Differential noise - 74 Spider; 40k miles - Page 2 - Alfa Romeo Bulletin Board & Forums
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post #16 of 19 (permalink) Old 10-06-2017, 04:36 PM
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It occurs when you unload the drivetrain by cutting back on the gas or giving no gas and coasting. It does not happen during acceleration.

From a mechanical stand point what is going on inside the differential to cause the growling noise?


Hijack!! What causes a diff to whine under load,no noise coasting,just the opposite of Marks problem?
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post #17 of 19 (permalink) Old 10-06-2017, 04:46 PM
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Same exact list. Its a bit of 'mystery' on exact pinpoint causes for these whines, but they all relate to incorrect pinion-to-crown gear relationship. Only two adjustments are possible though -- pinion to crown depth (how far radially the pinion is located relative to crown wheel center) and pinion-to-crown wheel clearance (how much gap there is between the pinion hypoid gear and the crown wheel 'teeth'). Pinion yaw and attack angle are NOT adjustable at all (for me at least).

I tend to look at lash as the very first thing to see where it is, lash is absolutely needed but can not be excessive. CHapter ?17? of the service manual gives all the specs and test methods.

You could try swapping the diff oil to something else like mineral oil or other. The experts on this forum on this is Alfar7 (RJ) and little Italian (bud) for sure.

74 GTV with 10548's and Ingram pump
71 Spider 1750 BOMBER ; 1995 LS 78K tight fast car
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post #18 of 19 (permalink) Old 06-15-2019, 07:45 AM Thread Starter
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I'm resurrecting this post because I was finally able to get the car into the shop for this aliment. When they opened up the differential on the bench they found 0 pre load on the pinion nut. They were unable to find the correct setting but left it at 13 in. lb. After re-installing the rear axle and test driving the noise was still there and occurred under the same conditions previous to the tightening of the pinion nut. After discussion with the mechanic and some reading I'm thinking there are 3 options to pursue.

1. Have the shop change the thickness of the shims.
2. Replace the bearings, even though the mechanic said he does not think they are the culprit.
3. Replace the rear axle & differential.

Any input or advice is most welcome.

Also, do you think the tourque setting on the pinion nut should be greater than 13 in. lb.?


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post #19 of 19 (permalink) Old 06-15-2019, 07:50 AM
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Option 3!

Don`t try to rebuild a worn differential. Replace it in it`s entirety.

Richard Jemison
RJR Racing

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