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Mystery rear whine, I suspect the diff, but at a loss on diagnosing further

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Mystery rear whine, I suspect the diff, but at a loss on diagnosing further

 
Old 02-25-2019, 08:24 AM
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Question Mystery rear whine, I suspect the diff, but at a loss on diagnosing further

Background: recently acquired stock '08 with 33k miles.

Hoping to get some opinions before I take a gamble on a used diff, or spend a bunch on a built diff. Been thinking about ignoring the noise until something actually happens, but my brain ain't wired that way...

Symptoms:

A whine from the rear, most apparent between 40-55 mph, peaks in loudness at 45mph (to my ears anyway) - it's considerably louder than what I'd consider to be normal diff whine (which I can hear in this car, with a bit of effort, at other speeds). It's only present under light load (let's say 10% throttle), and disappears if the accelerator is released, or the clutch pedal is pushed in. Whine doesn't get louder with speed and ends up either fading away or getting drowned out above 60-65 mph; also, increasing throttle seems to fade the whine away as well (although things generally get louder, so it may be getting obfuscated). No grinding, rumbling, roaring, ticking, clunking, or vibrations present that I've been able to detect. Edit to add: Whine is easily heard in 4th, 5th, and 6th gears, I believe it's present in 2nd and 3rd too, but difficult to hear over the correspondingly louder mechanical symphony.

I did change the diff oil upon purchase, and it looked pretty old (dark and thick), drain plug had the typical dark paste, but no chunks or flakes; currently it's filled with M1 75w140. I've been under the car a few times and everything looks really good (as it should with this low mileage). I did also do the axle-nut 'tsb', and have tried a different set of rear tires - neither affected the noise.

I'm trying to figure out if this is near-term, medium-term, or long-term fatal to the diff, what it might actually be, and whether taking a flyer on a FB/Ebay diff is worthwhile.

Thanks.
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Old 02-25-2019, 10:47 AM
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I'm not sure if this just might be normal. I can hear a high pitched whine as well when i accelerate or let off the gas at certain speeds. Sometimes its loud enough that i can hear it over my aftermarket exhaust. I had my car looked at by Blacktrax (super reputable s2000 shop) and they didnt mention anything wrong with the car related to that. Part of me thinks its normal due to little to no sound dampening in this car, it being a roadster, and because racecar.

However please take my opinon with a boulder of salt as i'm not a mechanic and i dont know enough about this platform to know whats normal and what isnt...yet.
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Old 02-25-2019, 12:00 PM
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Originally Posted by xxyion View Post
However please take my opinon with a boulder of salt as i'm not a mechanic and i dont know enough about this platform to know whats normal and what isnt...yet.
Well, I've been out of the game for a few years, but I did own my first one for a decade... This sounds like more than a normal whine.

95% sure it's from the diff, but haven't definitively ruled out something else (although I can't think of what else it could be).
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Old 02-25-2019, 12:13 PM
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Doesn't sound normal to me. Its either the diff or the trans or possible CV in main driveshaft. Wheel bearing maybe. These are not easy sounds to chase and diagnose. You almost have to wait for something to fail before it becomes obvious. I'm chasing a interment sound myself, coming from the pass rear, which I think is a caliper sticking/dragging. Try and depict if the sound is centered or off to one side, that should help narrow down what it could not be.
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Old 02-25-2019, 12:41 PM
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Originally Posted by s2000Junky View Post
Doesn't sound normal to me. Its either the diff or the trans or possible CV in main driveshaft. Wheel bearing maybe. These are not easy sounds to chase and diagnose. You almost have to wait for something to fail before it becomes obvious. I'm chasing a interment sound myself, coming from the pass rear, which I think is a caliper sticking/dragging. Try and depict if the sound is centered or off to one side, that should help narrow down what it could not be.
Yeah, I've been trying to track it down definitively with limited success thus far. It does - to my ear - sound a bit biased toward the passenger side, but I think that's largely due to me sitting on the other. My initial inclination is to rule out transmission, as it very much sounds like it's behind the driver (if forced to guess, I pinpoint the noise as being from somewhere between the seats and trunk).

Speaking of brakes, I did try a couple of clicks on the handbrake while at full whine and that didn't change anything, so I don't believe brakes to be involved in my case. Wheel bearings ... I suspect that wouldn't be dependent on throttle/load, my expectation would be that in that case the noise would be constant regardless of throttle, but maybe that's bad thinking. Also, when my 1st S had rear wheel bearings go kaboom, I don't remember ever hearing a whine - more of a roaring/rumbling that got louder until it was a crunching/grinding (I figured I may as well get all the way home - which it turns out you can do even with multiple bearing balls being in pieces).

I hadn't considered propshaft CV as a possible source ... anyone know how much rotational play I should have in the propshaft? How much axial play? Can't think of any other diagnostics in that area, but welcome any suggestions...
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Old 02-25-2019, 02:56 PM
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Originally Posted by vjarnot View Post
Yeah, I've been trying to track it down definitively with limited success thus far. It does - to my ear - sound a bit biased toward the passenger side, but I think that's largely due to me sitting on the other. My initial inclination is to rule out transmission, as it very much sounds like it's behind the driver (if forced to guess, I pinpoint the noise as being from somewhere between the seats and trunk).

Speaking of brakes, I did try a couple of clicks on the handbrake while at full whine and that didn't change anything, so I don't believe brakes to be involved in my case. Wheel bearings ... I suspect that wouldn't be dependent on throttle/load, my expectation would be that in that case the noise would be constant regardless of throttle, but maybe that's bad thinking. Also, when my 1st S had rear wheel bearings go kaboom, I don't remember ever hearing a whine - more of a roaring/rumbling that got louder until it was a crunching/grinding (I figured I may as well get all the way home - which it turns out you can do even with multiple bearing balls being in pieces).

I hadn't considered propshaft CV as a possible source ... anyone know how much rotational play I should have in the propshaft? How much axial play? Can't think of any other diagnostics in that area, but welcome any suggestions...
Your leading me to the diff based on what im hearing so far. One thing you might consider is consulting with Puddydad, as he can give you some more in depth likely scenarios with what you are hearing inside the diff and some cost associated with those repairs if you decide to send to him for inspection and repair. The alternative is you bite the bullet and pick up a used diff and swap it in and hope that was it. So far im about 75% on the diff being the most likely issue.
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Old 02-26-2019, 07:34 AM
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Originally Posted by s2000Junky View Post
Your leading me to the diff based on what im hearing so far. One thing you might consider is consulting with Puddydad, as he can give you some more in depth likely scenarios with what you are hearing inside the diff and some cost associated with those repairs if you decide to send to him for inspection and repair. The alternative is you bite the bullet and pick up a used diff and swap it in and hope that was it. So far im about 75% on the diff being the most likely issue.
Appreciate the replies. Yeah, I'm like 95% on it being the diff, but am grasping at straws hoping it ain't Actually, I'm over 95% - I did end up reaching out to Puddydad and his initial impression is that it's probably the diff. I suspect this car spent a bit of time in the hands of a red-light drag champ .
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Old 02-26-2019, 01:51 PM
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Mystery ebay diff inbound. If nothing else, I'll have a spare to send PuddyMod's way.
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Old 02-26-2019, 01:53 PM
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Originally Posted by vjarnot View Post
Mystery ebay diff inbound. If nothing else, I'll have a spare to send PuddyMod's way.
update the thread when you get the diff installed or have puddydad crack open and confirm the issue.
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Old 02-26-2019, 02:33 PM
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I know you've already ordered, but any chance it could be the diff mounts? Not sure if it would cause the same issue
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