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RE: Online torque specifications

To: "Randall Young" <>
Subject: RE: Online torque specifications
From: "Randall Young" <>
Date: Wed, 2 Jun 2004 23:54:26 -0700
> Any idea why you can't use an impact wrench to take them off and
> how does it
> ruin the wheel bearings?  Just curious.

On this FWD design, the outer stub axle penetrates through the center of the
unitized double row bearing/hub.  Thus, all the clamping force of that nut
(which BTW my Chevy book says should be torqued to 225 ftlb) is applied to
the inner race.  Since the bearing is quite loose before the stub axle is
torqued down (and the book warns not to move the car in this condition), the
race evidently deflects a good deal under the clamping force, possibly even
applies preload to the bearing.

I'm not certain just how, but it appears that there was enough impact
transmitted to the inner race to cause it to spall against the bearing
balls.  At least that's what I saw on the one I cut apart, where I had used
an impact gun to run the nut onto the shaft.  (It's a deformed thread
prevailing torque nut and has to run almost 2" up the shaft ... yes, I'm
lazy :) Even though I didn't run the nut home, it still apparently ruined
the bearing.  On the other side, I only used the impact gun to remove the
nut ... it lasted more like a year as I recall, but still failed.  Didn't
bother cutting it apart, just went by the book when replacing it and never
had another failure.


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