw was attempting to thread into the mount. A bright light down there and I was able to line up the screw properly.
Reassembly was easy – two screws to put back on the lower housing – be careful to lay the control cables back into their slots, or else the housing won’t go together correctly. 4 bolts to put the seat pan back in place, and I was done.
I am very impressed with the construction of the chair. It has solid, well designed parts all the way through it. This sort of repair / issue with a cheaper office chair would have meant me throwing it out and likely replacing it with a new one, but Herman Miller did well with these things, and repairs are quite possible and worthwhile. My chair is back to being it’s normal comfy self.
If you bought your Aeron Chair off ebay, how were you able to get the seat replaced under warranty if you aren’t the original purchaser?
The vendor selling on ebay warrantied the sale.
Hey Eidolon,
have just repaired the hight adjuster on my Herman Miller Mira chair by following your post. Thanks!
Hello!
I need to repair the up down slide on my chair. Right now the chair slides to the bottom position and I cannot get it to stay up.
I am hoping your comment means that it is possible to fix the height adjuster by opening the black box.
thanks
I don’t think you’ll find a fix for that in my article. You’re talking about the gas cylinder failing. You’ll need a replacement, like one of these: https://www.amazon.com/Gas-Cylinder-Replacement-Aeron-Chair/dp/B009WBS0LE
@russ Awesome! Glad I could help.
Thank you very much for this post. I had the same issue and just repaired it instead of sitting here grumpy.
Hi!
I found your post to be very helpful and informative. I am currently trying to upgrade my basic aeron to a highly adjustable one by adding on the tilt limiter and forward tilt knobs. Based on your knowledge, would it be difficult to add in those components into the base? If so, could you give me a few pointers on how I would be able to do that? Thanks
How do you fix the height adjuster on the Herman miller chair??
This is about 9 years late for you, but will maybe help someone else. I replaced a bad hydraulic cylinder for my aeron chair (non oem bought off amazon) and put chair back together and chair would go up but height adjust didn’t work. The cable was working inside, pulling down on the little lever above the cylinder top, but nothing was working. I found online that if you remove the height adjustment piece (2 screws) above where the hydraulic cylinder terminates, you can see if the set screw right over the top of the cylinder top is flush with the plastic arm bottom or not. Either way, re-set it so that it is flush with the bottom of the movable little arm. Put the assembly back over the cylinder top and tighten with the 2 original screws. Now, using an Allen wrench and leaning a bit of your weight ( a knee works) on the chair, start slowly turning the set screw clockwise. After a revolution or two the chair will all of a sudden sink down. Now, back the set screw counter-clockwise 1.25 turns back. I found this fixed my height adjustment problem, with a new cylinder of course. Took me a while to find how to do this, so hope it helps someone out there like this article has helped most of us!
I’m having trouble opening the plastic housing on the box under the seat. The very rear-left part of it comes very loose (I can even fit the rounded, thicker part of my flathead screwdriver between the two edges), and there are two tabs I can see there, but I can’t find tabs anywhere else in the joining edges. In all other areas of the housing it barely budges. Any further specifics you can give on tab placement or method for opening the plastic housing? Any relation between opening the box and the two rotating pieces at the very front sides of the box, where the backrest connects to the box? The pieces I’m referring to can be clearly seen in these photos:
http://www.flickr.com/photos/planet-geek/3087265718/
http://www.flickr.com/photos/planet-geek/3087265878/
It’s the piece between the box itself and the apparatus that houses the backrest and the chair controls.
This was an almost spot-on do-it-yourself guide.
The only variations I encountered were:
1) The stop screw in my chair was frozen with rust and the head threatened to strip with a #6 (metric) allen wrench. I found an alternative way to free up the chair…
2) After taking out the seat and removing the control cables out of their respective slotted housings, I was able to apply pressure to the back of the chair slowly, forward and back, until I was able to see which of the two cables was the bigger problem (in my case, it was the recliner. Once that gave and the recline stop relaxed, I was able to return the chair to normal operation.
It’s amazing how well built this thing is. (I’ve had mine since 1999 and this is the first problem I’ve had with it with daily use almost the entire 10 years.)
Thanks again for the walkthrough.
Great walkthrough!
I have a slightly different problem with my new Aeron. The thing is that I prefer to sit straight up when working. When I use the STOP tilt to lock backward tilt, it still moves back a bit and does not stay in the straight position it is in normally. Can you tell me which screw I need to adjust this?
Thanks in advance for your help!
I had the same issue, but after taking my chair apart (I have a pre-2004 chair) and speaking to Herman Miller, I saw that my ‘white bumper’ was worn down. My white bumper differs from the one pictured in David’s pictures, but it serves the same purpose, to keep the rear limit cam into position.
I also tightened the tension screw on the inside of the left arm that holds the front and rear tilt limiter cables. Models vary, so searching for schematics online before working on your chair is advisable. I hope that this helped.
I have same problem but can’t find th part for sale anywhere, does it have a part number or anything? Thanks.
Martin, I managed to find the part on this page: http://www.thebackstore.com/backstore/Herman%20Miller%20Sale/HermanMiller/Aeron-Parts.htm
It is part 55, and it cost me $24 shipped.
