Trans/Front Diff Whine

[jamesturbo22]

Hey all, after much research among this forum and other places, I have not been able to find much related to the following problem noise I have, any help here would be appreciated.

I drive a 2011 S4, DSG transmission, sport rear differential, 160,000 kms. A while back I started to notice a faint hum/whine from the transmission, but it was barely noticeable. Recently, the noise has become much more noticeable, to the point of being able to hear it over a normal (quieter) music level. Its very similar to the whine of transport truck tires on the highway when you drive past them. Ive also noted that it only makes the whine when the car is being accelerated, slowly or fast, but disappears when you let off the throttle. The pitch of the whine increases with speed up to 100 kmh (60 mph) and then tapers off from there. Wheel bearings and tires are out of question, as well as rear differential.
From what I understand, there is a front differential as part of the transmission, located on the RH side, which powers the front half-shafts on both sides. Anyone ever see these fail? Does it share oil with the DSG section of the trans, or the center diff/gear section of the trans?
I regularly change oil well before intervals, but have been unaware of the gear oil section of the transmission, ive only ever changed the DSG oil and filters.

Any questions, ideas and inputs are appreciated!

[JRYtheS4]

Hey all, after much research among this forum and other places, I have not been able to find much related to the following problem noise I have, any help here would be appreciated.

I drive a 2011 S4, DSG transmission, sport rear differential, 160,000 kms. A while back I started to notice a faint hum/whine from the transmission, but it was barely noticeable. Recently, the noise has become much more noticeable, to the point of being able to hear it over a normal (quieter) music level. Its very similar to the whine of transport truck tires on the highway when you drive past them. Ive also noted that it only makes the whine when the car is being accelerated, slowly or fast, but disappears when you let off the throttle. The pitch of the whine increases with speed up to 100 kmh (60 mph) and then tapers off from there. Wheel bearings and tires are out of question, as well as rear differential.
From what I understand, there is a front differential as part of the transmission, located on the RH side, which powers the front half-shafts on both sides. Anyone ever see these fail? Does it share oil with the DSG section of the trans, or the center diff/gear section of the trans?
I regularly change oil well before intervals, but have been unaware of the gear oil section of the transmission, ive only ever changed the DSG oil and filters.

Any questions, ideas and inputs are appreciated!

Might seem dumb, but check your tire wear and pressure. I've seen on other cars that a pressure or treadwear mismatch can make a diff unhappy.

Sent from my SM-G991U1 using Audizine Forum mobile app

[jamesturbo22]

Ok i will check pressures, however it seems odd that the whine is only audible with acceleration

[JRYtheS4]

Ok i will check pressures, however it seems odd that the whine is only audible with acceleration

Yeah it's just the "turn it off then back on" type response I have for differential and trans noises. On my manual car if you run like 5 psi difference side to side it feels harder to get into gear. Audi also has a spec for treadwear "evenness" from wheel to wheel. I forget the figures exactly but if the tires are wearing differently and they aren't rotated it can cause issues with the AWD system in extreme cases.

Sent from my SM-G991U1 using Audizine Forum mobile app

[jamesturbo22]

Yeah it's just the "turn it off then back on" type response I have for differential and trans noises. On my manual car if you run like 5 psi difference side to side it feels harder to get into gear. Audi also has a spec for treadwear "evenness" from wheel to wheel. I forget the figures exactly but if the tires are wearing differently and they aren't rotated it can cause issues with the AWD system in extreme cases.

Sent from my SM-G991U1 using Audizine Forum mobile app

Ah i see, yes that’s understandable. Its always good to start with basic diagnostics, since its easy to assume the worst case scenario. I will definitely take your advice into account, thanks for your time!

[jamesturbo22]

PROBLEM SOLVED: So I decided to go ahead and check the center diff/main gearbox oil level. Nothing ran out of the fill plug, so I added 2 L of gear oil, and as far as I can see with my phone camera in the hole, im roughly halfway filled, (2.5 L out of the 4.5L capacity.) This would explain the diff whine, as im assuming that there was enough oil to splash lube the gears and synchros, but not enough to reach the front differential. I will get it filled up completely and test run to see if the whine lessens or disappears. All in all, check your levels folks, and hopefully this helps someone else.

[Nillious]

Gear whine that appears over time or suddenly means that something has moved or clearances have changed. Especially how you mention only on acceleration you hear it. I’m afraid maybe the damage has been done. Hopefully that is not the case. You need to figure out where it went to prevent further damage in the future. What kind of oil did you add to it?

