I was experiencing a slight shimmy whenever I braked hard at speeds in excess of 40mph. It felt like brake judder, but was intermittent, not at low speed. When I jacked up the car, I could move the front left wheel toe-in/toe-out about a quarter of an inch. An inspection from underneath while my wife moved the wheel showed that the ball joint into the left knuckle was worn and moving. Figuring that if the left one was bad, the right one probably would fail soon, I replaced both.
Last weekend, I replaced the front control arms on my 1997 528i. The parts are known by various names, but the parts are depicted in RealOEM as “5′ E39 528i Service kit control arm / Value Line”. Apparently, replacement parts are no longer available from BMW. RockAuto calls them “Control Arms” generally, and more specifically, “with ball joint; includes bushings; front left (or right) lower rearward”. They are Moog part numbers RK80529 and RK80530, but are not made by Moog (since they are not stamped with “Moog” on the parts). Some versions of the parts are available for $25 each. The ones with a Moog part number on the non-Moog box (possibly the same parts as the $25 units) cost $80 each.
Removal and replacement is generally straight-forward, with a few snags. Although it is only four nuts to be removed, the job took me almost two and half hours. I had jacked up the car the night before, removed both front wheels, and took a wire wheel on a Dremel to clean off the slight rust on the fasteners’ threads. Then I applied penetrating oil and let it soak overnight.
The wheels must be turned to extreme left or right to get the best access to the nut on the outboard end, which has a ball joint like that used on a tie-rod end. While I have a pretty complete toolbox, the nut on that ball joint was larger than my largest metric socket. I ended up using an SAE socket (3/4” or 13/16”, I forget), which worked well, perhaps because I had cleaned the threads the night before. (After you get your replacement part, you might want to check your sockets to see if you have one that fits the nut.) There is a thick (about 4 mm) washer under the washer with a tapered inner hole. That washer must be replaced in the correct orientation to work right (but you have a 50/50 chance if you don’t pay attention. The nut that was on the bolt holding the inner end to the frame came off easily using an 18mm box end wrench, with a 16mm box wrench on the bolt head.
Getting the ball joint (outer end of the control arm, at wheel carrier) was a different matter. It is tight, and there is little room to insert a pickle fork or to get a hammer on the exposed stud end of the ball joint. After a few failed attempts, I realized that I could insert the end of a long (about 10 inch) drift into the female hex in the end of the ball joint stud, and then hit the other end of the drift above the knuckle/carrier assembly. This made it much easier. A couple of hard hits with a hammer, and the outer end separated from the knuckle/carrier. I had to remove the bolt from the inboard end of the control arm to get enough clearance to get the entire control arm out. Since most of the structural components are aluminum, the bolt came out easily.
That is when I discovered that while I had removed the ball joint end from the knuckle, I was not totally done with the removal. I think that because the knuckle is aluminum, they inserted a large (about 1 -1/2” diameter) steel bushing between the male ball joint stud and the mounting hole in the knuckle. Getting the steel bushing off the ball joint stud was the most challenging part of the job.
I ended up holding the control arm in a large vice and driving a pickle fork between the ball joint housing and the metal bushing. It might have been that the space between the prongs of my pickle fork were too close, but I had to apply a lot of hammering to get that bushing off. On the second one (from the other side of the vehicle), it was even worse, and even applying a modest amount of heat was not successful. I ended up applying penetrating oil, and more heat a second time, plus a 40 minute wait, plus more penetrating oil, and then some more hammering to remove the bushing.
The second bushing exhibited a slight amount of corrosion, so I spent time cleaning it up with a brass wire wheel. I also used a small wire wheel in a Dremel to clean the bores of both bushings.
The first bushing slipped right back into place, and the control arm bolted up easily. Again, the washer on the ball joint has a tapered inner hole (which I also cleaned with a Dremel), so be sure you replace it in the proper orientation.
The second bushing was not as cooperative. It would not “slip in”. I eventually fabricated an installation tool from a length of ½” threaded rod, washers, and two nuts. Using the threaded rod like a bolt, I pulled the bushing back into the knuckle. Installing the control arm (first into the knuckle, then connecting the bushing to the subframe) was a simple issue.
It might not have been necessary, but I got the car aligned before I drove it any significant distance. I guess that, theoretically, the parts should have been the same, and the car’s alignment should not have been affected, but I was taught that any time one messes with the suspension, an alignment is warranted.
With 20/20 hindsight, I would recommend that you spray penetrating oil on the bushing/knuckle interface as well, and be liberal. Driving a large diameter bushing out of the knuckle takes a lot of force in the best of situations. If there is any serious rust on the bushing, it only gets harder.
For my car, this was not a simple “unbolt and replace” repair. In my opinion, any time one must start hitting parts with a hammer, the difficulty is increased. Also, it takes a bit of judgment to understand when one is hitting something too hard, and experience teaches a mechanic a bit of patience. A newbie might be prone to “using a bigger hammer” than appropriate, and damaging a part of the suspension. Pulling the bushing into the knuckle is not complicated, but in my opinion, is a more advanced process that might be a challenge for an inexperience handyman.
Thank you Brian from Ohio for this insight!