There are two parts of the lower control arm on E39 models like the BMW 525i that will wear out: the ball joint and the bushing. To test these parts, raise the front end of the car so that the tires are off the ground, grab the tire with your hands at the 9 o’clock and 3 o’clock position and shake the wheel side-to-side. There should not be any back-and-forth play in the wheel. In my case, the bushing had developed some play that was creating a knocking sound when driving over bumps. When we lifted the car and pulled on the wheels, the bushing looked like this: Also, check the rubber boots on the ball joints. If they get old, the rubber will tear and the joints will lose their lubrication.
- This project takes approximately 1.5 to 2 hours, depending on how easily the ball joints come loose and how long it takes to set the torque on the new control arms.
- Setting the torque on these control arms is a subject that has been discussed many times over on the forums. There are many schools of thought on this process, and this article is describing it as it is outlined in the technical manuals. This can be a trial and error process if you have never done this before. If you don’t feel like you are getting it right, don’t be ashamed to take the car to an alignment shop.
- Control arms should be replaced in pairs to avoid uneven handling or steering.
- Rust penetrant (WD40, PB Blaster, etc.)
- 16mm socket
- 22mm socket
- 17mm socket (or tire iron)
- Socket wrench (optional: pipe extension or break bar)
- 2 Jack stands
- Floor jack
- Adjustable wrench
- Pieces of 2x8 scrap wood
- Torque wrench that goes up to at least 90 foot-pounds
- Ball joint separator tool
Place car’s transmission in Park. Set the parking brake. Raise the front end by placing a floor jack under the central jacking point.
Install floor jacks under the rocker panel jack points. Use a tire iron (or 17mm socket) to remove the lug nuts and the front wheels. This is a grimy part of the car, spray all the control arm nuts with rust penetrant before starting. Give it a few minutes to soak. Use a 22mm socket to loosen the nut that secures the control arm to the front knuckle. You may need an extension on the socket wrench to break the bolt loose.
Set the ball joint removal tool to its tallest setting to ensure a good bite on the nut/bolt.
Run the nut to the top of the ball joint bolt so that the tool has more area to grab. The tool slides around the lower portion of the bolt and grabs the nut/bolt like this.
Turn the nut on the tool and let it develop pressure slowly on the ball joint bolt. Keep turning until the tool’s hold becomes tight. If it becomes very difficult to turn, walk away for a few minutes and let the pressure on the ball joint set in. It may pop loose during this time. If it does not pop after five minutes, continue tightening the tool. Maybe use a short extension on your socket wrench for more torque. Note, when the ball joint releases it will make a very loud pop, about the sound of a firecracker. It will startle everyone in the garage.
Remove the ball joint bolt, and be sure not to lose the washer. Remove the ball joint from the knuckle. Use a 16mm socket and an adjustable wrench to loosen the bolt on the bushing side of the control arm.
Now you can remove the old control arm.
If you get confused about which parts go on which side of the car, the control arms usually have a letter “L” or “R” cast on them to denote their orientation. Also, sometimes the new control arms are shipped with a protective covering for the ball joint boot. This is to be removed and discarded.
Install the new control arm, but keep the bolts finger tight just to get everything in place. You will set the torque in a few steps. Repeat this process for the control arm on the other side of the car.
Reinstall the wheels. Torque the wheel lug nuts to 89 foot-pounds. Lower the car onto two stacked pieces of 2x8 scrap wood under each of the four tires. This will keep the car level and give you enough room to still reach under the car and torque the bolts. Note that once the car is lowered onto its tires, the front suspension stands unusually tall, and the front tires may not be perpendicular to the ground. Bounce the front bumper of the car to release the tension in the front suspension. (Tip: If the suspension does not relax, it may be because there is too much friction between the tires, boards, and ground. This can be relieved by putting some lubrication, like dish soap, between the boards.)
Make sure that the steering wheel is properly centered. The car should be set to what BMW considers the proper loaded weight. In layman’s terms this works out to 150 pounds of weight in the driver’s seat, 150 pounds on the rear center seat, about 50 pounds in the trunk, and a full tank of gas. You can use sandbags or volunteers to sit in the car. In my case, my friend’s garage had lots of used parts laying around.
Check that the car’s height is correct by measuring the distance between the top of the wheel arch and the bottom edge of the wheel. Here are the recommended measurements for each available wheel size for 6-cylinder 5 Series cars with standard suspension E39 Bentley Manual has all the measurements for all variants of the e39 cars):
- 15-inch wheel = 22.8 inches
- 16-inch wheel = 23.3 inches
- 17-inch wheel = 23.9 inches
- 18-inch wheel = 24.4 inches
Use a 22mm socket to torque the ball joint nut to 59 foot-pounds, per the Bentley Manual
Torque the nut/bolt on the bushing side of the control arms to 81 foot-pounds.
Take the car for a test drive. If the steering pulls to one side or the other, loosen the nuts at the control arm bushings and repeat the process. It can be tricky to get this right. Don’t be ashamed to take it to an alignment shop if you can’t seem to get it right.
Eric Seeger is a writer and editor who has a taste for wagons. He has owned three Volkswagens, a Volvo, and is currently nursing two BMWs through life. All had a fifth door.