Differential sound after rear end refresh

[_10speed]

Hey gang.

Just finished installing CMP solid subframe bushings, CMP solid differential bushings, replaced all the suspension bushings with new ball joints and sphericals. (autocross street mod car)

When I got the diff off the car, I noticed had a decent amount of output flange play on the drivers side. The car is a 2005 with the original differential. You could probably wobble the flange 3/8". Passenger side was solid, no movement. Also to note, no diff sounds out of the ordinary before this evolution. The car was previously on powerflex poly subframe bushings, and AKG 95A poly diff bushings. The diff was quite oily, and it was too difficult to know where the leaks were coming from.

Quite evident the diff was in less than good health at 140K miles, I decided to replace the diff seals, refresh the fluid and monitor, hoping to get one more season out of the diff before a rebuild.

I got the car on the road and immediately noticed a notable "whirrr" sound, or a sound like "zzzzzz". The sound is speed dependent. I have the sound when I clutch in. No noticeable leaks after only a few miles drive.

Repacked the drive shaft CV, and torqued everything by the Bentley.

Have a listen in the video and let me know what you think.

Thanks.

https://www.youtube.com/watch?v=yc-aer7GzXs

[Thoglan]

That's what happens when you have solid diff bushings. Diff whine, judging by the video.
The backlash on the driver side output shaft is normal I believe and 'by design'. IIRC there was a service bulletin by BMW saying specifically that the play in the left side output shaft is normal. Probably what causes the infamous m clunk. Not necessarily indicative of a knackered diff but at 140k miles its probably past its best before. The diffs in these are a bit meh imo. Clunky and not overly robust.

[SQ13]

Yeh that’s diff whine thanks to your solid diff mounts. Unless it’s a racecar, ditch those for rubber or maybe soft poly mounts. Soft poly mounts like the AKG 95A mounts will still introduce a faint whine, but it’ll be a lot more bearable than solid bois. Keep the solid subframe mounts tho…they aren’t the cause of this noise.

[EthanolTurbo]

That's why "upgraded" diff bushings suck. Go back to OEM. There's no point and your ears will thank you.

[_10speed]

The car is a track car, so I am cool with the NVH added by solid bushings.

The directness the solid diff bushings add to the drivetrain are a nice improvement!

What I am trying to determine if what I am hearing is the added NVH to be expected, or the sign of something wrong with the diff, axles, or driveshaft.

The diff whine in the video is easy to hear. That's not what I am trying to pin point as the issue. It kinda sounds like a hiss in the video. It gets louder based on speed. Its sounds like a metal on metal rotational sound, like if something was overtightened, or the sound a worn bearing would make.

On that note, the wheel bearings were done about 30K ago, and this sound didn't exist before this recent overhaul.

[Cubieman]

Check your dust shields.
When I had the whole rear-end dropped at times the dust shields were taking a bunch of weight and bent to where the inner portion was touching the rotors.

[_10speed]

It’s for sure not the dust shields. Cut them off!

[fattycharged]

That's definitely what mine sounds like

[AussieE46M3]

Hey gang.

Just finished installing CMP solid subframe bushings, CMP solid differential bushings, replaced all the suspension bushings with new ball joints and sphericals. (autocross street mod car)

When I got the diff off the car, I noticed had a decent amount of output flange play on the drivers side. The car is a 2005 with the original differential. You could probably wobble the flange 3/8". Passenger side was solid, no movement. Also to note, no diff sounds out of the ordinary before this evolution. The car was previously on powerflex poly subframe bushings, and AKG 95A poly diff bushings. The diff was quite oily, and it was too difficult to know where the leaks were coming from.

Quite evident the diff was in less than good health at 140K miles, I decided to replace the diff seals, refresh the fluid and monitor, hoping to get one more season out of the diff before a rebuild.

I got the car on the road and immediately noticed a notable "whirrr" sound, or a sound like "zzzzzz". The sound is speed dependent. I have the sound when I clutch in. No noticeable leaks after only a few miles drive.

Repacked the drive shaft CV, and torqued everything by the Bentley.

Have a listen in the video and let me know what you think.

Thanks.

https://www.youtube.com/watch?v=yc-aer7GzXs

Hey mate,

Based on the video that sounds like normal solid mounted diff noises. I've got the same solid diff & subframe bushings in a Non-M and it sounds identical (although a little quieter being a smaller diff with taller gearing). You may also hear the clutches when going around tight corners at low speeds.

If the diff noise ever becomes an issue, using stock diff bushings even with aluminium subframe mounts will transmit no diff whine (unless the diff is on its way out).

If anyone else finds themselves in this situation, I'd suggest stock over poly. Poly will still transmit diff noise and the front bush has only 3.3mm of dampening material around a stainless steel core so even hard poly's will flex similarly. E36 rear bushings can be used instead of replacing an entire diff cover if on a budget.

[sapote]

1. I noticed had a decent amount of output flange play on the drivers side.
2.The diff was quite oily, and it was too difficult to know where the leaks were coming from.

1. No driver nor passenger side, as it is country dependency. Just say left side or right side. Yours is a new version V2 with more plays on the left output flange as it is a shorter spline shaft; the early cars have V1 with the short right side flange and has more plays.
2. The excessive plays on the LH flange worn out the oil seal and it is the source of the leak and needs replacing, not the rear cover seal.

[_10speed]

Hey mate,

Based on the video that sounds like normal solid mounted diff noises. I've got the same solid diff & subframe bushings in a Non-M and it sounds identical (although a little quieter being a smaller diff with taller gearing). You may also hear the clutches when going around tight corners at low speeds.

If the diff noise ever becomes an issue, using stock diff bushings even with aluminium subframe mounts will transmit no diff whine (unless the diff is on its way out).

If anyone else finds themselves in this situation, I'd suggest stock over poly. Poly will still transmit diff noise and the front bush has only 3.3mm of dampening material around a stainless steel core so even hard poly's will flex similarly. E36 rear bushings can be used instead of replacing an entire diff cover if on a budget.

I appreciate the feedback! I am ok with the extra noise. It's my track car. So far, I really enjoy the extra response. Just really wanted to make sure I didn't mess something up in the process. Went for a longer drive tonight and no issues.

[_10speed]

1. No driver nor passenger side, as it is country dependency. Just say left side or right side. Yours is a new version V2 with more plays on the left output flange as it is a shorter spline shaft; the early cars have V1 with the short right side flange and has more plays.
2. The excessive plays on the LH flange worn out the oil seal and it is the source of the leak and needs replacing, not the rear cover seal.

Thanks for clarifying that. That is correct, LH side on a V2 diff. Replaced the oil seals and no leaks so far!

[_10speed]

Here is another video with better sound from a GoPro and a mic. No rear seat or sound damping.

https://www.youtube.com/watch?v=vFL70tDLKkk

[Obioban]

This is precisely why I don’t like noisy parts, even for track only cars— makes it way harder to diagnose any actual issues.

[bigjae46]

My car sounds like it’s broken. Rattles, whines, clunks, and vibrations. All normal when you strip the car down and have solid driveline mounts.

I just rebuilt two more diffs which were worn out. The play in the axle indicates excessive clearance in the clutch pack in the limited slip carrier.

I’m doing one now that was literally an open diff. Jacked up one rear wheel and it spun by hand. The limited slip carrier had a lot of play in the spider gears because the clutch discs were worn smooth. Worn so bad that the ring that goes between the spider gears and clutch pack was gouged by the carrier.


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