New 914 rear wheel bearing, No to very little grease from manufacture Options

[Luke M]

So, I just purchased a set of New FAG wheel bearing (made in Germany) so I can install a set of the later (74-89) 911 rear hubs on my 914 control arms.
I saw a few you tube videos about how the bearings for the Boxster where being shipped with little to no grease in them. I figured before I install them to check the grease. Well sure enough one side had little grease and the other side had very little to no grease on the bearings. I should've taken a few pics but didn't have my phone handy. I still have another new bearing to inspect so I'll take pics of that one. I'm sure it will be the same way. Now to go pick up some grease and repack them.


So if anyone of you out there plan on replacing your rear bearing I would inspect them.

Here's a handy video which shows how to do this.

https://www.youtube.com/watch?v=l9P1R2clGAU

[Superhawk996]

@bbrock

Brent, I just want to be completely transparent that I'm not targeting you personally. I have no doubt that that one of your bearings had less lube than the others. Nor do I mean to question your mechanical ability or personal integrity. Your build is by far one of the most inspirational on this site and your attention to detail is an example for all of us to shoot for. (IMG:style_emoticons/default/grouphug.gif)

There is a saying:
Arguing with an engineer is like wresting a pig in mud, eventually you'll realize the pig likes it.


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My broader point in keeping this post going is that we all have limited time to focus on our projects. What we do with them is our own prerogative and we should all do what keeps us happy. My intent to the original post was to offer a perspective to the OP that bearings are in general pretty robust little pieces of hardware and that I personally wouldn't sweat them. Worst case is that one fails prematurely and we have to replace it. Things could be worse things in life.

As engineers we seek to design parts to a particular life cycle. Particularly the b10 life which is defined as:

"The measurement of the time by which ten percent of a population of a product will have failed. The term originates from the manufacture of anti-friction bearings, and is used to express the minimum lifetime of ninety percent of a given batch of bearings operating within speed and loading tolerances."

Whatever that life cycle is designed to be, the parts then have to be manufactured, and within that process, we shoot for six sigma capability which is defined as a bell curve, normal distribution where we want 99.7% of the manufactured product to meet the b10 life as produced. Getting rid of that 0.3% drives up costs exponentially.



The bottom line is that there will be some very low number of parts that don't meet the b10 life due to the process variation during manufacture. You very well may have had one of the 0.3% of parts that might fall below b10 life. Who knows for sure? I sure don't.

My broader point in all this was that ball bearings don't even need lubrication (IN THEORY). Lubrication just makes them last much longer and that the lubrication method is variable. Grease isn't even an ideal lubricant . . . ideally you would want just a light mist of oil continuously applied, especially at high shaft speeds. Grease generates too much heat and too much friction at high shaft speeds (talking 10,000+ rpm type speed here - not car axles). A nice oil mist is hard to achieve in practice in precision machinery and is impossible to have in a wheel bearing and would be incredibly maintenance intensive. Therefore grease is a pretty good compromise that lasts a long time and doesn't require much maintenance.

Going out to do some real work on the beast!

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