Do I NEED a new diff?

[BrutalS65]

Right fellas, I’ve had my E92 M3 DCT for about 3 weeks. Today my diff was making noises at slow, sharp right turns so I just had its oil changed. The specialist I took it to completed the job but told me the bolts were rusted and they had trouble taking them off. Soon enough, oil was changed and they told me they waved a magnet over the black oil and it was pretty bad.

When collecting my car they told me, ‘your diff hasn’t been serviced ever and it’s not going to last long with the wear and tear going forward’. Should I be alarmed? I’ve been looking at diffs and they’re not expensive, do I just go ahead and get my diff changed?

Any advice is appreciated

[nrubenstein]

Drive it until it actually fails. A little noise in turns is normal for these diffs - BMW updated the fluid to make that happen less.

[Redd]

What's your mileage? BMW claims the diff oil is 'lifetime'. Obviously fresh diff oil is good but don't be too worried if yours has not been serviced for a while.

As mentioned above, diff grinding at low speed full-lock turns is normal. If it bothers you try adding some friction modifier into the diff. Just know that adding FM makes the diff lock slower/less.

[tbuck]

I agree with the drive it till it fails. There are any number of noises that are totally normal for these car with any miles on them. And there are certainly thing to go preventative on, rod bearings of course, but a diff does not number among them (unless you track the car, then maybe). Worse case here it the clutches begin to fail and then you can start planning to get a rebuild or a swap for something better. Welcome to the club and enjoy!

[DukeofAlexandria]

Originally Posted by nrubenstein

Drive it until it actually fails. A little noise in turns is normal for these diffs - BMW updated the fluid to make that happen less.

This.^

Also, you gave us zero info on your car that matters. Year, mileage, history of racing/dogging the car?

-Duke

[smyles]

Originally Posted by Redd

What's your mileage? BMW claims the diff oil is 'lifetime'....

I believe BMW prescribes " at every 3rd scheduled engine oil service: change the rear axle differential fluid."

[ChiTownM]

Also, when changing it there is a fluid with booster for older cars, I just had it changed.

Lifetime is for DCT fluid…YMMV.

[RocketyMan]

Originally Posted by Redd

What's your mileage? BMW claims the diff oil is 'lifetime'. Obviously fresh diff oil is good but don't be too worried if yours has not been serviced for a while.

As mentioned above, diff grinding at low speed full-lock turns is normal. If it bothers you try adding some friction modifier into the diff. Just know that adding FM makes the diff lock slower/less.

Unfortunately, there is no such thing as "lifetime oil fill." All this translates into is lifetime of the warranty period.

Servicing the diff is even more important when EITHER of the seals are compromised in the diff, thus, lowering the overall fluid level. Namely, the front pinion seal is a pretty weak one and fails regularly--by means of slow drip/seeping. Overtime, this will compromise your diff, and the misnomer of "lifetime fill" is not an excuse to neglect components like the rear diff, ergo not checking the fluid level at the very least/minimum.

FCP has an "updated" pinion seal that actually seals better than the original OE design.
https://www.fcpeuro.com/products/bmw...co-33121213949

There's also a nice video of the seal replacement, if yours is indeed leaking/seeping.

P.S. The e46 M3 rear diff seal is similar to E9X.

[Redd]

Originally Posted by smyles

I believe BMW prescribes " at every 3rd scheduled engine oil service: change the rear axle differential fluid."

Ah my bad. Cos the mechs here never change the rear diff fluid either. I do all my fluids at 30k kms, diff, DCT, everything.

[BP709]

Originally Posted by BrutalS65

Right fellas, I’ve had my E92 M3 DCT for about 3 weeks. Today my diff was making noises at slow, sharp right turns so I just had its oil changed. The specialist I took it to completed the job but told me the bolts were rusted and they had trouble taking them off. Soon enough, oil was changed and they told me they waved a magnet over the black oil and it was pretty bad.

When collecting my car they told me, ‘your diff hasn’t been serviced ever and it’s not going to last long with the wear and tear going forward’. Should I be alarmed? I’ve been looking at diffs and they’re not expensive, do I just go ahead and get my diff changed?

Any advice is appreciated

What fluid did you use? There is a bmw service information bulletin that addresses the exact noise you’ve experienced. Drain and refill the diff with XJ w/FM booster and then go drive the car slow tight circles in each direction to coat the clutches.

