Wheel Bearing Preload - How to check Hub Temp? (1 Viewer)

[agaisin]

on the topic of how wheels separate:
http://www.crashforensics.com/wheelandhubfailures.cfm
The last section deals with hub failures and their explanation for why overtightening adjusting nuts can cause failure is that it forces out the lubricant from between the bearing rollers and races and causes overheating and fatigue which in turn can lead to a full bearing lockup and hub separation.

the timken tapered bearing damage analysis and other sources had led me to believe that overtightening can also cause deformation of the bearing - but i guess that it would require waaay more than 53 ft lbs to deform the bearing components so the more likely form of failure from overtightening is tied to lack of librication by effectively squeezing it out from between the moving parts.

the reason i bring up root cause of failure by overtightening is that if you forced out the lubricant by overtightening i think you'd know by the high heat. If you deformed the bearing by overtightening (doubtful) i don't know whether you'd be looking for heat or the more likely symptom is you'd expect to hear/feel something. i imagine that (slightly) deformed parts would also translate into more heat, but even bf that you'd know by sound/feel that something's wrong?...

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[TrekboxX]

Good article, but it puts as much emphasis on the danger of under tightening as over tightening. As far as using the high torque value I came to being a sign of worn/damaged parts- I see just the opposite. The bearings and races were brand new Timken, but even if they weren't, a damaged bearing should be harder to turn than a "perfect" one, and thus require less nut torque to get the same preload. Either way, this is all academic. I am convinced about the preload not being too tight. I'm just afraid to tear it all back down again without distinct direction. I guess the first step is temp checks, then go from there. You're right, if it's not clanging about or overheating, it shouldn't really matter what the spring scale says...

 

[SupraTuRD]

Yikes!!!

Sounds like most of you are over-torquing your bearings by at least 4X!

The FSM specification of 9.5-15.0 lbf... as in pounds per foot. The specified preload value should be measured at 12" to attain the specified values. Since the bolt circle on our rigs is 150mm with a radius of 75mm/2.95" (call it 3"), the specified FSM values must be divided by 4.

Therefore, at the fish-scale attached to the lug, the target value is 2.375-3.75 lbs.

Toyota needs to make this more clear in the FSM.

 

[agaisin]

Sounds like most of you are over-torquing your bearings by at least 4X!

The FSM specification of 9.5-15.0 lbf... as in pounds per foot. The specified preload value should be measured at 12" to attain the specified values. Since the bolt circle on our rigs is 150mm with a radius of 75mm/2.95" (call it 3"), the specified FSM values must be divided by 4.

Therefore, at the fish-scale attached to the lug, the target value is 2.375-3.75 lbs.

Toyota needs to make this more clear in the FSM.

i'm not following.

The 9.5-15 lbs is NOT lbf - it's not torque, it's lbs on the spring scale when pulling on a lug in te top center position. It's not the torque to be applied to the adjusting nut.

or are you equating the bearing torque with the torque applied to the adjusting nut? I don't think they are the same or comparable.

could you elaborate?

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[TrekboxX]

Oh, boy! See my point? Confusing as heck. I know it's the specified value for the spring scale, but I don't think your math is right. Moment = force x distance. So, if it's true that the 6-15 lbs on the spring scale is supposed to be measured on a 12" arm, then to get the same moment with a ~3" arm you would need to multiply by 4! So you'd need 24-60 pounds on the spring scale! From my experience that would give about 125-300 lbs of tq on the nut. "Yikes!"

I think until I can get a definitive answer I'm going to adjust them by feel, screw all the rest. I know that's how many mechanics do it, and we really don't have that many catastrophic failures (at all).

 

[hankinid]

Spring scale is not measuring torque, it's measuring rolling resistance.

When I use the scale, tigntening axle nut to get FSM spec with the fish scale gives me what I would expect to be standard torque for a wheel bearing...which equates to the same axle nut tightness I get using the FSM torque requirements.

I'm used to tightening front end bearings until I feel a bit of rolling resistance with a freshly lubed bearing, and then backing off the nut to the nearest flat or cotter pin hole, depending on the vehicle...

The bearing assembly is the same as any other car/truck...don't see the importance of the scale, but I do use it...I doubt there'd be an issue by simply using the FSM torque numbers without the scale...

Am I missing anything?

Steve

 

[TrekboxX]

The confusion is widespread!

Spring scale is not measuring torque, it's measuring rolling resistance.

Yes, and no. It's not torque on the axle nut, but it is measuring the "torque" required to turn the hub on the bearings, so it is one of two bearing "torque" measurements.

When I use the scale, tigntening axle nut to get FSM spec with the fish scale gives me what I would expect to be standard torque for a wheel bearing...which equates to the same axle nut tightness I get using the FSM torque requirements.

