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Old 25th April 2007, 23:34   #1
Z8 HM
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Dinan Differential Update

I had my 3.91 Dinan differential installed 6 weeks ago by Dinan at their Mountain View shop. From day one, it whined. After two weeks, I complained and they asked me to bring in the car immediately for a day. At the same time as setting up my appointment, they ordered me a new differential and let me know that it would not be in in time for my appointment, but they wanted to check my differential anyway.

After a half day, they returned the car and let me know that I did not have any cover interference problems, and so therefore, that was not the source of the noise. (I think they wanted to check this quickly, so to minimize damage if there were filings in the oil). They asked if I wanted my factory diff back in or if I wanted to stay with the whining diff until the new one arrived. I elected to stay with the 3.91.

Yesterday (3 weeks later), I had the new differential installed, and all noise is gone. The difference is amazing. I am not a rear-end expert, but the following was explained to me. My new differential has an all new gear design. Apparently there is a real art to gear design. There are direct tradeoffs between noise and parasitic loss in the differential. If the gear faces are closer to perpendicular (straight cut), there is less loss, but potential for lots of whining. As the angle becomes less, the gears get quieter, but parasitic losses go up. The trick is to find the optimal point. I can attest that this new gear set is dramatically quieter.

I have been thoroughly impressed with Dinan's service and professionalism throughout this entire process. A class outfit.

Z8 HM

PS They've said no break-in, other than coming back after 1,000 miles.
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Old 25th April 2007, 23:39   #2
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Quote:
Originally Posted by Z8 HM View Post
I had my 3.91 Dinan differential installed 6 weeks ago by Dinan at their Mountain View shop. From day one, it whined. After two weeks, I complained and they asked me to bring in the car immediately for a day. At the same time as setting up my appointment, they ordered me a new differential and let me know that it would not be in in time for my appointment, but they wanted to check my differential anyway.

After a half day, they returned the car and let me know that I did not have any cover interference problems, and so therefore, that was not the source of the noise. (I think they wanted to check this quickly, so to minimize damage if there were filings in the oil). They asked if I wanted my factory diff back in or if I wanted to stay with the whining diff until the new one arrived. I elected to stay with the 3.91.

Yesterday (3 weeks later), I had the new differential installed, and all noise is gone. The difference is amazing. I am not a rear-end expert, but the following was explained to me. My new differential has an all new gear design. Apparently there is a real art to gear design. There are direct tradeoffs between noise and parasitic loss in the differential. If the gear faces are closer to perpendicular (straight cut), there is less loss, but potential for lots of whining. As the angle becomes less, the gears get quieter, but parasitic losses go up. The trick is to find the optimal point. I can attest that this new gear set is dramatically quieter.

I have been thoroughly impressed with Dinan's service and professionalism throughout this entire process. A class outfit.

Z8 HM

PS They've said no break-in, other than coming back after 1,000 miles.

GREAT NEWS! I'm due for replacement next week.......and I agree......Dinan has been first class throughout this....

Thanks for sharing!
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Old 26th April 2007, 00:43   #3
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Quote:
Originally Posted by Z8 HM View Post
...
Yesterday (3 weeks later), I had the new differential installed, and all noise is gone.
...
I can attest that this new gear set is dramatically quieter.
...
Did Dinan say:

Whine is totally eliminated?

And any possibility of hearing any whine at all?
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Old 26th April 2007, 01:02   #4
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Good to hear your positive outcome. I talked to my sales guy there today and it looks like they're on back order so I'll wait.
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Old 26th April 2007, 03:11   #5
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That doesn't make sense. How could I have one of the first diff's and it not whine? Is there that much variabilty in the gear angle/set-up from diff to diff so that some of them whine and some don't? Is there now a new "quality control" regarding the angle to optimize performance and minimize whine. I'm happy they worked it out though.
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Old 26th April 2007, 04:02   #6
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Quote:
Originally Posted by 905RMP32V1x View Post
That doesn't make sense. How could I have one of the first diff's and it not whine? Is there that much variabilty in the gear angle/set-up from diff to diff so that some of them whine and some don't? Is there now a new "quality control" regarding the angle to optimize performance and minimize whine. I'm happy they worked it out though.
This is from a post of mine on the same subject:

We are still a fews days out for the replacement of the differential, but my SA, who is clearly an M Fan-atic.......offered HIS opinion on what's going on with these things.....he offered his opinion after a lot of back-and-forth with Dinan. That said, and for what its worth, he thinks it has to do with something called "backlash" being set too tight....causing the gears to whine as they warm up and pressure between them increases. I do recall that the whirring was not there when the car was cold...

So if (and yes, its a BIG if) this is an assembly problem, it makes complete sense why one differential made right after another one will whine while the first one doesn't. While no one knows for sure at this point, this fits the symptoms: The only apparent difference between these things is how they are put together.....the gears, covers, and dealer installation practices all seem to have been eliminated as the cause.....the Human Factor of strict adherence to assembly specs seems to be the next potential suspect in line....

That said:

We are all car nuts to one degree on another, and we want to know everything about everything about everything, in detail, in triplicate.......but as a simple consumer, you can't ask for better service......no questions asked, a loaner for as long as it takes......frequent updates to keep me posted, etc....I won't go as far as to say its been enjoyable, but I have A LOT of awful stories about car dealers and service.



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Old 26th April 2007, 04:08   #7
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The Dinan diffs no longer have a whine, as there was a clearance modification done to the diff cover that was causing this whining noise. It is also very important that the dealer tightens the diff cover bolts in the correct order with the correct amount of torque, or this can also cause a gear whine. We are going to get a chance to drive ours next week on Tuesday with all the Dinan upgrades done.
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Old 26th April 2007, 04:31   #8
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Great!!!!

That's great News Z8 HM...I'm dropping my beast of in the morning to have my whining dinan diff replaced with the modified one. Thanks for sharing.
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Old 26th April 2007, 12:17   #9
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My car is going in in about an hour to have the dif installed. Crossing my fingers.
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Old 26th April 2007, 12:33   #10
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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.

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