Join Date: Mar 2004
Location: Atherton, CA
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Sounds like there may be mutiple problems out there. I am sure that I had no cover clearance problem. 3 weeks ago, when I brought the car in, that was the first thing they checked. Also, my whine was only on deceleration or moderate load cruise. It was not present with acceleration. I can't imagine that a noise as loud as I heard, consistently, was due to interference with a differential cover. If all it was was the cover, they would have fixed it 3 weeks ago and saved themselves the trouble of ordering and install a whole new differential.
Then there is the backlash/adjustment vs gear design question. I clearly had to wait for some new part or procedure to be put in place before this "new" differential was available. The head of Dinan Mountain View specifically told me that I got a differential with a new gear design. It may be possible that an "old" gear design could be quiet with the right backlash adjustment, but I am suspicious that if that were the case, they would have pulled my differential and reworked it to solve the whine. Instead, they waited until they had a new design.
The only explaination I can come up with for the mix of whining diffs and non-whining diffs out there so far is that perhaps there are multiple manufacturers of the gears used ( I think an earlier post referred to BMW gears and a new design both being used). My original differential was certainly a later install (done in March), so perhaps Dinan had run out of the original gear sets and was using a new supplier?
In my amateur sleuthing on gear whine and differentials, I also found papers that indicated that noise (and parasitic loss) can be caused by the type of surface that the gears have. You can specify micro-polished surfacing (which is quiet but expensive) for instance. This leads me to believe that if Dinan's spec to their suppliers was loose on tolerances for surfacing, they might have gotten some variabilty there, and that was the source of noise.
Only Dinan really knows what is going on, as they clearly will have the serial number of each differential installed, the supplier used for the components, and the assembly procedure used to put the differential together. They can take all that data and correlate it with "whining".
I don't mean this to be critical of Dinan at all. As a business, they probably want to avoid a mass recall. So, they have adopted a policy that says if the customer is unhappy, fix it asap. Otherwise, leave it alone. I think that's smart business.