Tuesday, April 1, 2014

Hidden dangers in one-piece hubs


Another day, another brake job . . . but not so fast!

Take a look at this rear hub/brake assembly. It's a pretty typical worn out pad and rotor picture, one that we've addressed with a cleanup and new brake parts a thousand times before.  This one turned out different.



Thanks to Land Rover master technician Paul Ferreira for spotting a very subtle flaw.  Once the brake rotor had been removed, Paul noticed the wheel studs were not quite the same length. Take a look at what he saw, and see if you pick it up.  It's a small enough thing that I'll bet 99% of technicians would not give this a second glance.


Knowing that something was wrong, he looked a little harder.  Here's what he found.  I've put arrows and text on the photo to point the problem out:


It's kind of scary to think that the heads were popped off of three of five wheel studs on the right rear of this 2002 Range Rover.  Why did that happen? I have no idea, other than accumulated stress.  Why this wheel and not the others?  I don't know that either, maybe just luck.

The studs must have been broken for a while, because the lugs were all tight even though some were pulled halfway through the hub.  Presumably they pulled a little farther every time a wheel was torqued into place, and they would have eventually gotten to the point where they'd have given way, perhaps suddenly.

The moral of this story - check the wheel studs whenever they are exposed for service.  Sometimes part like this - bits we think of as permanent - really aren't.

(c) 2014 John Elder Robison

John Elder Robison is the general manager of J E Robison Service Company, independent Land Rover restoration and repair specialists in Springfield, Massachusetts.  John is a longtime technical consultant to the Land Rover, Mercedes, BMW, Porsche and Rolls Royce Owner's Clubs, and he’s owned and restored many of these fine vehicles.  Find him online at www.robisonservice.com or in the real world at 413-785-1665

2 comments:

gsmac said...

Interesting. Do you think it could have been a lateral impact (i.e. sliding back end into a curb), or just a trigger-happy wheel jockey torquing lug nuts far too tight with his impact wrench?

John Elder Robison said...

gsmac, those are both possible answers, and I thank you for good suggestions. The car has 260k miles on its odometer and I wondered if it was simple metal fatigue but your ideas may make more sense.