Thread: why do wheel bearings come loose?

I wonder why LR went to this later method when the old one seemed to work okay? On my old-style hubs I use the old method of measuring with a dial gauge - everything assembled and tightened, including the second locknut, check endfloat, (I think it's about .004" or so, but certainly almost nothing), and bend locktabs when you've got it. This is really no different to the method of "feeling" for hub play, I just find it easier. I did find that it was important to measure with the second locknut tightened up, otherwise you'd get some preload.

I always pre-load the bearings or within a month their loose,I also do mine with the wheel on and ''feel'' the tightness before finishing the job.It also pays to fold the tab washer over and pinch both nuts,I've seen them where the nuts can be moved because of the gap in the washer. Pat

I was under the impression all tapered roller bearings need some pre load.

I did check the hub for spin and wobble, but without the wheel. Id say there is nothing wrong with the LR procedure, but just me i.e. not enough experience.

PAT, not understanding your comment on the lock/tab washer, I bend it over the inner adjusting nut and the outwards over the outside lock nut.

I will say, that with the low torque setting of 10Nm(7lb/ft) for the adjusting nut setting, that there is room for error. The torque wrench, the thread of the stub and nut, how clean you have these etc. I found that doing it at 10Nm didn't remove wobble, but upping only 3Nm did. This checked only after the second, locking nut was installed to the correct torque setting.

Originally Posted by uninformed

I was under the impression all tapered roller bearings need some pre load.

I did check the hub for spin and wobble, but without the wheel. Id say there is nothing wrong with the LR procedure, but just me i.e. not enough experience.

PAT, not understanding your comment on the lock/tab washer, I bend it over the inner adjusting nut and the outwards over the outside lock nut.

I will say, that with the low torque setting of 10Nm(7lb/ft) for the adjusting nut setting, that there is room for error. The torque wrench, the thread of the stub and nut, how clean you have these etc. I found that doing it at 10Nm didn't remove wobble, but upping only 3Nm did. This checked only after the second, locking nut was installed to the correct torque setting.

That might be your problem. You may as well try it the old way so that you'll know by feel or measurement how much endfloat the bearings have.

Originally Posted by uninformed

I was under the impression all tapered roller bearings need some pre load.

I did check the hub for spin and wobble, but without the wheel. Id say there is nothing wrong with the LR procedure, but just me i.e. not enough experience.

PAT, not understanding your comment on the lock/tab washer, I bend it over the inner adjusting nut and the outwards over the outside lock nut.

I will say, that with the low torque setting of 10Nm(7lb/ft) for the adjusting nut setting, that there is room for error. The torque wrench, the thread of the stub and nut, how clean you have these etc. I found that doing it at 10Nm didn't remove wobble, but upping only 3Nm did. This checked only after the second, locking nut was installed to the correct torque setting.

"Pre load" doesn't mean tightening the bearing so it is under load.

It is a procedure prescribed for the conditions during installation, "pre" being loaded in service.

With taper roller bearings, unlike other rolling element bearings, the radial clearance changes dramatically with changes to the axial position of the cup and cone.

For example when determining preload for the taper roller bearings in an LT230 transfer case, you would consider the in service conditions where, for example the aluminium housing expands more than the gear assembly as temperature increases.

Originally Posted by uninformed

I was under the impression all tapered roller bearings need some pre load.

I did check the hub for spin and wobble, but without the wheel. Id say there is nothing wrong with the LR procedure, but just me i.e. not enough experience.

PAT, not understanding your comment on the lock/tab washer, I bend it over the inner adjusting nut and the outwards over the outside lock nut.

I will say, that with the low torque setting of 10Nm(7lb/ft) for the adjusting nut setting, that there is room for error. The torque wrench, the thread of the stub and nut, how clean you have these etc. I found that doing it at 10Nm didn't remove wobble, but upping only 3Nm did. This checked only after the second, locking nut was installed to the correct torque setting.

What I mean is when you fold the tab washer over make sure it's got a good pinch or grip on both nuts or the nuts will move,I set the inner nut so there is no wobble and free spinning,I then tighten the outer nut tight,I mean quite tight and check again,you will find the inner has tightened slightly also,if it's good I finish the job,if too loose or too tight back the inner in or out till it's right.I don't use a torque wrench,just feel. Pat

My method differs a little, first I ensure the bearings are properly packed and the races properly seated in the hubs. I fit the hubs and bearings and do up tight to seat bearings, then back off a Mickey Hair (MH), fit the wheel, spin and check for play(wobble), tighten adjusting nut till no play when pulling on top and bottom of wheel, back nut off half a MH, check for play again and if satisfactory, i.e. no noticeable play and rotating smoothly. Fit the lock washer and lock nut, run the locknut up till it holds the lock washer against the adjusting nut. Then bend the lock tab over the adjusting nut so as it doesn't turn when tightening lock nut.
Tighten lock nut till you can't move it (I call this F'n Tight), then I give the corner of the lock nut a couple of healthy whacks with a blunt chisel and a hammer, then bend over the lock washer, never had a problem with loose nuts, Regards Frank.

