Details of ball joints
2008-08-07

      An important part of your car's suspension system is its ball joints. Made of extra tough steel, ball joints act as the pivot point between two parts: the suspension and your car's tires. This part help support your car's weight and, as is the case with some vehicles, they may be used to help set the alignment. Here are some details about Ball Joint:     

Definition: A flexible coupling in a vehicle's suspension that connects the control arm to the steering knuckle. A ball joint is so named because of its ball-and-socket construction. Some are designed to never require grease while others should be lubed every six months. As the joint wears, it becomes loose. The result is suspension noise and wheel misalignment     

Description: A ball joint consists of a hardened-steel, bearing stud and socket enclosed in a steel housing. The bearing stud is tapered and threaded and fits into a tapered hole in the steering knuckle. A protective boot prevents dirt from entering the joint assembly. Ball joints are used on the front end of virtually every car and light truck. Vehicles with conventional suspension systems use two ball joints per wheel: an upper and a lower ball joint. Cars with MacPherson strut suspension systems use a lower ball joint and an upper strut bearing rather than an upper ball joint.      

Purpose: Ball joints serve as the pivot points between the tires and suspension. Ball joints also support weight. On some vehicles, the ball joints may be used to make wheel alignment settings.     

Action£º There are two types of suspension systems that use ball joints. The first is a conventional system that uses an upper and lower joint. The second is called a MacPherson strut system that uses a single lower joint and an upper strut bearing. No upper joint is needed as the upper strut bearing does the job instead.     

 How do you know if you need to replace your ball joints?     There is a rubber boot that encloses the joint; inspect the boot for cracks or other damage. Another sign is clunking in the left or right front suspension; it starts off very subtle but will get worse as time goes on. I damaged my left ball joint when I hit a pot hole, it hit real hard! You can also check for free-play in the ball joint. Use a large pair of pipe wrench pliers (commonly called "channel lock pliers"). Put the upper jaw on the steering knuckle tab into which the ball stud is inserted. Put the lower jaw of the pliers on the underside of the control arm. Compress the pliers. If you see more than roughly a millimeter of play, the ball joint requires replacement. (Many manufacturers publish specifications for allowed play in ball joints. Unfortunately Porsche does not.) You cannot measure fatigue or damage to the ball joint stud. It would be possible to check it using a dye penetrant test, but this is beyond most shade tree mechanics' abilities. The only realistic approach to this problem is probably automatic replacement as some service interval, perhaps 100,000 miles for street-only cars, 50,000 miles for track cars.     

How to replace your ball joints?     Ball joints are the vital connectors between the steering linkage and axle assembly. Just as when baseball pitchers need rotator-cuff surgery, use and abuse can wear down ball joints, requiring replacement. Unfortunately for the do-it-yourselfer, many automotive manufacturers rivet the ball joints to the control arms in newer vehicles. As a result, removing original-equipment ball joints can require finesse and patience.

Step 1: Always buy name-brand steering components. These ball joints are from different manufacturers, but both are made in the good old USA.                            

Step 2: To diagnose a balljoint's health, perform the inspection tips listed above. If any problem is discovered, replace the joint.                                    

Step 3: Loosen the swaybar endlink (if applicable).                                   

Step 4: Remove the old joint's cotter pin and castellated nut.                                     

Step 5: Separate the balljoint using a prybar or pickle fork. Then loosely reinsert the stud in the knuckle.                                              

Step 6: Many shops use air chisels to remove balljoint rivets, but the do-it-yourselfer is better served with a drill. Service manuals normally give bit sizes appropriate for drilling out balljoint rivets without damaging the control arm.                                      

Step 7: Remove the balljoint, pulling down on the control arm for clearance if necessary.                                        

Step 8: Install the new balljoint — complete with grease fitting, rubber boot, castellated nut and cotter pin — using the hardware that came with it. Torque it to factory spec.                                         

Step 9: Lube the balljoint, wiping off any grease that spews out around the boot.