Loose SKF rear wheel bearing

burgermeister · burgermeister's Garage

I purchased an SKF rear wheel bearing last fall & installed it. After my 1st track day, I failed the next Tech Inspection for a loose rear wheel bearing. I replaced it with a spare FAG bearing.

I took the SKF bearing apart - everything looked dandy, grease was clean, no pitting or even discoloration of the metal. It was just loose. Preload was OK - I checked the axle nut torque before I took it apart.

Anybody else run into this, or did I just get the lucky tolerance stackup?

Is it just me, or are German replacement parts just not what they used to be?

KTL · 06-20-2011, 03:11 PM

Yeah some parts aren't what they used to be. But something from SKF should still be decent quality. You sure you didn't damage it when you installed it? It's easy to damage a new bearing if you don't press it in well and pull in the stub axle flange properly.

How did you take the failed bearing apart? You destroy it when you pull the stub axle flange from the bearing.

burgermeister · burgermeister's Garage

I pressed it in (the hub also) with the HF front wheel bearing kit. Frozen bearing, hot banana (na na na na na ... - Swedish Chef) arm. It actually slipped most of the way in with just hand pressure. The hub took a bit of force, but still went in nicely. The FAG replacement required pressing in, just for reference.

Removal took one side of the old bearing apart. I pressed the other inner race out on a bench vise. I always remove the balls anyway - they get recycled into steelie marbles for the kids.

Hard to make a warranty claim on a part that gets destroyed during removal ...

KTL · 06-22-2011, 07:31 AM

Agreed there's not much you can do to show the bearing failed, when you have to destroy it in removal mode.

Weird that the SKF slipped most of the way in but the FAG had to be pressed in. My FAGs all had to be pressed in, even with decent amount of heat applied to the banana arms.

hcoles · 06-22-2011, 07:42 AM

interesting that a new bearing had enough play to be felt by pushing on the tire, if you still have the parts you could put the inner race back on and see if you can feel any play, you might take the seals off and grease out and check as well, if it feels smooth with no play something else may be going on

KTL · 06-22-2011, 07:49 AM

Good point about the seals and grease. Many racers remove the grease from a new bearing and repack with high quality grease. Often times the failure of new CV axles and rear wheel bearings is the result of the economical grease used by the manufacturer.

eimkeith · 06-22-2011, 06:48 PM

We've seen it also - several in the last 2 years, in fact.

Bad run?

Steve@Rennsport · 06-22-2011, 07:57 PM

Quote:

Originally Posted by eimkeith

We've seen it also - several in the last 2 years, in fact.

Bad run?

Me too,.....I've chalked this up to outsourcing (very common) and loose QC.

FAG's are better, IMHO.

burgermeister · burgermeister's Garage

Disappointing to hear that it's not a rarity. Well, the FAGs are cheaper anyway ...
It's got to be really irritating if you're running a shop and you get rework through no fault of your own.

hcoles, I don't think you can check the bearing for looseness in an uninstalled condition (other than by disassembly and very careful measuring with tools I don't own). Pressing the bearing into the banana arm, pressing in the hub, and tightening the axle nut to 330 ft*lb all will tend to reduce internal clearances or add preload. A new bearing might be slightly loose by itself but be tight once installed. Also, one of the inner race halves has a big cut in it so I could get it off the hub ... and lord knows where the "marbles" have ended up.

That's one advantage of the bolt in hub/bearing combos many new cars have these days - the final assembly can be checked. The downside is more mass & increased compliance of the bearing assembly, especially the 3-bolt units.

hcoles · 06-23-2011, 06:30 AM

good point - the load from the axle nut would reduce clearances, would be interesting to calculate how much, from the sounds of things the quality issue would be obvious, I assume the issue is dimensional new and not because of wear. The Porsche rear bearing size is used on a number of different cars.

hcoles · 06-23-2011, 06:34 AM

using online clamping force calculator the clamping force is approx. 20,000 lbs. I hope there is an online deflection calculator.

hcoles · 06-23-2011, 07:21 AM

I couldn't resist. Back of paper bag calc.

Assume rim of the cylinder (inner cyl of inner race) area is 0.5 sq inches
Stress = 20,000/0.5 = 40,000 psi (clamping force is 20,000 lbs)
Strain = Stress/30,000,000
Strain = 0.0013 inches per inch
Assume both rims (two of the inner races) are 0.5" long

Compression = 0.0006"

So it would be interesting to see what the bearings feel like dry some play might be felt. The proper torque on the nut might be a key factor for bearing wear.

Good comment. Measurements of actual part are indicated.

suprxman · suprxman's Garage

Find a dedicated bearing supplier. I'm lucky that my town has one. If you have the numbers, bearings with numbers on them - anything the counter man can cross reference ( I have taken bearings for them to measure ) they can order new ones usually at a very fair price. Buy Timken and only Timken bearings. They will cost more but are worth it. IMHO.
Been doing this for 40 years.