Unscheduled maintenance on a second-generation Prius?? Unthinkable!
With about 190,000 miles on mine, though, one needs to accept the idea that anything could happen. In this case, it was a front wheel bearing that decided it had taken enough pounding for one lifetime. This leadup text is largely lifted from some posts I made to the Prius_Technical_Stuff yahoogroup while tracking the progress of the issue over the course of a week or so. I was on the way to visit relatives over the holidays, and realized about a third of the way into the trip that the right front wheel bearing was definitely on the way out. More groaning when I turned toward the left, and as it developed further when I stopped to check it I could feel a tiny little bit of play when shaking that wheel in and out at the top. Definitely toast, nothing really for it except replacement. This bearing probably didn't owe me a dime at this point because I had frankly put it through hell, but on the first leg of a long roadtrip was sort of an inconvenient time for it to start failing for real. Oddly, the standard bearing check of jacking the wheel up and trying a top-to-bottom shake *didn't* let me feel any play, which is one reason I started the trip on that bearing in the first place -- I had suspicions maybe a month before and did that test and it felt fine, so I assumed the bearing was still good. Now that I was more sure about its condition, I still found it odd that *only* with the weight of that corner of the car on the bearing and using the momentum of the rest of the body as I shook things in and out could I feel any sort of thunking. So it certainly wasn't totally shredding itself inside yet. Given that popular wisdom seemed to hold that one could ride fairly far on a bad wheel bearing, I managed to nurse that sucker for another 1000-plus miles after starting to really hear/feel it through the floorboards and steering wheel, doing periodic side-play checks to make sure it wasn't about to fall off, and got where I needed to be. Fortunately over fairly flat and straight interstates. The long wandering road-trip involving mountains I was hoping to turn this run into was kinda off the table by now, but at least I was still rolling instead of stranded in south bumfuk somewhere. I even managed to record what I was hearing in a short video (MP4, 1 Mb, ~7 sec) -- the steady tone that's about a G2 on the musical scale is the sound in question, and I could make it come and go a little by gently swaying the steering back and forth in the lane. As the stories of Prius owners trying to replace their own front bearings are in the nightmare class and various special tools and possibly presses are needed, I decided to let the local "stealership" do this one. They got off on the wrong foot with me right up front by suggesting that my suspicion of a bad bearing might be wrong and they'd need me in for a "diagnosis" visit first, and then another visit to actually do the work after ordering and receiving the parts as wheel bearings generally aren't stocked at dealer parts departments. After expressing that I didn't really enjoy being talked to like an idiot and maybe they should find me somebody who isn't afraid of knowledgeable clients, we started the conversation over and they finally clarified the logistics of what they wanted me to do, and then scheduled the diag appointment a couple of days out. I did a little reading through the service-manual procedure for replacing bearings and figured that with the right tools it should be a fairly straightforward fix, if they don't screw up the delicate dust cup inside the steering knuckle or mess up the suspension alignment. The car had *never* been aligned the whole time I've had it other than a minor rear wheel tweak using Bob's shims years ago, so it would be interesting if they followed the recommended procedure of a full alignment after having some the suspension apart. Before heading for the dealership I popped the wheel and rotor off and had a look at the area, just to make sure there wasn't any collateral damage or signs of heating or any of that. Still no discernible hub play with the weight off the wheel! The CV boots were in good shape -- that was one thing I wanted to make sure of, and having a fresh look at the rest of the area would limit the scope of what the dealership could legitimately try and tell me was "bad". I could definitely see evidence of corrosion between the aluminum knuckle and the hub piece, which according to the stories tends to glue them together almost as one piece, so I expected Toyota would have a bit of similar trouble separating the two. The brake shroud in between might be a loss as well, being caught in the middle of the assembly and fairly rusty. But in general I've kept things fairly clean under there so maybe that would make their lives easier. Worst case, they'd get me a new knuckle *and* hub and then they would only have to worry about the balljoint and suspension attachment bolts. After spending a summer dealing with a bunch of construction planning on the house, including research into what kinds of fasteners to use with different materials, I have to seriously wonder -- when aluminum parts used in auto manufacture are in contact with steel parts, why aren't said steel parts galvanized?? Having