New 914 rear wheel bearing, No to very little grease from manufacture |
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New 914 rear wheel bearing, No to very little grease from manufacture |
Luke M |
Apr 10 2019, 12:05 PM
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#1
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Senior Member Group: Members Posts: 1,373 Joined: 8-February 05 From: WNY Member No.: 3,574 Region Association: North East States |
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 |
Apr 12 2019, 06:35 PM
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#2
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914 Guru Group: Members Posts: 5,875 Joined: 25-August 18 From: Woods of N. Idaho Member No.: 22,428 Region Association: Galt's Gulch |
(IMG:style_emoticons/default/happy11.gif)
Not done yet. Bearing pre-load, or clamp load if you will, is not so simple either. When you torque a fastener (I'll call it a joint) what you are doing is stretching the fastener like a spring. Let's call that force - clamp load. Clamp load is interdependent on torque. The problem is that torque varies greatly depending on the nut tolerances, the plating type (black oxide vs. Zinc for example), whether the fastener is lubricated, etc. The joint clamp load needed is usually determined by lab testing and/or vehicle durability testing and/or past design history of success. However the OEM establishes this with new fasteners with what ever lube would be on them from the fastener manufacturing process. So in the end, they are trying to achieve a certain clamp load is roughly equivalent to a certain torque using the fasteners as they would be in the factory new condition. Now, let's go to two extreme cases: 1) A heavily corroded fastener. I think we've all been there. It takes a lot of torque just to run the fastener down. That torque although high, isn't converted to clamp load. It's lost internal to the fastener as friction. Worst case, the bearing gets very little actual pre-load. That will lead to short bearing life. 2) Now put grease or maybe anti-seize on the threads of a new fastener that is maybe a bit on the loose side of manufacturing tolerance or maybe a used nut that is loose from having been on & off a dozen times (like a 50 year old 914 Hub nut?) Fastener now goes on with very little torque to turn (not much friction). Now when the torque spec is applied more of the torque is turned into effective clamp load. Clamp load is much higher, therefore bearing pre-load is higher. That will lead to shortened bearing life. Case #2 is why many new cars have hub nuts that are stamped - DO NOT REUSE. They are often have what is called prevailing torque fasteners (self locking). Lack of a castle nut and cotter pin is a clue that is probably is torque prevailing and single use only. Once they are used once, they will have lost their initial tolerances and "bite" on the threads. They will go on easier the next time, establish more clamp load, and will not effectively serve the locking function. How many times do these fasteners get reused? More often than you would want to know because a Tech may not know or may not care and just want to get the job off his hoist. Anyway . . . moral of the story is a bearing's life (or lack of it) isn't easily written off as not enough grease as many would have you believe. Sorry for the dissertation. (IMG:style_emoticons/default/sad.gif) |
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