What an upper control arm does and why it fails

Your upper control arm is a metal rod that connects your wheel hub to the frame and lets your wheel move up and down while you drive. Over time, the ball joint at the end wears out from friction and road impacts, causing a clunking sound when you turn or hit a bump. Once it starts to fail, the arm cannot hold your wheel in the right position, which makes steering feel loose and can damage your tire.

Replacing the upper control arm means removing the old one and bolting a new one in its place. The job takes two to four hours if you have basic tools and a safe way to lift the car. You will need a jack, jack stands, a socket set, a ball joint separator tool, and new bolts if the old ones are damaged. Many shops charge $300 to $600 in labor alone, so doing it yourself saves money if you are comfortable working under a raised vehicle.

Key Takeaways

  • The upper control arm connects your wheel to the frame and fails when the ball joint wears out, causing clunking and loose steering.
  • You will need a jack, jack stands, a ball joint separator, and a socket set to remove and install the new arm safely.
  • Always support the car on jack stands before working underneath it, never on a jack alone.
  • The ball joint may be pressed into the arm or bolted on; check your vehicle's manual to know which tool you need.
  • After installation, have the wheel alignment checked because the new arm changes your suspension geometry.

Gather your tools and parts before you start

Buy a replacement upper control arm from an auto parts store or online retailer. OEM (original equipment manufacturer) parts fit exactly but cost more; aftermarket arms work well and cost less. Bring your vehicle's year, make, and model to the parts counter so you get the right arm for your side—left and right are different.

Collect your tools in one place: a floor jack, two jack stands rated for your car's weight, a socket set with metric or standard sockets (depending on your vehicle), a wrench set, a ball joint separator tool (a two-jaw puller that costs $15 to $30), a hammer, and new bolts if the old ones strip during removal. Wear safety glasses and work gloves. Park on a flat, level surface away from traffic, and set the parking brake.

Lift the car safely and remove the wheel

Loosen the lug nuts on the wheel by a quarter turn while the car is still on the ground—this makes them easier to remove once the wheel is in the air. Position the floor jack under the frame near the wheel you are working on, not under the plastic trim. Raise the car until the wheel is six inches off the ground.

Slide a jack stand under the frame on each side of the car, then lower the car onto the stands. Never work under a car supported only by a jack. Remove the lug nuts completely and set them in a cup so you do not lose them. Pull the wheel straight toward you and set it aside.

Disconnect the ball joint from the steering knuckle

The upper control arm connects to the steering knuckle (the part that holds your wheel) through a ball joint. You will see a castle nut (a thick nut with slots) holding the ball joint stud in place. Use a wrench to hold the nut while you loosen it with another wrench, or use a socket and ratchet. Do not remove it completely yet—loosen it until it is hand-tight.

Tap the steering knuckle with a hammer near the ball joint stud to break the joint loose. Once it moves, unscrew the castle nut the rest of the way and remove it. Slide the ball joint separator tool over the stud and tighten the tool's center bolt. The tool will push the stud out of the knuckle. Remove the tool and pull the knuckle away from the arm.

Remove the bolts holding the arm to the frame

The upper control arm bolts to the frame at two points near the top of the wheel well. Look for two bolts running through rubber bushings. Use your socket set to remove both bolts—they are usually 15mm or 18mm. Keep the bolts in a safe place; you may reuse them if they are not stripped or bent.

Once both frame bolts are out, the arm is free. Pull it away from the car and set it down. If the arm is stuck, tap it gently with a hammer to break it loose. Do not force it or you may damage the frame.

Install the new upper control arm

Position the new arm so the ball joint stud points toward the steering knuckle and the bushing holes line up with the frame holes. Insert the two frame bolts by hand first to make sure they thread correctly. Tighten them with your socket set in a crisscross pattern—tighten one bolt a few turns, then the other, then back to the first. This keeps the bushings from twisting. Tighten until snug but do not over-tighten, which can crack the rubber bushings.

Slide the steering knuckle back onto the ball joint stud. Thread the castle nut on by hand, then use your wrench to tighten it. Tighten until the nut is snug, then check that one of the castle nut's slots lines up with the hole in the stud. If it does not, tighten the nut a bit more until a slot aligns. Insert a cotter pin through the hole and bend the ends to lock it in place. If your vehicle uses a different locking method, follow your manual's instructions.

Reinstall the wheel and lower the car

Slide the wheel back onto the hub and thread the lug nuts by hand. Lower the car slowly onto the wheel by raising the jack stands and then lowering the floor jack. Once the wheel touches the ground, tighten the lug nuts in a star pattern—tighten one, skip one, tighten the next, and so on. This keeps the wheel centered. Tighten them firmly but do not use all your strength; over-tightening can strip the studs.

Remove the jack and stands. Drive the car slowly to a wheel alignment shop within the next few days. The new control arm changes the angle of your wheel, which throws off the alignment and causes uneven tire wear and pulling to one side. Alignment is not expensive and takes about an hour.

Common mistakes to avoid

Do not work under the car on a jack alone—always use jack stands. A jack can fail and the car can fall on you. Do not reuse old bolts if they are bent, stripped, or corroded; new bolts cost a few dollars and prevent the arm from coming loose. Do not skip the wheel alignment; driving on a misaligned wheel wears the tire in weeks and makes the car unsafe to steer.

Do not force the ball joint separator tool or hammer the steering knuckle too hard, which can crack it. If the joint will not separate after a few taps, spray penetrating oil around the stud and wait 15 minutes before trying again. Do not tighten the frame bolts too much; the rubber bushings need to flex slightly, and over-tightening hardens them and causes noise.

Frequently Asked Questions

Can I replace just the ball joint instead of the whole arm?

Some upper control arms have a ball joint that is bolted on and can be replaced separately, but many have the joint pressed in and require special equipment to remove. Check your vehicle's manual or ask a parts store whether your arm has a replaceable joint. If it does, you can save money by replacing only the joint.

What if the bolts are stuck and will not come out?

Spray penetrating oil like WD-40 or PB Blaster around the bolt heads and let it soak for 30 minutes to an hour. Tap the bolt with a hammer to help the oil work in. Try loosening again with your wrench or socket. If it still will not budge, explore heat with a heat gun for a few minutes to expand the metal, then try again. As a last resort, drill out the bolt, but be careful not to damage the threaded hole in the frame.

Do I need to replace both upper control arms at the same time?

If only one side is worn, you can replace just that one. However, if the car has high mileage, the other side is likely to fail soon. Many mechanics recommend replacing both at once to keep the suspension balanced and avoid a second job in a few months.

How do I know if my upper control arm is actually bad?

A worn upper control arm causes a clunking sound when you turn the wheel or hit a bump, loose or wandering steering, uneven tire wear on the inside edge, and sometimes a vibration in the steering wheel. A mechanic can confirm it by lifting the car and grabbing the wheel to check for play in the ball joint. If the wheel moves up and down more than a quarter inch when you push and pull on it, the joint is worn.

Will I need new bolts when I install the new arm?

Reuse the old bolts if they came out clean and are not bent or stripped. If they are corroded, bent, or the threads are damaged, buy new ones from the parts store. Bring the old bolt to match the size and thread pitch. New bolts cost just a few dollars and are worth the peace of mind.