Originally Posted by
kaneda
apparently it was the plates/washers under the bolts that seem to have been the issue , it almost looks like they were done up then backed off then done up again??
Did the washers get reused on after the 1st repair?
They could have yielded and compressed, reducing the installed preload, after the bolts were torqued up.
I'm looking at the pics on the ARP site on failure modes vs your sheared bolt pic and the Impact Shear (#3) seems to be the best fit. The following point in the article seems particularly relevant
Failures due to impact shear occur in bolts loaded in single shear, like flywheel and ring gear bolts. Usually the failed bolts were called upon to locate the device as well as to clamp it and, almost always, the bolts were insufficiently preloaded on installation. Fasteners are designed to clamp parts together, not to locate them. Location is the function of dowels.
The comment about the function of bolts echoes Carroll Smith's words on the subject.
The VW design for the ring gear / differential assembly seems to rely on precise assembly which is probably why they use rivets as they can accurately predict the installed preload on the rivets (which are also designed to be used primarily in shear rather than tension, unlike bolts). I'd be checking if the stretch of the bolts could be specified rather than the torque for the diff reassembly - at least it be easy to measure.
Last edited by kaanage; 21-12-2011 at 10:56 PM.
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