Wheel bearing diagnosis

[DAlgie]

I had a thread going on here erlier about rear cv removal. The thing ended up having a dead rear wheel bearing, BIG time noise, so loud at freeway speeds that it was deafening. ANYWAY, I finally got the bearing out of the rear hub carrier/ upright. I have done a lot of race car wheel bearing diagnosis, we work our Indy car wheel bearings very hard on an oval. Subes tend to have whel bearing problems, yet nobody can figure out what the real problem is. My diagnosis is that the bearing is sized properly for the loads it sees, the package seems to be well suited for the load. it is a double ball angular contact bearing that I think is very nice, well engineered. When I pulled it apart my first thoughts were that it either had poor quality grease, or too much preload. I doubt that the problem is just unsuitable grease. Therefore it has too much preload. HOWEVER, when I went to press the outer race out of the carrier, it took many tons to move, far more than normally needed. This means that the bearing fit into the carrier is too tight, this will shrink a thin walled race down in size, and force the preload on an angular contact bearing to be too high. Subaru, if you read this, please look into what interference fit the bearing manufacturer reccomends for this bearing package. I believe you are out of their spec on this.

[Scottbaru]

Large bearings can take a pretty substantial interference (press) fit. I haven't been in these subaru hubs, but it sounds like the press-fit is all that holds the bearings in place, no fasteners. I'm new to Subarus, and dissapointed that I might have ball bearings in my hubs instead of roller bearings. Do Indy cars have ball bearings in their hubs? Wheel bearings I'm more familiar with are tapered roller bearings, a pair of single rows are usually tightened toward each other, setting a preload. The double-row, angular contact ball bearings I've used can't be preloaded in the normal sense The two rows share solid inner and outer races. I design and build automated industrial machinery as a side job, I specify (from bearing manufacturers specs) fits for my machinists, and press in a lot of bearings myself when I can. Usually it's bushings that have trouble with tight fits compressing them.

[sea#3]

There is an update for the wheel bearings and couple of precoutions , info at endwrench http://endwrench.com/images/pdfs/WheelBearing.pdf

 

The one thing they dont mention is the seal surface area on the outer c/v , if it is rusted at the seal surface , this can cause water to get into the wheel bearing and cause a failure

 

hope that helps

SEA#3

[DAlgie]

No, there is a retaining ring that holds it in there. It presses up to a shoulder, and then you fit the ring. Really, I have a lot of experience with bearing fits, this one is too tight. Quite possible that this one is on the low end of the tolerance, but that also means that the range is too large, or all are low in the range. From the problems they have, I would bet the range is on the low side to begin with. This car is a 2001, 68k miles, everything else on it is in really nice shape, I have owned it since new and it's never been abused or hit a curb. No water was present in the bearing, and the seals weren't leaking grease out.

[DAlgie]

Indy cars use different bearing packages from year to year, common was a combo twin angular contact like this, with a plain needle roller as well, older cars had twin tapered rollers, problems with those is they are very touchy with preload, much the same as the angular contact package bearing, but those, like this Sube bearing, have preset preload.

[Scottbaru]

twin angular contact like this, with a plain needle roller as well, older cars had twin tapered rollers

Those setups sound much more rugged than just the double ball-bearing. I imagine the Indy cars don't run very many races with the same bearing set, probably one race?

 

I see your car takes Timken bearing 511023, 38mm bore and 65mm OD. I don't see tolerances for press-fits in their online catalog. I suspect that number is an industry standard, I can find it if I search around or when I get back to work, If you want to measure the hub bore. How deep does this bearing have to be pressed in? Comments I've read make it sound fairly deep. The bearing can really get hot if you're pressing into a deep bore, some people use lube, I usually clean it well and use bearing locker, which seems to lubricate a bit. I put most of my bearings into aluminum, pressing them dry seems to build up shavings in front of them, which gets really tight in a deep press. Should be better with steel, but it could still build up some material.

 

I've read here you can put a different bearing in the Impreza, maybe from the Legacy? Are those roller maybe? I guess you could take the bearing dimensions from Timken and try to find something better to fit. Next year I'll probably have an uncontrollable urge to repack or replace my wheel bearings at 100k miles.

[DAlgie]

Yes, we run just one race with the bearings, don't always replace them though, just a clean, inspect and regrease. I think these right now run maybe 1200 miles before we pitch them. A bearing of this size (The Impreza) pressed into cast steel, it's quite a wide bearing, I would give it maybe .0007" to .001" interference fit, I didn't measure this one, it's back together again, but I would guess it had .0025" to .003" interference, way too much in my book. You can get away with more with a heavy wall outer race bearing, it will not shrink down from the housing it's pressed into, but this has a thin outer race and the housing is thick, so it will command the OD of the bearing to whatever the fit is. I'm hoping that me pressing the old one out and pressing a new one in has burnished the bore slightly, and now has a little less interference. It did go in easier than the old one coming out for sure. A twin tapered roller will withstand more preload, but that's not a fix for too much in the first place really.

[Scottbaru]

If it went in easier than out, maybe it was originally assembled with bearing locker? I'd expect it, since they rely on friction to hold it in. I'll definitely use high-temp bearing locker if I ever renew mine. I guess I need to wait 'till they're howling, sounds like they can't be repacked.