So, are you saying that the ~6lbs on the axle nut gives you 6-15 (or 9-15 I forget) lbs on the scale? I was nowhere near that, nor were many others. See threads linked on pg1. My understanding of the fsm is to start with ~6 lbs and adjust (increase) until 6-15 lbs is needed on the scale to measure "rolling resistance."
This sounds great, until you actually realize you need 35+ lbs to get into the lower spec range. This makes me think something is amiss.

I'm used to tightening front end bearings until I feel a bit of rolling resistance with a freshly lubed bearing, and then backing off the nut to the nearest flat or cotter pin hole, depending on the vehicle...

This sounds as good as any method...

The bearing assembly is the same as any other car/truck...don't see the importance of the scale, but I do use it...I doubt there'd be an issue by simply using the FSM torque numbers without the scale...

Am I missing anything?

My sentiments, exactly.

Steve

 

[TrekboxX]

I did that wrong, but my response is in the above quote.

 

[hankinid]

I did that wrong, but my response is in the above quote.

So I'm thinking I'm OK...right?

Steve

 

[SupraTuRD]

Sorry about the miscalculation... It was a long day. =]


The FSM procedure seems right up until the preload measurement is taken at the wheel stud. The 3-4 lbs of drag by the fish scale that everyone is able to achieve by following the FSM procedure sounds reasonable for a preloaded wheel bearing... not the 9-15 lbs that everyone is trying to attain. I'm convinced that the "9.5-15.0 lbf" specification is a typo.

The preload measurement at the stud has no lever factored into it so the FSM shouldn't show "lbF". Once the "F" is in the equation, that becomes a measurement at 12" radius, not 3" as the FSM shows.

 

[elkaholic]

Actually, in some circles, kgf and lbf mean Kilogram-force or pound-force as opposed to mass measurements (kg or lb sometimes (ok rarely) stated as kgm or lbm). I don't recall the bolt circle diameter off the top of my head, but let's say 3" for argument sake, then 12 pounds and 3" would equate to 3 ft-lb of torque.

The difference is lbf to ft-lb... the metric is usually stated as kg-m (or kg-cm)

yeah, I probably just made the confusion worse .....

 

[TrekboxX]

Makes sense. I was looking at it backwards. Had it in my head that the torque was the typo, not the preload. Good call.

 

[TrekboxX]

Actually, in some circles, kgf and lbf mean Kilogram-force or pound-force as opposed to mass measurements (kg or lb sometimes (ok rarely) stated as kgm or lbm). I don't recall the bolt circle diameter off the top of my head, but let's say 3" for argument sake, then 12 pounds and 3" would equate to 3 lb-ft of torque.

The difference is lbf to lb-ft ... the metric is usually stated as kg-m

yeah, I probably just made the confusion worse .....

Perhaps! That's new to me that they are different. I thought the difference was between lb-ft (a vector product, normally used to measure tq) and ft-lb (a scalar product), and also to be confused with psi!

So, I guess we should be measuring the starting friction or stiction with the spring scale on the lug in ft-lbs, but switch to lb-ft for rolling friction. The adjuster nut would be tightened in lb-ft of torque, to achieve the proper psi of the roller bearings against the races. We should add in the effect of the coefficient of friction differential between dry and greased nuts and washers... Oh, boy! I think I'll just wing it

 

[michaelshin]

Perhaps! That's new to me that they are different. I thought the difference was between lb-ft (a vector product, normally used to measure tq) and ft-lb (a scalar product), and also to be confused with psi!

So, I guess we should be measuring the starting friction or stiction with the spring scale on the lug in ft-lbs, but switch to lb-ft for rolling friction. The adjuster nut would be tightened in lb-ft of torque, to achieve the proper psi of the roller bearings against the races. We should add in the effect of the coefficient of friction differential between dry and greased nuts and washers... Oh, boy! I think I'll just wing it

I think I will measure the torque with fish scale after removing just the outer nut to see where it's at for reference. Does this mean anything?

 

[TrekboxX]

By torque you mean rolling resistance measured at the lugs? Sure, may be good to know where you were at. Doesn't mean you'll know where to go...

 

[Norcalfamily]

By torque you mean rolling resistance measured at the lugs? Sure, may be good to know where you were at. Doesn't mean you'll know where to go...

Yes.
Isn't the resistance where people are having trouble?

 

[TrekboxX]

Yes. See beginning of post- the torque required to get the fsm specified resistance is seemingly too much, or vice-versa. Post up your findings!

 

[ENGINE er]

Just wanted to add my experience. Did wheel bearing and didn't have a fish scale, and didnt properly lube the axle shaft needle bearing. The truck would reverberate from 50-70mph.

Tore down the front end this morning, re lubed the needle bearings, picked up a fish scale and set both to 15lbf. reverberation is gone and she is silky smooth. I was really worried I was going to have to rebuild the front diff. Start to finish the job took 2 hours.

 

[SupraTuRD]

The truck would reverberate from 50-70mph.

Was this load sensitive? Acceleration? Deceleration?

 

[TrekboxX]

Happy turkey day. If you bend the tabs on the washer correctly, it shouldn't come loose. Good luck, let us know.