Posted on Feb 9, 2023 6:30 AM EST
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Recently, I reported on the gem of my toolbox: my beloved Hercules 20V 1/2 in. Compact 3-Speed Impact Wrench from Harbor Freight. And during its time in my care, it’s made wrenching on my 2011 BMW 128i noticeably more expedient due to its size and excellent breakaway and fastening torque.
However, with great power comes great responsibility, and sometimes the latter is as simple as ensuring nuts and bolts are threaded on straight. Oh yes, we’re going to dive into cross-threading fasteners, and here’s why this simple oversight took away several hours of my life that I’ll never get back.
And if you don’t believe it’ll happen to you, I’ll wait as it’s absolutely something that will occur in your lifetime. See this as an opportunity to commiserate in the comments and learn how to un-screw yourself. Literally.
Recently, I attended the 2023 season opener of SoCal’s Bimmer Challenge, a BMW-only time attack series that I had fun competing in during the second half of last year.
In preparation, I adjusted my car’s suspension setup to dial out a little body roll and understeer. To do so, I changed my Koni Sport shocks’ rebound by tightening the adjustment screw—or, adding rebound—ever so slightly to see what kind of a difference it’d make on track.
This is easy to do with the front dampers, as all you need to do is press the Koni key into the little nub at the top of the shock from inside the engine bay, and twist in the direction marked “FIRM.”
The rears, however, are a little more involved as you have to completely remove them, pull off their bump stops and mounts, compress them entirely, twist and feel for a slight detent, and then go about turning clockwise to stiffen. There are no clicks, you just have to keep track of the turns. There are also a total of five levels of rebound, with each level being a half-turn.
Despite having to fully remove the shocks, the only real pain is removing the trunk lining to get to the top bolts. Then, buzzing off the top and bottom nuts and pulling them out from the multi-link suspension. At some point in the past, though, I must’ve started the passenger rear’s bottom nut with my impact, as it would not spin off with either my ratchet or said impact. Well, that wasn’t smart.
Despite my best efforts to remove the nut while still mounted to the car, it was hopeless. Plus, because of its awkward position, I couldn’t simply grab my Dremel and go to town.
Luckily, this nut doesn’t thread through any suspension arm metal, just the rear lower rubber mount. Thus, I had to unbolt the rubber mount (no big deal), remove the lower control arm, get my massive prybar in there, and pop out the mount without damaging the very near brake line in the process. Doing all this took a minute, but eventually, it was out and everything around it was unscathed.
Up next, putting the assembly on my work table made life a lot easier, but I still had to cut the nut off, which, conveniently (not convenient at all), was of the stainless steel Grade 8 variety with a nylon locking portion. About an hour later, I finally cut deep enough with my barely adequate cutting wheels and was able to rip the rest of it off with a pair of pliers. It’s amazing how tough the little thing was.
Since the extraction had taken all of the shock’s threads with it, I then had to use a die set to create new ones. My only concern was whether there’d be enough meat left to cut into and still maintain structural integrity. Thankfully, this end of the shock doesn’t see nearly as much weight as the top. It’s fixed and only put under load during rebound.
I hopped in the freshly reliably running Audi S4 (more on that in a future blog), headed over to Loew’s, and bought an inexpensive SAE tap and die set. A nut and washer that’d match what the available metric sets could cut wasn’t in the cards, but that was a non-issue in my clean slate scenario. I went with a kit posssessing a size that translated to nearly the same as a metric nut that was one size smaller.
Cutting new threads is easy, it just takes a little patience. I secured the shock in my neighbor’s vise, and then sprayed the die with a little silicone lubricant that I had sitting around. Up next, I very slowly and carefully started spinning the die onto the rod with its accompanying tool. It took some physical effort, but I made sure to pause and confirm I was cutting reasonably straight threads and at not too much of an angle. With enough threading carved out, the new SAE nut and washer spun on without issue and I was good to go.
I’m normally good about threading on hardware by hand first, but I must’ve been in a rush or been a bit absent-minded when I last bolted the rear passenger shock into place.
It is annoying how BMW designed the rear shocks’ fitment, though. They sit in thick rubber mounts at an angle, so it’s a good idea to first thread in the bottom nut while the shock sits straight, then push it over to fasten the top from inside the trunk.
This teeny, seemingly insignificant misstep created a massive pain and, my God, is the lesson well-learned. But hey, that’s life. Messing up is a part of wrenching, and at least I’m thoroughly familiar with remedying similar issues in the future should they arise … as they probably will. Plus, this was the first time using a tap-and-die set, and I’m quite happy to have this in my toolbox for any future uses.
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Peter Nelson is a Staff Writer at The Drive. He often finds himself blogging about all-things motorsports and off-roading as he’s thoroughly infatuated with having fun behind the wheel. But his automotive enthusiasm is quite expansive and digs just about every corner of the industry.
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