mountainred Posted January 31, 2006 Share Posted January 31, 2006 the file technique is something us old welders would do to help select a rod. A more accurate test would be a rockwell guage. We have to be sure that the shaft is harder than the clutch disc. Also if the shaft from bmw is the right alloy, it could be hardened. If hardening is not considered as part of the fix, I would be willing to bet that it will happen again. I did look at the shaft and my machinest friend at work said it would take him about a day to make because of the splines and a "one of" set up.At a local machine shop, that would be big bucks and you would still have to harden it after it is made at another cost. Link to comment
Kitsap Posted January 31, 2006 Share Posted January 31, 2006 How about this. Part of my job involves analysis of metals of various suppliers from all over the world for aircraft use. A failure in the fleet or factory gets the supplier's attention but metalurgical evidence is the clincher. If some of our members out there have failed spline sections they can hack off and send the samples to me I'll run them through the lab for granular analysis and makeup. It would be good to have a sample of "good" sections also but how many of you want to hack apart... PM me if so inclined and I'll get my contacts ready. Link to comment
SWB Posted January 31, 2006 Author Share Posted January 31, 2006 How about this. Part of my job involves analysis of metals of various suppliers from all over the world for aircraft use. A failure in the fleet or factory gets the supplier's attention but metalurgical evidence is the clincher. If some of our members out there have failed spline sections they can hack off and send the samples to me I'll run them through the lab for granular analysis and makeup. It would be good to have a sample of "good" sections also but how many of you want to hack apart... PM me if so inclined and I'll get my contacts ready. Nice offer. Recommend that you post it in a separate thread (maybe titled: "Have your splines failed, and do you still have the parts?"). This would certainly be helpful. But it'd really require BMW's engineering specs' and someone who knows how hard a shaft and splines should be, i.e. a mechanical or automotive engineer, to make sense of your data. But if you had the opportunity to check a half dozen (and the time), it'd paint a better picture than we have now, and give the guys stuck with this problem something to take to BMW. The more facts we put on the table (i.e. internet), the tougher it'd be for BMW to stonewall owners. <sidebar> The internet sure makes the world a more interesting place. Ten years ago, only a government dictated recall could cause a manufacturer to move. With the combined resources of the owners on this forum, we might just come up with a cause of failure, whether BMW wants to know about it or not. </end sidebar> Link to comment
nrp Posted January 31, 2006 Share Posted January 31, 2006 As an engineer with driveline material experience, I'd guess SAE 8620 carburized and case hardened to Rc 58 or so. Or it could be SAE 6150 and nearly Rc58. Or it could be SAE 4150 or similar. The range of alloys & necessary heat treats isn't that large for a seriously stressed shaft/spline application, although BMW would probably use a German alloy spec which would be similar to these. My guess is that the failed samples won't be soft, but that is only my speculation. That would have been too easy for the mnanufacturer to have fixed. Besides, harder stuff grinds easier. Several have said the clutch disk internal spline should be softer. Why? Several others have talked about rust etc being present. That is probably the result of fretting stress corrosion. The problem isn't the presence of an electrolyte - it is the continuous working (fretting) of the joint. I still have my runout measurement scheme only in a Word document. Sorry to be so computer illiterate. Link to comment
russell_bynum Posted January 31, 2006 Share Posted January 31, 2006 Several have said the clutch disk internal spline should be softer. Why? The thought is that the (expensive) shaft survives and the (relatively cheap) clutch internal splines fail. Link to comment
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