[jamesturbo22]

Gear whine that appears over time or suddenly means that something has moved or clearances have changed. Especially how you mention only on acceleration you hear it. I’m afraid maybe the damage has been done. Hopefully that is not the case. You need to figure out where it went to prevent further damage in the future. What kind of oil did you add to it?

Yes I'm afraid that the damage has been done, however, the transmission still shifts ok. I think its more a matter of limited lifespan at this point. I have added the Royal Purple 75W-90, GL-4 rated oil to it, and I will probably run with that for 20 kms or so and then drain all of it and fill with the OEM Audi oil to be 100%.

[doughboy17]

Yes I'm afraid that the damage has been done, however, the transmission still shifts ok. I think its more a matter of limited lifespan at this point. I have added the Royal Purple 75W-90, GL-4 rated oil to it, and I will probably run with that for 20 kms or so and then drain all of it and fill with the OEM Audi oil to be 100%.

I am interested to hear how your experience transpires. This winter I began to hear a similar noise and initially thought it was another wheel bearing but began to question that diagnosis when the behavior was similar to yours (although maybe not as loud). My Indy shop cannot look at my car until Mon.

[jamesturbo22]

I am interested to hear how your experience transpires. This winter I began to hear a similar noise and initially thought it was another wheel bearing but began to question that diagnosis when the behavior was similar to yours (although maybe not as loud). My Indy shop cannot look at my car until Mon.

Ok yeah, so i filled up the gearbox, and took it for a good long run on the highway. The whine is still there, but dosent seem to be getting worse. I even ended up racing a new Nissan Z, and got up to 200 kmh, nothing has blown apart in the diff or gearbox yet. The synchros all seem ok, everything shifts like butter. Im suspecting the diff bearing got hot previously, and now the only remedy would be to take that apart and see if i can find an overheated bearing.

Sent from my SM-A426U1 using Audizine Forum mobile app

[doughboy17]

Ok yeah, so i filled up the gearbox, and took it for a good long run on the highway. The whine is still there, but dosent seem to be getting worse. I even ended up racing a new Nissan Z, and got up to 200 kmh, nothing has blown apart in the diff or gearbox yet. The synchros all seem ok, everything shifts like butter. Im suspecting the diff bearing got hot previously, and now the only remedy would be to take that apart and see if i can find an overheated bearing.

Sent from my SM-A426U1 using Audizine Forum mobile app

Thanks for the update! Did you figure out whether the front differential, located on the RH side, shared oil with the DSG section of the trans or the center diff/gear section of the trans? Can you please verify for me that you filled the center diff. with your specified gear oil and not with Dual-Clutch Transmission fluid? Was the fill hole/ location different than where the transmission/ dual-clutch fluid is filled? Thanks!!

[jamesturbo22]

Thanks for the update! Did you figure out whether the front differential, located on the RH side, shared oil with the DSG section of the trans or the center diff/gear section of the trans? Can you please verify for me that you filled the center diff. with your specified gear oil and not with Dual-Clutch Transmission fluid? Was the fill hole/ location different than where the transmission/ dual-clutch fluid is filled? Thanks!!

No problem! Ok, so the answer is no, the center diff does not share oil with the DSG section of the transmission. The front RH differential however, does share oil with the center diff.
- Centre diff/front RH diff oil - 75w-90 GL-4 spec, do not use GL-5 spec, it reacts with brass in synchros.
- There are multiple threads on this forum that explain how to service the DSG portion of the transmission. The fill and drain holes are completely separate from the center differential. The center diff fill and drain holes are directly in-line with the rear transmission mount, so farther back than the DSG ones. A little hard to get to, but accessible enough.
Hopefully this helps!

[doughboy17]

No problem! Ok, so the answer is no, the center diff does not share oil with the DSG section of the transmission. The front RH differential however, does share oil with the center diff.
- Centre diff/front RH diff oil - 75w-90 GL-4 spec, do not use GL-5 spec, it reacts with brass in synchros.
- There are multiple threads on this forum that explain how to service the DSG portion of the transmission. The fill and drain holes are completely separate from the center differential. The center diff fill and drain holes are directly in-line with the rear transmission mount, so farther back than the DSG ones. A little hard to get to, but accessible enough.
Hopefully this helps!

Thanks much for the explanation and detailed info.!!