What is a ball joint and how does it fail?
What is a ball joint?
It’s is a ball-and-socket device that connects the suspension control arm to the steering knuckle. The ball-and-socket design allows the steering knuckle to rotate left and right and move up and down as it encounters road bumps. The joint is lubricated with chassis grease and the grease is held in place with a protective rubber boot.
The joint can be attached to the control arm by rivets or nuts and bolts, or pressed into the control arm and held in place with a retainer. Or, the ball joint can be an integral part of the control arm and not separately replaceable, in which case the entire control arm must be replaced when the ball joint wears or fails.
How many ball joints are there in a vehicle?
The number of ball joints used in a vehicle is based on the type of suspension used by the carmaker. For example, a front McPherson strut suspension includes a single ball joint located on the lower control arm. So the front suspension of a McPherson strut vehicle includes two ball joints. Don’t know what a strut is? See this post.
A conventional short/long arm (SLA) suspension, on the other hand, incorporates a ball joint in both the upper and lower control arms, totaling four ball joints.
Since the rear suspension only encounters up and down movement, most carmakers that employ an independent rear suspension secure the rear knuckle to rotating joint suspended in a rubber mount.
What makes a ball joint fail?
Since the joint moves with every turn of the steering wheel and with every bump in the road, the ball-and-socket interface can wear. Wear is accelerated if the rubber
boot is damaged because it allows the chassis grease to escape or mix with road water to form a sludge mixture that can no longer protect against wear and corrosion. In addition, a torn protective boot can allow road dirt into the ball-and-socket interface and grind away at the two components.
Is the ball joint grease able?
Most new cars are fitted with “greased for life” joints. The joint is filled with grease at the factory and the rubber boot is secured at the top and bottom with a spring retainer. Over time, the grease can degrade, causing metal to metal wear. Or, the boot can become damaged by contact with snow, ice or road objects.
Many aftermarket replacement ball joints include a grease able
“zerk” fitting which allows the technician to add replacement grease to the fitting. However, some untrained technicians fill the ball joint too much, causing the rubber boot to expand beyond its limit and burst. Once that happens, the ball joint is compromised and will experience rapid wear.
Symptoms of a worn ball joint
• Clunk or rattling noise when going over bumps. As the ball joint wears, excess clearance develops between the ball and socket. As the wheel moves up and down, the ball-and-socket clearance can produce a knock or clunk when hitting a road bump or speed bump.
• Creaking noise when turning. This is a sign of a completely dry ball joint, where there’s no lubrication between the ball and the socket. That metal to metal contact quickly wears out the joint.
• Vibration while driving. Since the ball joint serves as the anchor point for the steering knuckle, any excess clearance will result in movement as the vehicle travels down the road. This type of vibration can normally be felt in the steering wheel.
• Steering wander. Again, since the “anchor point” has excessive clearance it can’t maintain steering input. That causes the vehicle to follow road input rather than driver input. In that case, the vehicle can drift to the left or right on its own, even with driver correction.
• Uneven tire wear. In extreme cases, a worn ball joint can cause uneven tire wear.
How long do ball joints last?
Ball joint life is dependent on the suspension design, vehicle weight, vehicle alignment and driving conditions. Truck SLA suspensions, for example, tend to wear out ball joints must more often than a McPherson strut style suspension, sometimes in as little as 50,000 miles. The ball joints in McPherson suspensions tend to last around 100,000 or more miles.
What can happen if you don’t replace a worn ball joint?
As the wear increases the chances of the ball popping out of the socket increases. If the bottom or top portion of the steering knuckle detaches from the control arm, the entire wheel assembly can fold under the vehicle or tilt out from the top, causing catastrophic failure including death.
How much is ball joint replacement?
Replacement ball joints are available in many price ranges and quality levels. Ball joint prices for a 2010 Chevrolet Impala are offered by manufacturers like: Ultra-Power, Mevotech, Quick Steer, AC Delco, Mass and Moog. Retail shop prices for the ball joint part range from as little as $10 to around $70 for original equipment quality. The labor time to install two ball joints (left and right sides) on this 2010 Chevrolet Impala is around 1.6-hrs. plus an alignment. So the total ball joint replacement cost will be around $400 for parts, labor and alignment based on a labor rate of $100/hr.
What about cheaper ball joints?
There’s no industry policing for suspension part quality. Laboratory tests conducted by a major suspension parts manufacturer have proven that even though the cheaper parts claim to meet OEM specs, they don’t. Since the labor and alignment costs far exceed the parts price, it makes no sense to install an economy ball joint or any economy suspension part. In my experience, these parts wear out 30% to 50% faster than parts from a reputable supplier.
©, 2017 Rick Muscoplat