[DAlgie]

This had no Loctite on it at all, you can always tell if there's any there. I would not use Loctite, this will only increase the bearing fit, the absolute last thing you want in this case. Just assemble the new bearing in it's bore with gearbox oil to lubricate it going in. You can regrease them, but the work involved is a real pain in the rear, for about $110 per wheel, I'll put new bearings in, especially if you have 100k miles now. This old bearing went through the hard chrome, yours might be getting there now, and you would never know it. New grease only might delay it, but not by that much.

[Scottbaru]

I've looked up your and my rear wheel bearings on Timken, here's the comparison:

 

Car: '01 Impreza

Bearing type: Ball Bearing

Timkin #: 511023

Width: 52mm

OD: 65mm

Bore: 38mm

 

Car: '99 Legacy

Bearing type: Double Row Tapered Assy

Timkin #: 513248

Width: 51.938mm

OD: 64.994mm

Bore: 37.996mm

 

Mine lists part#1 and part#2 as 513248, so maybe mine takes two bearings per wheel, but it appears the dimensions are for the assembly of two. If so, I think the Legacy bearings should fit the Impreza. I only have these dimensions, I'd prefer dimensioned drawings catalogs usually have to be more certain. What do you think?

[DAlgie]

Yeah, I would have thought that both cars are the same. See if you can find out what the '01 Legacy uses, wondering if it also is a ball, meaning that they went to ball, away from tapered roller, which is a shame. The dimensions you list there, the Legacy numbers are probably converted back from metric, and are actually the same. Bearings are always full millimeter sizes, and are almost always metric. Anyone have any info on the tapered rollers failing?

[Olnick]

meaning that they went to ball, away from tapered roller, which is a shame.

 

This is fascinating stuff, guys. I'll probably never touch a bearing in my life but I'm learning so much. The "essence" of an automobile is that it can move us from A to B. If it can do so with the least rolling resistance it is simply so much more efficient and useful to us. I've always felt that good bearings are the heart of an efficient, useful tool--in this case, a car.

 

Egads, I'm writing an Ode to a Bearing! Forgive me, but the topic really grabbed my interest.

 

DAlgie, your comment above intrigues me. Why do you think tapered rollers are better?

[DAlgie]

A tapered roller is a higher capacity bearing than an angular contact ball. if you think about it, the tapered roller has a lot more contact area, and the roller runs in a perfect circumference, with no scuffing at all. The angular contact ball has small contact area, and the edges of the contact area are at a different circumference to the middle, some differences in contact speeds are seen, hence the slight scuffing.

[Scottbaru]

Tapered use cylindrical roller bearings instead of balls. Tapered means the rollers are angled, so they look like they'd run on a tapered shaft.

[sea#3]

Yeah, I would have thought that both cars are the same. See if you can find out what the '01 Legacy uses, wondering if it also is a ball, meaning that they went to ball, away from tapered roller, which is a shame. The dimensions you list there, the Legacy numbers are probably converted back from metric, and are actually the same. Bearings are always full millimeter sizes, and are almost always metric. Anyone have any info on the tapered rollers failing?

 

 

Subaru has also authorized the

 

 

installation of a taper roller-type

 

bearing, part number

 

28016AA030, as the replacement

 

part on the applicable Impreza

 

and Forester models. This taper

 

bearing is the same bearing that

 

is applicable to 1999 model year

 

and prior Legacy models.

 

If you have diagnosed a failed

 

rear wheel bearing, repair it with

 

the new procedure and check the

 

condition of the remaining side.

 

Replace only if needed.

 

The new genuine Subaru rear

 

wheel bearings are not to be

 

packed with grease of any kind.

 

The bearing is ready to install

 

out of the box.

quote from endwrench

 

SEA#3

 

 

[Olnick]

Thanks DAlgie and Scottbaru, appreciate the explanations. Makes sense to me that the tapered roller is a higher capacity bearing, but doesn't the greater contact area imply more friction or resistance as compared to a ball?

 

How big are the rollers in Subie bearings anway (length, end diameters)?

 

I agree the "scuffing" of an angular contact ball sounds bad. Is there some benefit (or logic) to designing a bearing with angular contact? What would be the alternative--parallel contact faces?

 

Thanks again for indulging me guys.

[DAlgie]

The tapered roller does have parallel contact faces, it's just that they have tapered surfaces (and rollers) to make up for the circumference difference so there is no scuffing. Take one apart and study it, you'll see how it all makes sense.

[Scottbaru]

I see in '00 the Legacy changed to a four-bolt flange, double roller bearing, with a pilot ridge to center it and carry the hub. I doubt you could use the old bearing as apparently you can with the Impreza and Forsester.

 

 

I wonder about sourcing that bearing with the industry numbers, you can usually specify a few kinds of grease or oil.

 

I suspect the bearings are slightly undersize on purpose. A lot of parts I order are slightly under or over nominal size for press-fit or slip-fit. Perhaps Subaru wanted to use the same hubs with slightly less interference fit? Or the bearing makers recognized a need and made an adjusted fit bearing?

 

Oddly, my Landcruiser uses a metric and an inch tapered bearing opposing each other in the same hub!

[Setright]

Olnick, I believe the idea with angle contact speherical bearings is encourage it to self-center, and reduce rattling.

It also allows it to deal with axial forces. Like when cornering.

[Olnick]

Well shoot, Setright--certainly sounds reasonable to me! Thanks.

[Scottbaru]

I'd rather have roller bearings than ball bearings, but ball bearings are usually cheaper.