Tuesday, June 26, 2012

Jackass Award - GM's Theta-platform Front Hubs

2005 Chevrolet Equinox
This is a 2005 Chevy Equinox, one of a trio of first-generation Theta platform mid-size crossovers that General Motors sold in North America, the others being the Saturn Vue and Pontiac Torrent. The Spring Hill, Tennessee-made Vue came first, introduced as a 2002 model, with the Ingersoll, Ontario-made Equinox and Torrent following in 2004.

Seen below is the front hub assembly from the Equinox pictured above; a Torrent would be identical, a Vue similar. Incorporated into the hub is the front wheel bearing, which is a wear item, and a common failure part in many vehicles, though I can safely say that it's a particular weak spot in numerous GM vehicles. When the bearing portion of this part fails, it can result in excessive play, noise, or both. This one was noisy.

Front Hub Assembly - Before
So why is this worthy of a Jackass Award? Well, it's not for the failure rate, which, to be fair, may or may not be statistically significant - my sample area includes a higher than normal percentage of GM vehicles, after all. Not for using a hub design, which while more expensive to replace, is far, far easier to change than the press-fit wheel bearings frequently found in such applications.

No, the Jackass Award goes to the engineering team for this part, who obviously felt that it was not only a good idea to fit a steel hub into an aluminum steering knuckle (steel and aluminum don't play well together, especially in the presence of salt), but to do so with NASA-level tolerances that made this part a tight fit even before the swelling effects of corrosion became a factor. The bolts are what actually hold the hub in place, and there are several other vehicles where there is clearance or even cutouts around their hubs, so this one-step-short-of-press-fit design was unnecessary.

The end result is a hub that is remarkably reluctant to part ways with the knuckle. So reluctant, in fact, that it normally has to be beaten to a pulp to be removed. (The rear hubs on these vehicles don't exactly fall out either.)

Forget using a slide hammer here, as that will just pull the flange out of the bearing. The most effective extraction method, short of removing the knuckle/upright and putting it in a press (which no sane mechanic would want to do), is to baseball-style swing a Bloody Big Hammer at the flange until the hub and knuckle declare defeat, or the mechanic passes out. You can see what the hub looks like after 15 minutes of intermittent hammer swinging in the photo below.

I did mention the aluminum knuckle, right? Be careful not to hit that with the BBH - it's not really forgiving if you hit it in the wrong places. It's not unusual for the sheetmetal dust shield to suffer during this process, either. If it isn't rotten already. Don't worry, the dealer stocks it; you won't be the first to kill one.

Extracted Hub - After 15 minutes of on-and-off pounding, it's feeling a bit out of shape...

You'd think that a vehicle designed in North America and built in Canada would take corrosion into account. As you can see below, corrosion is definitely a factor here. (The machined face of the knuckle has already been cleaned in this photo.)

See the corrosion?
Oddly, the nearly identical component set in a similarly-sized Chevy Uplander minivan does not suffer from the same problem. Yes, it fails regularly, and it does use an aluminum knuckle with a steel bearing, but it normally comes apart with little fuss.

For designing a serviceable part in a manner that makes it far more difficult to actually service than it ever needed to be, while simultaneously failing to take into consideration the real-world environment that this product would face in its primary market, please accept a Jackass Award. A great example of Bonehead Engineering.

...and here's what the new unit looks like. I couldn't leave you hanging.


  1. Thanks for publishing this. Nice work.

  2. Thank you for writing about this car repair problem. Earlier I was helping a neighbor in attempting to remove the front wheel bearing from a 2004 Saturn Vue. We got all the required bolts out and expected the hub to break free with a little tapping of the hammer. Au contraire... After using an air hammer with a chisel tip all we have accomplished is to gouge the surface of the aluminum steering knuckle. Knowing how badly aluminum and steel can corrode at their junction, I figured there would be a bit of corrosion in the "bore" in the aluminum steering knuckle. Your photo has illustrated the true nature of the problem... there is a TON of corrosion!

    I took an interest in my neighbor's car problem because I own a "cousin" to his Saturn... a 2006 Chevy Equinox. At almost 100,000 miles I have had only a few problems with the vehicle. But I'm not looking forward to replacing the wheel bearings when they croak.

    Again, thank you for sharing your trials and tribulations. Well-written content with photos is bound to be helpful to people all over the world, and for years to come. Keep up the good work.

    Bruce Maki

  3. Thank you for calling out the morons that are so smart their stupid.

  4. I've been at it 5 hours now and it still hasn't come off.

    1. Thats why the shop want $350 to do one

    2. Many years ago I was a mechanic and couldn't figure out why it was so hard to service vehicles. Later in my career I became an automotive engineer and worked for over 30 years doing product development. Generally speaking, there is little if any consideration given to difficulty of repairs other than basic maintainence. This is because cost and ability to put vehicle together are priorities, service is last on the list.

      Although it is extra time, removing the whole steering knuckle and using a hydraulic press to remove stuck hub is probably your best bet. Pounding away for hours with a sledge hammer might be doing more damage than you think.

      I am actually working on my wife's vehicle now and giving up on getting hub off using a slide hammer.

    3. My wife has a 04 saturn vue. She has owned the vehicle for almost 4 years and we are going on our 4th set of unit bearings to go one the vehicle. Due to the difficult nature of separating the bearing from the knuckle several shops had used the beat it out method and now we have a bent knuckle causing premature bearing failure. And not one single shop used anti-seize. Due to the condition of the knuckles no shop would warranty the work.

  5. I am about to do this job on the wife's 2005 Equinox. The driver's side is bad, and wanted to do the pass side while there. I noticed earlier if you remove the studs, an M12 bolt with a flange nut backed up against the flange could be used to press against the knuckle, 3 bolts can fit around the hub. Do you guys think this might work? And maybe using a torch to heat the hub? I hate swinging Bloody Big Hammers... Thoughts?

  6. Just a follow-up for those who might be interested. Using the M12 bolts worked well. I could only fit two against the knuckle. I held the bolt still and turned the flange nut, this kept the bolt from digging into the backing plate. I would tighten the nuts to put some pressure on the hub, then tap around the edges of the wheel flange with a small hammer and it would slip out bit. Rinse & repeat. Once setup, this only took a few easy minutes to remove the hub. This is the drivers side, and as the bolts are slightly of from the front, I needed to tap that side a bit more to have it come out evenly.
    What really annoys me is the hub opening isn't quite large enough to allow you to remove the CV driveshaft assembly. I wanted to replace that while I was there, and was hoping to avoid disturbing the ball joint. It's the boot clamp that doesn't fit through!

  7. I am about to change the Hub Assembly, do you know what size nut that is in the center. I am borrowing tools and only want to ask once.