I just ordered it so I cant say if it is the right part or not.
I found it for $10 here: http://www.aeronsale.com/store/p34/Rear_Tilt_Plastic_Stop_.html
Great post………thank you! I had the same problem with the tilt movement. it was stuck/jammed and I managed to overcome it with your helpful post!!
hi thanks for great help can you get proper clear photos or video please
The photos are as clear as I can make them. The post you’re commenting on is almost 10 years old 🙂
I need to replace the seat cushion on my chair – anyone have any idea how this is done?
When I broke my seat pan on that chair, I just ordered a replacement from Herman Miller. You can also probably find the on ebay. That’s the general term for them, btw ‘seat pan’. Make sure you get the size that’s appropriate to your chair (A, B, C, etc).
I bought a new seat on eBay for a chair I purchased at an estate sale. It’s incredibly easy to change it out; see the article posted on ” Apartment Therapy” for full directions & list of tools & sizes of metric hex screws.
Great piece. Fixed my chair just fine.
I have adjustable height arms on an aeron chair. The adjustable know broke. How do you replair it?
Should read “adjustable knob”
I was recommended this web site by way of my cousin. I am now not sure whether this publish
is written through him as nobody else know such designated
approximately my problem. You’re wonderful!
Thank you!
The tilt tension adjustment on my Aeron does not work. When I turn the handle, the axle does not follow it. Any ideas how it can be fixed?
Thanks for the walk-through. Upon fixing the exact issue as above. I realize my chair won’t tilt along my back (won’t stay up). The chair became a locked chair and won’t come up (stays at the tilt limit position). Do any of you have this issue, do I require to replace my whole tilt mechanism or some resetting is needed, thanks. Any ideas how it can be fixed?
Hi Dave, I know this is a very old thread, but just wondering if you ever ended up fixing your tension knob/rod.
Did you ever get that to work again? Right now I have a similar issue I cannot add resistance to the tilt. All. Lever and locks work great though
I didn’t, sorry! Just never chased it down. Good luck!
Fantastic post! My “adjustable” arms are frozen in place and no matter how much or what direction I turn the dials on the side (anyone know which model this is? I don’t have a label) I cannot get the arm rests unlocked so I can adjust them. Maybe the bolt is simply stripped. Will I need a new Arm Bolt Assembly?
Also, I have the opposite problem on the chair tilt. I lock it upright, but sometimes without hardly any pressure, whatever is holding it in place (the white bumper referenced above?) gives out and the chair suddenly tilts back and my back is now sore from my instinctive recover (maybe I should actually just stop sitting in it). Could it something other than the white bumper? When I push the lever all the way down, I can adjust the tilt and lock it into any position…it just won’t stay there.
Any thoughts on these issues greatly appreciated.
Just want to say I have this same problem (Cindy) and am seeking the answer. My backward tilt will “lock” but sometimes with no pressure at all it will slip and fall backward quickly! For a while I zip tied it in place but now I am resolved to fix it…someone help us figure this out?!
thanks for this post: timeless design = timeless manual
just helped me fix my forward tilt 🙂
Hello folks. My chair is locked at a down position without being able to bring it up again. Any idea ?
the post on our chair “broke” thru the base leg housing. We have bits of a plastic piece, washers and ball bearing fixture that were in the base. do you have any experience with this type of breakage?
Thanks.
Hi, any ideas? My aeron chair seat dropped below me, I needed to replace Classic Hip Pivot Bolt (MK2), I purchased but removing the old one has become a nightmare. The allen threads are damaged so I had to use a screw/bolt removal part, but there is not enough torque on my drill to remove the bolt. I bought a monkey wrench and Waterpump Pliers , but neither would remove the bolt, I used a blow torch to get through the plastic to the metal casing screw as the wrench merely twisted the outer casing. now I am down to the inner metal bolt but there is no leverage to turn the bolt.
After 4 days I am ready to put in the trash unless someone can advise! 🙁
Many Thanks! Twelve years later, your instructions helped me repair an Aeron that I bought for 150$ because of this specific trouble.
This article worked like a charm!!! THANK YOU DAVE!!!
Almost 14 years later and this tutorial solved my issue when all the others failed. Thank you so much! I never would’ve figured out the set bolt under the forward tilt.
Your guide was great! Glad I found it!
Unfortunately, for me the cable broke on the front tilt. However, using your guide, I was able to remove the spring and override the forward tilt limiter.
Thank you again.
You’re very welcome! I’m glad it was helpful!
14 years later, and you’ve helped yet another person. I can lean all the way back now! Holy crap!! THANK YOU!
You’re very welcome! Glad it was helpful!
Hi Dave, what you describe is what seems to be wrong with my chair as well although it looks locked very strongly, that shaking doesn’t appear to loosen it.
Can you see this pic? Any advice is much appreciated
https://imgur.com/a/FS49INm
Hi Dave, this is what the cam position for the tilt limiter looks like
https://imgur.com/a/FS49INm
I turned the Allen bolt under the forward tilt limiter side untill it isn’t even touching the chair anymore and no luck. Any thoughts? Thanks in advance