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Discussion Starter #1
Roughly a month ago I replaced my passenger front wheel bearing and the associated hub. shortly after I replaced the intermediate shaft bearing because noise persisted, and with a stethoscope, the mechanic found that was at fault. About a month later noise returned to my wheel bearing, and I had to have that replaced. The bearing had spun, causing it to bore the hub. Again, both were replaced. Immediately I heard noise from that bearing.....

Both have been FAG bearing: https://www.fcpeuro.com/products/wheel-bearing-6#fitment

the intermediate was: https://www.esaabparts.com/saab/parts/12785906

Any idea why these bearings are failing? As you can imagine the ~$200 for hub and bearing replacement over and over is tiring.
 

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No comment on the intermediate shaft bearing, as it might just failed.. but wheel bearing (was it torqued correctly to specs, of course ur mechanic will always tell u yes )
 

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Discussion Starter #3
No comment on the intermediate shaft bearing, as it might just failed.. but wheel bearing (was it torqued correctly to specs, of course ur mechanic will always tell u yes )
Do you have more information on the torque specs? Being that it is pressed in, I don't know what torque would be relevant.

the intermediate shaft is happy as can be.
 

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Oooh, without the proper torque applied on the bearing it will either be overstressed Or or under-stressed and the pressing forces wouldnt be enough to keep both parts of the bearing aligned parallel !!
If i have a rule in life about torque specs, its gona be (lug bolts, axle nuts, internal engine fasteners & any part that hold a gasket or o-ring)
 

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Discussion Starter #5
Oooh, without the proper torque applied on the bearing it will either be overstressed Or or under-stressed and the pressing forces wouldnt be enough to keep both parts of the bearing aligned parallel !!
If i have a rule in life about torque specs, its gona be (lug bolts, axle nuts, internal engine fasteners & any part that hold a gasket or o-ring)
I agree with the necessity of proper torque points, but my question is what is being torqued in this context. The bearing itself has no direct attachment to anything. Perhaps the bolts holding the hub was over or under its torque requirement?
 

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Yes of course it has attachment to both sides of the assembly regardless the enclosure is the bearing assembley or like in any other car the hub assembly , being pressed doesnt mean axial forces pointing perpendicular to the imaginary shaft through the bearing because of the vehicle weight are not in affect, they still are.
just try to loosen the other side nut and drive with it for a while.. ooh boy
 

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Discussion Starter #7
Yes of course it has attachment to both sides of the assembly regardless the enclosure is the bearing assembley or like in any other car the hub assembly , being pressed doesnt mean axial forces pointing perpendicular to the imaginary shaft through the bearing because of the vehicle weight are not in affect, they still are.
just try to loosen the other side nut and drive with it for a while.. ooh boy

I just want to be clear that the only controllable torque is that of the bolts holding the hub in place. The bearing itself has no torque applied when being pressed into the hub.

So with that in mind, maybe the hub's bolts where an incorrect torque? I don't know if that would cause the bearing to fail when leaving the parking lot. outside of there not being any bolts or something.
 

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During my 20 years with 9-5's I have seen premature bearing failure myself twice ...on one occasion the hub had been damaged removing the old bearing and the replacement failed in a matter of weeks.
The second time the driveshaft nut had not been torqued correctly.
 

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Discussion Starter #10
During my 20 years with 9-5's I have seen premature bearing failure myself twice ...on one occasion the hub had been damaged removing the old bearing and the replacement failed in a matter of weeks.
The second time the driveshaft nut had not been torqued correctly.
Thank you very much. I'm going to guess it was the driveshaft nut. I'll take my wheel off tomorrow morning and take a look. If its loose I'll have to give the shop a call.

Thank you for the help.
 

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checking if it is loose will not help. (if it is loose the bearing most probably is already destroyed)
the correct torque on the central nut adjusts the clearance of the balls to the housing of the bearing. Therefore it has to be the exact torque specified by the supplier. It is not a decision between loose or tight.
 

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However if it is loose then OP has cause to complain to incompetent mechanic who did the job!

I recently removed the hub nut cover on my sons Astra and the nut fell out!
I was livid!
 

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Also don't forget that the bearing must be pressed in properly, it must be pressed in from the outer race. Pressing in a bearing from the inner race will ruin the bearing very quickly.
 

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Discussion Starter #14
checking if it is loose will not help. (if it is loose the bearing most probably is already destroyed)
the correct torque on the central nut adjusts the clearance of the balls to the housing of the bearing. Therefore it has to be the exact torque specified by the supplier. It is not a decision between loose or tight.
I'm confident it's already destroyed. It's making the renown whirling noise of a blown bearing that I'm far too familiar with. Knowing whether it is improperly torqued will let me know if the shop is to blame. Although; it will not fix the broken bearing.
 

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I’d say overtorque happens just as much, if not more so, then undertorque. Guys hit that nut with the impact gun and not a torque wrench...
 

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I’d say overtorque happens just as much, if not more so, then undertorque. Guys hit that nut with the impact gun and not a torque wrench...
My dad used to crank down on the driveshaft nuts of his Hondas with a 3/4" breaker bar with the handle for his 2.5 ton jack slid over the end for extra leverage. I use that trick to loosen the nuts, but I can actually torque the driveshaft nut with my 1/2" torque wrench. It's near the end of its range, but I can get it to click. Back when the same driveshaft/hub nut was used on the NG900, the torque value was 290 NM or 214 lb/ft. I'm not sure why they went to a lower torque plus some number of degrees on the 9-5.
 

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My dad used to crank down on the driveshaft nuts of his Hondas with a 3/4" breaker bar with the handle for his 2.5 ton jack slid over the end for extra leverage. I use that trick to loosen the nuts, but I can actually torque the driveshaft nut with my 1/2" torque wrench. It's near the end of its range, but I can get it to click. Back when the same driveshaft/hub nut was used on the NG900, the torque value was 290 NM or 214 lb/ft. I'm not sure why they went to a lower torque plus some number of degrees on the 9-5.
Yeah, I suppose it’s all in what the bearing was designed to handle. I can imagine using the 3/4” breaker bar on a F350, but not a Honda! :oops:
 

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My bet is that the driveshaft nut was either not torqued properly or was not replaced. That nut is supposed to be replaced every time it comes loose.
 

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Yes it is important to torque the nut correctly, but I would attribute an immediate failure with the bearing being pressed in incorrectly from the outer race (as has been mentioned). I have damaged bearings myself doing this wrong, it does not take much force to ruin it. The pressing forces are pretty large, and it can be easy to use the wrong adapter that imparts force to the inner race by accident.

I would think an axle but that is too loose would cause a vibration or noise immediately, causing the op to check it out.

how confident do you feel with the mechanic doing to work?
 

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Discussion Starter #20 (Edited)
Yes it is important to torque the nut correctly, but I would attribute an immediate failure with the bearing being pressed in incorrectly from the outer race (as has been mentioned). I have damaged bearings myself doing this wrong, it does not take much force to ruin it. The pressing forces are pretty large, and it can be easy to use the wrong adapter that imparts force to the inner race by accident.

I would think an axle but that is too loose would cause a vibration or noise immediately, causing the op to check it out.

how confident do you feel with the mechanic doing to work?
After two failed bearings, not particularly.

Does anyone have find one brand favorable than the other for bearings? FAG or SKF? There's a substantial price increase to get the SKF, but I don't know if that means increased quality of any kind.
 
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