Here is how I was able to fix my Herman Miller Aeron chair that had a broken tilt lock. Basically the pin broke off the sector gear.I know others have had the issue and might be looking for a cheap Aeron Tilt lock fix. I also found Herman Miller has a newer design on the tilt mechanism that removed this issue. Rather than pay 40 dollars for a new sector gear, I just did a quick hack to fix the broken post on the Sector gear myself.
First I want to mention that I am not a professional, and this post is for entertainment only. I am not responsible if try to do this and damage anything or injure yourself. I suggest having it professionally fixed. This post is just showing how I fixed my issue.
Aeron Disassembly
There are lots of videos online of the disassembly, but I will post a couple pictures for reference.
First remove the 2 6MM hex bolts holding on the seat on each side of the chair. Then remove seat.
Remove 2 Philips head screws from bottom cover.
Pry open the plastic cover to see the tilt mechanisms.
Once it was open I could see that the pin broke off the Sector gear. This was why I could not operate the Aeron Tilt lock.
Removing the Rear limit cam and the tilt sector gear was pretty easy. I removed a clip on the Rear limit cam and then after removing the spring from the Sector gear I could pull off both parts.
I did a little looking around at prices for a new Sector gear and found it ran about 40 dollars and came with the cable attached to it. Rather than spend 40bucks, I decided to try to fix it myself. I did this by basically drilling out a hole where the pin was previously located, then I Tapped it with a tap & die set. I had a 10-32 screw in the parts bin so ended up just using that as it was what I had on hand.
Here you can see the fix. Basically the part is just plastic so it was really easy to drill. When I put in the screw I used some Loctite to keep it in place.
When putting git back together you need to line up the arrows on the sector cam and the rear limit cam. Its a little hard to see here, but you can make it out on the Sector gear. I will try to get a better picture and update his later.
Then just put it all back together.
I did make a Youtube video of this and posted it online in case its helpful. Here is the link.
Summary of Aeron Tilt lock fix
That was it. I just put the chair back together and the screw seems to be holding the cable in place just fine. I realize the proper way for me to do this would have been to buy a new part. But I had the tools handy and decided to just try this out to see if it works. I will update this if it breaks or I have any more issues. I also did a video on it in case that helps out (link).