The following has nothing to do with why wheel bearings might become loose, but is for greater understanding of some things that are going on when wheel bearings are "pre-loaded", as per some of the posts above.

Firstly, although normally small, there is clearance between mating internal and external threads. No if's, but's, or maybe's, there is clearance. Because of manufacturing tolerance, the amount of clearance can vary from one installation to another.

Now take, for example, a right hand side hub assembly.

During the 1st stage of pre-loading the wheel bearings, when the inner nut is tightened against the outer wheel bearing and washer:

The right hand side flank of the internal thread (in the inner nut) is pushed against the left hand side flank of the external thread on the spindle/stub shaft. There will be some small clearance between the right flank of the external thread (spindle) and the left flank of the internal thread (inner nut).

Lets assume the tightening torque on the inner nut produced a bearing pre-load of say 10 Newtons (under the attraction of earth's gravity a 1 kg mass will create a force of 9.81N, or close enough to 10N for this discussion). I don't know, or care, how much tightening torque is required to produce a pre-load of 10N, it isn't important for this discussion.

To satisfy equilibrium (which the system must do), there will be a 10N force pushing to the left on the cone of the outer bearing (and washer) and this force will create a reaction force of 10N pushing to the right against the inner face of the inner nut (and washer). There must also be 10N force and reaction between the mating threads, right flank of inner nut and left flank of spindle.

During the 2nd stage of pre-loading the wheel bearings, when the outer nut is tightened against the inner nut and the tab washer between them:

The right hand side flank of the internal thread (in the outer nut) is pushed against the left hand side flank of the external thread on the spindle/stub shaft.

Now consider the case where the outer nut is tightened to produce 10N force against the tab washer and inner nut (approximately same tightening torque as applied to inner nut).

The pre-load on the bearings is unchanged, there will still be a 10N force on the cone of the outer bearing (and washer), and 10N reaction against the inner face of the inner nut (and washer). The force and reaction between the mating threads of the inner nut and spindle, now reduce to zero, and instead there is a 10N force to the left acting upon the outer face of the inner nut (and tab washer) and a 10N reaction to the right, acting upon the inner face of the outer nut (and tab washer). Now there will be 10N force and reaction between the mating threads, right flank of outer nut and left flank of spindle.

However if we continue to tighten the outer nut, beyond the 10N bearing pre-load, the inner nut (and the cone of the outer bearing, and washers) will be pushed further left until at some stage the left hand flank of the internal thread in the inner nut bears against the right hand flank of the external thread on the spindle. There will be clearance between the right hand flank of the thread inner nut and the left hand flank of the thread on the spindle.

Note: at this stage it should be clear that the thread of the inner nut is not contributing in any way to holding the hub assembly together. The inner nut is merely functioning as a spacer/washer, and only the thread of the outer nut carries any load from the wheel/tyre. Be alert, not alarmed

I can't predict what this new force would be, but it wouldn't need a strong arm, and could be determined relatively easily in a lab. Let us say for the sake of this discussion that it is 20N.

If we continue to tighten the outer nut further, the bearing pre-load will increase slightly due to small deformation of the mating threads in the inner nut, but now there is a force and reaction between the left flank of the thread in the inner nut and the mating thread on the spindle.

If tightened a lot more, the bearing pre-load hardly changes, but the forces and reactions increase between the mating threads of both nuts and spindle and between the mating faces of the tab washer and the inner and outer nuts. In other applications (not our wheel bearings) this is the objective with using lock nuts - create high forces between the mating threads so the friction prevents the nuts loosening. With our wheel bearings, the thin nuts the threads would strip if we tried to tighten them enough, so a tab washer provides mechanical prevention of loosening.

When we drive along the highway, pretending our Land Rovers are sports cars, the centripetal force on the tyres reacts through the hubs to the wheel bearings. The centripetal force can be much higher than the pre-load during assembly. At the limit of traction, this force will be higher on the outside tyre, but the load is carried by the inner wheel bearing acting upon the shoulder of the spindle/stub axle. However the centripetal force on the inside tyre is carried by the outer wheel bearing acting upon the outer nut (remember that in the direction of the load there is clearance between the thread in the inner nut and the mating thread on the spindle).

Off road, it is possible to get a situation where a much greater force is applied through the outer wheel bearing and retaining nut. Wedged against rocks, it could be possible to create a force exceeding the vehicle weight.

The only reason I can imagine for Land Rover providing the procedure that Serg stated, with the low torque values, is an attempt to get both retaining nuts to share the load from the tyres. However I have strong doubts that this is the case. My views on tightening procedure for the wheels bearings were stated in an earlier post.

The only time I have seen the threads of the spindle and retaining nuts damaged is when wheel bearings have collapsed, so no one should be concerned with the retaining nuts for their wheel bearings. I have only stated the above for enlightenment.