[Scrippy]

FWIW I have done my diff fluid twice. 2nd owner at 25,000 and now at 245,XXX. No diff issues yet but I have replace the velocity joint because I had a vibration on hard pulls. I agree that you just drive it and see what happens. I’m not casting dispersions on your shop but very few shops know the internals of our diffs like a boss despite what they may claim.

[BrutalS65]

Originally Posted by DukeofAlexandria

This.^

Also, you gave us zero info on your car that matters. Year, mileage, history of racing/dogging the car?

-Duke

My bad, she’s a 2011, 46k miles on the clock with previous 2 owners. 1st owner put down the majority of the mileage, second owner just bought it as an investment and only drove it 4k miles in 4 years. All service stamps are recorded.

My guesses are the 1st owner thoroughly enjoyed the car. I know the second owner was a detailer and only took the car out to service and then clean every week in the garage when his mrs had a go at him. He also had an RS5 as well as an E46 M3 track car.

[BrutalS65]

Originally Posted by BP709

What fluid did you use? There is a bmw service information bulletin that addresses the exact noise you’ve experienced. Drain and refill the diff with XJ w/FM booster and then go drive the car slow tight circles in each direction to coat the clutches.

I believe my specialist has done this, even then I did drive in tight circles myself.

[Rober84m]

I had this issue when I first got the car brand new back in 2011. It annoyed me a lot and took it to the dealership and they took care of it under warranty.

Please read below:

This Service Information bulletin supersedes SI B33 01 02 dated March 2008.

SUBJECT
Grinding Noise from the Differential during Slow Cornering

MODEL
E90, E92 and E93 M3 from start of production

SITUATION
A grinding noise may be heard coming from the differential during slow cornering. This noise is best heard during tight cornering situations; for example, while parallel parking, driving in a tight circle, etc.

CAUSE
When the rear wheel speed differential varies during tight cornering, a slip stick effect is created on the lining and steel discs incorporated in the differential locking clutch, causing the grinding noise. This noise typically goes away as the locking clutch discs in the differential are broken in.
The break-in time varies depending on driving habits; for example, tighter cornering (working the locking clutch) means that it takes less time to break in the locking clutch discs.

CORRECTION
If a customer complaint is verified as described above on the E46 M3; E60 M5; E63 and E64 M6; or on the E90, E92 and E93 M3 vehicles, the differential oil should be replaced with a specially formulated differential oil, BMW part number 83 22 2 282 583.
PROCEDURE
1. Drain the differential oil. Refer to the appropriate model repair instruction in TIS:
Main Group 33 / Subgroup 10 / RA 0011259.
2. Refill the differential with special differential oil as shown in the illustration below.
Differential fill capacity = 1.2 liters (1.3 quarts).
3. Road test the vehicle.
With the vehicle at operating temperature, drive in tight circles (20 circles in each direction), allowing the special oil to coat the locking clutch discs.
The grinding noise will decrease when the locking clutch discs are sufficiently coated. Some slight noises may still be heard after driving in tight circles. Advise the customer that it will be necessary to drive the vehicle up to 600 miles before all noises are eliminated.
Note: Vehicles that have had the differential oil converted to this special oil should continue to use this oil whenever a service requiring the differential oil replacement is indicated.

[chocstraw]

I had a bit of noise with my carmax purchased E92 and drained some weird green fluid from the diff and put plain castrol SAF+XJ+FM and it helped a bit.

I'll be rebuilding it with the racingdiffs kit soon and will update if I get faster lockup / more enjoyable driving experience.

[PACarGuy]

I had that same grinding noise in low speed tight turns in my diff after a track day in 2018 and the dealer replaced the whole diff under an aftermarket warranty. Fluid change didn't make any difference and I found it annoying.

Recently I was talking to my indy shop and he laughed a bit and said that dealer techs aren't really allowed to open up diffs and just end up replacing the whole unit, whereas he could have rebuilt it. As you noted, a good used diff is also a good option as well.

[kyrix1st]

Use Motul competition 75W140 LS and change every few thousand miles. I managed to flush the system well enough and experienced no more noises with my high mileage 6MT. It's also normal for a diff to generate more particles.