BMW’s original 8 Series is one of the most desirable classics for true enthusiasts, especially the V-12-powered cars. But the 850 CSi is the holy grail. It was essentially the first M8, as it had an M Division engine and performance features that no other BMW had at the time. Throw in its killer looks and it isn’t hard to understand why so many of us Bimmer nerds want one. However, there is one problem area: maintenance. More specifically, finding the parts to maintain them. And the most unreliable part of the 850 CSi was its “Aktive Hinterachskinematik” (AHK) rear-wheel steering system only available on Euro-market cars. Not only is that system prone to failure but there’s no aftermarket parts supplier that makes it or even makes replacement parts for it. So if it breaks, it’s nearly impossible to fix. Unless you’re a glutton for mechanical punishment like Sreten from M539 Restorations.
Sreten recently bought a Euro-spec 850 CSi, ironically from Virginia, equipped with AHK. And, of course, the AHK system wasn’t working. So being the madman that he is, Sreten set out to fix it. Miraculously, he did, but it wasn’t exactly easy.
The AHK unit itself is what’s impossible to source parts for. So if you want to fix it, you have to get creative. When Sreten removed it from the car and put it on the bench, he realized one of the solenoids wasn’t working properly, which caused the whole thing to stop working. So the adventure to take all of its solenoids out began and it wasn’t fun. A special tool was machined but only used on one of the solenoids. The rest took a ton of elbow grease, pliers, chisels, and likely many, many expletives.
M539 Restoration
Once the solenoids were out, he realized that they all worked just poorly, but the one problem child was in especially bad condition. Lack of used for a decade is likely the reason for their poor condition, as coatings were pealing and o-rings were failing. So he refurbished them with new o-rings and what do you know, they work. Once he put it all back together, he checked them again and it seemed like the whole system was working as it should. The true test was to fit it back onto the car and try it out.
After filling it up the car with power steering fluid, it was time to get nerdy. He plugged a laptop into the car to reset the system and have it run a test and… it worked. The AHK system finally worked and Sreten successfully rebuilt and fixed what is typically thought to be unfixable. Not only is it great to see such a rare feature on such a rare car fixed, but this should give any 850 CSi owners hope that it can be done.
