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Old 11-04-2019, 09:21 AM
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Loud whine when letting off throttle?

My C6 Corvette 90K miles, transmission is A4 / 4L60 I believe and this year is known to have a weak differential - but usually they do fine with automatics.

Pretty sure the car was fine a few weeks ago, I was driving it a bit hard going wide open throttle at times - but nothing abusive, suddenly it has developed a moderate or semi-loud "gear sounding" whine in the rear when you let off the throttle after coming off a moderate or hard acceleration - much louder when letting off throttle at higher speeds like 50-60mph. If I shift to neutral during the whine it mostly goes away (as your taking the load off the differential - although also taking the load off transmission, so who knows). The transmission holds power great and shifts perfect/smooth, so hoping its okay, but just not sure as it is mounted to the differential in the rear so I can't isolate the noise to one or other. There is no noise during acceleration or when your on the throttle - only when you let off.

The only other thing I did recently was have new tire sensors installed and tires balanced, balance is good as it was done twice; i tried rotating rears but it did not help noise. I think its probably a coincidence as I can't see how else the tire work could cause this, but I really didn't notice this issue before the work. I removed the tires myself, so the garage couldn't have messed up the car.

Does this sound like the automatic transmission or differential?

Could driving it a bit hard over the last few weeks have thrown the differential gear backlash out of alignment?

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Old 11-04-2019, 09:58 AM
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the trans should definitely make different noises when in different gears, you should be able to put the shifter in 2 or 3 and run it up to speed and see if the noise is the same. If the noise is the same it's likely in the diff.
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Old 11-04-2019, 12:04 PM
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Quote:
Originally Posted by lmsport View Post
the trans should definitely make different noises when in different gears, you should be able to put the shifter in 2 or 3 and run it up to speed and see if the noise is the same. If the noise is the same it's likely in the diff.
So I just drove it and tried this; you really have to get above 45 to hear a loud whine - so at that speed in 2nd gear the RPMs are covering some of the whine sound - its still there in second, but much louder in 3rd - but probably just because rpms are lower, I think at least.

Really does seem to be the differential, but I don't understand how this could happen out of nowhere, there was no gradual lead up to this - it was fairly quiet just a few weeks ago.
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Old 11-04-2019, 12:32 PM
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sudden gear whine is not normal for this or any diff, really, unless being pushed very hard.
that Getrag is tough, the cases and internal axles can break on some versions but the gears and bearings are not fail prone.
If you let it shift to 4th does it change the noise from 3rd?
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Old 11-04-2019, 12:54 PM
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turn the radio up
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Old 11-04-2019, 02:16 PM
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Check the pinion nut to see if it is still tight. If it's loose then torque it to about 125-150 foot pounds and see if the noise goes away. It's common for the pinion nut to back off and usually only makes noise under deceleration.
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Old 11-04-2019, 05:36 PM
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Quote:
Originally Posted by big gear head View Post
Check the pinion nut to see if it is still tight. If it's loose then torque it to about 125-150 foot pounds and see if the noise goes away. It's common for the pinion nut to back off and usually only makes noise under deceleration.
I believe its covered by the transmission bellhousing, but will definitely double check that if end up pulling it.
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Old 11-04-2019, 05:46 PM
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Quote:
Originally Posted by lmsport View Post
sudden gear whine is not normal for this or any diff, really, unless being pushed very hard.
that Getrag is tough, the cases and internal axles can break on some versions but the gears and bearings are not fail prone.
If you let it shift to 4th does it change the noise from 3rd?
I haven't been near a highway lately, but had it up over 70 a few brief seconds earlier and the whine seemed to be even louder, I think the faster you go the worse it gets. That may have been 3rd gear still though, I'll try to get it on a longer stretch tomorrow and listen more.

Yes thats my understanding is that its more prone to just grenade under a huge amount of stress like dropping the clutch on a manual car, but haven't heard that there is an issue with the gears/bearings themselves and most auto guys do just fine with this model getrag - so hoping its okay.
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Old 11-04-2019, 05:51 PM
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the pinion comes out the rear, take of the tin cover and you are looking right at it, the nut is about 3 inches in diameter and takes special pin drive socket, it should be staked to the pinion gear so if it moved it should be obvious. You might be able to get the pinion and support out the back, but I'm not sure it will and may depend on gear ratio, I haven't tried that before in the car but I do it on the bench.
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Old 11-04-2019, 06:21 PM
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I didn't pay attention to which series of Vette you have, so this might not be a problem with this car.
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Old 11-17-2019, 06:12 PM
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Quote:
Originally Posted by big gear head View Post
Check the pinion nut to see if it is still tight. If it's loose then torque it to about 125-150 foot pounds and see if the noise goes away. It's common for the pinion nut to back off and usually only makes noise under deceleration.
Thanks, the pinion nut looks okay, I am not able to check the torque on it - but couldn't see any visible looseness. The pinion nut lined up flush with back of pinion too - so it appeared to have not backed off at all if thats how its designed.
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Old 11-17-2019, 06:19 PM
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Quote:
Originally Posted by lmsport View Post
the pinion comes out the rear, take of the tin cover and you are looking right at it, the nut is about 3 inches in diameter and takes special pin drive socket, it should be staked to the pinion gear so if it moved it should be obvious. You might be able to get the pinion and support out the back, but I'm not sure it will and may depend on gear ratio, I haven't tried that before in the car but I do it on the bench.
Lmsport, I pulled the Pinion assembly out with the Getrag on the car today. Did not loosen pinion nut to do this - just pulled the whole assembly. To my amazement and frustration the Pinion and Ring gear are perfect - zero damage. The Pinion assembly with the nut and bearing did not have any vertical play - the bearing does allow forward and backward play when mounted upright, assume this is normal.

I am just lost at this point!
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Old 11-17-2019, 06:21 PM
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Could anyone comment on how I can know if this whine is my 4L60-E transmission or if it's really the differential?

Right now it makes the whine in all transmission gears - but only when you let off the throttle; it gets much much louder the faster you go - 70 is very loud, noise starts around 30mph and up.

If I put the transmission in neutral the noise goes away - but I just don't know if that points to the tranny as your taking the load off the differential by doing that.

The one thing I did notice after pulling the pinion assembly out - is that the transmission shaft in the differential does have a little play if I shake it with force - it moves at least 1/2" in any direction with force applied - not sure if this is normal or not?
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Old 11-17-2019, 06:31 PM
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in other rear ends the only movement that there should be in the pinion is rotation. If there is any in and out or up and down movement then something is wrong. I don't have any experience with this differential, so I'm not going to try to say for sure how this one should be.
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Old 11-17-2019, 06:32 PM
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I am not sure what you mean by "forward and back play", do you mean the backlash from the pinion gear to the ring gear?
The pinion assembly with the aluminum housing, and the two bearings should have no perceptible play, when rotating the gear the bearings should feel perfectly smooth.
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