What does "worn out" mean for a spherical plain bearing?
It means the wear has gone too far for the job. A spherical plain bearing's service life ends when wear has increased the radial clearance or the temperature so that it can no longer work normally (Q1-04). So set a measurable end-of-life criterion, such as allowable radial play, noise or positioning error, in place of "run until failure". The right number depends on what the machine needs.
How do you check the play?
Unload the joint, clean it, then move it.
Unload and clean first. Play hidden by a load will not show, and grime can feel like slop that is not there, so wipe grease and dirt off before you test.
For radial play, hold the housing and try to move the ball sideways. You should feel smooth movement, not a click or a free movement before it catches. For axial play, push and pull along the bolt axis. A little smooth movement is normal, since axial clearance is usually larger than radial (Q1-07); look for a sudden step or a clunk. With the joint mounted, apply leverage with a pry bar radially and axially: visible movement or a clunk shows wear.
Then decide whether it is the bearing or the bore. With the bearing out, try to rock the outer ring in the bore. If it moves, the bore has lost its fit, not the bearing. Reddish-brown powder at the outer ring's contact with the housing points to the bore. Powder inside the bearing, on the ball or inner ring, points to the bearing. Both can be worn at once.
To put a number on it, measure the outer ring's outside diameter with a micrometer and the housing bore with a bore gauge. Compare the bore with the bore tolerance on the drawing (for example M7, K7 or H7, see Q1-06); a bore above its upper limit is worn. A light-load H7 fit is a clearance or near-zero fit by design, so a bore that equals or exceeds the outer ring's diameter does not by itself mean the bore is worn.
There is no single play limit for every joint. Check the maker's specification for the part. If none is available, a distinct click or measurable free movement is a reason to inspect or replace the joint. For scale, the clearance of a new bearing before fitting is listed by bore size and group in the maker's table (Q1-07). A fitted bearing has less, and a worn one more.
When should you replace it?
Replace the bearing, and look at the housing and pin too, when you see one of these. The causes behind them are in Q1-09:
- Play has grown past the limit you set.
- Rising turning torque, torque spikes, or a rough feel.
- Flakes or debris at the edge of the liner (maintenance-free types).
- Dents or flats on the ball.
- Corrosion or staining from water or chemicals.
- Reddish oxide at the seat of the bearing, which signals fretting. Check the fit and the bore before fitting a new bearing.
Replacing the bearing without fixing the cause repeats the failure. If a worn bore is the cause, a new bearing in it will wear out again (Q1-06). A bearing that was fitted with a heavy interference may not come out undamaged (Q1-10).
How do you check a suspension bearing on the vehicle?
With the same method, but the weight must be off the joint. Support the vehicle by the procedure in its manual so the suspension hangs and the pivot is unloaded, clean the joint, then pry radially and axially and move it by hand through its travel. Compare the movement with the limit that the vehicle designer or manufacturer gave; if none exists, a click or free movement is a reason to take the joint apart.
Look at the housing as well as the bearing. An aluminium arm can elongate its bore, and a welded cup can crack at the weld or loosen in the tube. Check the links and brackets around the joint after any heavy impact; a bent link can be the real cause of a worn bearing.
Because these are safety parts, regreasing does not cure play or damage that is already there, and a bearing with a dented or flaked ball is replaced, not reused. Play limits and inspection intervals for suspension and steering parts are set by the vehicle manufacturer or the organiser's current rules; nothing here is a rating or an approval.