that would allow steel be in much closer proximity to aluminum in wet environments and not instantly turn into a self-destroying battery. I.e. the automakers need to look up "galvanic scale" and design their surface treatments accordingly. I would have only this one bearing replaced, playing the odds that one failure is often an anomalous fluke and the rest of them were still good for the longer haul. Despite tempting thoughts of changing both fronts, collective experience seems to indicate it doesn't make sense to replace any more bearings than the failed one even at fairly high mileage. Not to mention additional cost. So off I went to the dealer, and pulled in next to the "fishbowl" where all the service-writers hang out. One of the techs passing by stopped with a pretty serious double-take and started eyeballing the car, so I gave him a website flyer. The service writer seemed curious so I gave him one too, with encouragement to distribute it around. The paperwork mill involved the usual warnings about the various outstanding recalls like the steering shaft and hybrid water pump and floor mats, with me going "decline, decline, decline" all the way through. This car never even got the ECU reflash for the supposed "stalling" problem way back when, and I reassured them that I was well aware of all these conditions and in the interest of science [not to mention keeping their mitts off my car as much as possible] was deliberately not following up on any of them. They finally got me checked in, and whisked the car away into the holding-pen lot out back. Except that they'd also taken my backpack with it, and I had to have them walk me out there to fetch it. About 20 minutes later the SW came to find me and said that yes, my diagnosis was right on the money, and better yet they actually *had* a new hub in stock and if I was willing to hang out at the place for another 2 or 3 hours they could have me fixed up and back on the road that very afternoon. Great, I said, let's do it! I didn't need to be anywhere specific that day and I'd brought my own entertainment along with me. They said they'd put "their best guy" on it, but I bet they tell that to all the customers. |
Figuring things were probably in good hands, I found myself a little table in their waiting room and sat down at the laptop to work on more of my house story. After a short while I wandered back out to the fishbowl to have a look, and it was immediately clear that the whole steering knuckle was already off the far side and being worked on at the bench. |
The little mystery was solved by finding a relevant section in a service
manual, and confirmed with a brief chat with a support guy over at Timken.
He was cordial and they've got a lot of good info on their website. [What
I didn't think to inquire about was the relationship between Timken and
Koyo other than both appearing in the leadoff picture here]. This is
probably a generic diagram, as the specific bearing configuration in the
Prius is clearly a little different.
Nonetheless, the "Special Service Tool" here is just a big-ass bolt and nut that substitutes for the missing axle shaft coming from the CV joint, and prevents the bearing from separating under load. When assembled into the car, the splined axle shaft has a wider shoulder up against the inside cone of the bearing [where the bolt head is here] and the big "jesus nut" on the end of the axle holds the whole thing together. This, said the Timken fellow, is why the axle nut torque is so important -- the bearing has to have the right preload to maintain zero play, but not get so squashed down that it starts binding. So the whole key to retention is the axle nut, which gets staked in place after torquing to make sure it can't back off. This still amounts to 150 foot-pounds, which is like twice the torque applied to lug nugs. That's quite a lot, and why special big-ass wrenches are needed. |
And now you get to examine my balls. Well, er, you know. I could see
no difference at all between my samples from the inside race vs. the
outside one, so these are clearly the hardest metal in the assembly and
hadn't experienced any wear.
Ooh, shiny. The reflections are amusingly Escher-esque, with my camera lens and hands in prominence and the house, car, and driveway surrounding -- but on a much smaller scale. And the reflections of the reflections of the *other* ball would theoretically have an infinite progression. |
The cones and races were a different story, however. After cleaning off
the cone [and putting a nasty slice into my thumb when that sharp flange
slipped, grrr] the spalling was obvious. In the race I wiped down into
the cage where I'd popped the ball out and uncovered more roughness
there too. Textbook metal fatigue. But what caused it??
I would encourage a critical look at the failure-analysis documents found at Timken's web site in the light duty automotive area. My guess would start with water ingress leading to corrosion, but it could also have been accompanied by some abrasive contamination from all the dust encountered in my various out-west roadtrips including pounding down lots of gravel roads in Death Valley. This may not have particularly good implications for any of my other bearings, but I can fervently hope their seals are all still unbreached. |