[delta]

Originally Posted by ashmostro

Any updates to this mystery, Delta?

Good timing, ashmostro! I was about to post per below.

Got the M5 back from my dealer last Friday (Oct 29). Prior to the tech taking my car back into the shop, I was able to replicate the thud/shudder "event" once, as I sat in the drive-up service bay with both my Shop Foreman and Service Advisor in the car. They both said to me that they heard and felt something just after ignition cut-off. However, I told them that not all events I experienced had occurred with the same degree of intensity. This time, it happened to be on the moderate side, i.e., less noise and less shudder. At least they said they both heard and felt what I was trying to explain.

As part of their inspection, they called in a regional factory rep. They also compared my car to another M5 F90 that they fortunately had at the time. They were unable to duplicate the event, and found my car to be operating the same as the other M5. No fault codes were stored for the differential, either resident or in the past. They did remark that the car's multi-disc clutch packs release when the car is turned off. (I sensed that this may be the case, i.e., an "unloading" of some sort.) It appears that this is all that they are able to do.

In the end, I wasn't surprised (and thankful, actually) that nothing could be found. The event has been a matter of record, at least if and until something" occurs that hampers performance, causes part breakage, etc., and is something that I will have to live with. To use my son's expression, "I'm not trippin'."

[SenorFunkyPants]

With the "hand" brake off and auto hold off, the car will tend to creep forwards, so there is an amount of energy held in the drive train when stationary that will be released when the engine is switched off.
Any play in the drivetrain might then reveal itself as a clunk or shudder as the load on it is released.
I guess the engine idle speed is as expected?
As a data point my 2019 car doesn't have the same characteristic.

[ashmostro]

Good to hear and thanks for the update delta! Hopefully it’s a “within spec” issue and as you say, you are now on the record if something were to happen in the future.

[delta]

Originally Posted by SenorFunkyPants

With the "hand" brake off and auto hold off, the car will tend to creep forwards, so there is an amount of energy held in the drive train when stationary that will be released when the engine is switched off.
Any play in the drivetrain might then reveal itself as a clunk or shudder as the load on it is released.
I guess the engine idle speed is as expected?
As a data point my 2019 car doesn't have the same characteristic.

Appreciate your comments. (Great nick, BTW.)

From the sound and vibration, I also think there is a release of energy somewhere. The only puzzling part is the fact that most F90's do not appear to demonstrate this particular thud/shudder characteristic. Luck of the draw.

[lemetier]

Originally Posted by delta

Appreciate your comments. (Great nick, BTW.)

From the sound and vibration, I also think there is a release of energy somewhere. The only puzzling part is the fact that most F90's do not appear to demonstrate this particular thud/shudder characteristic. Luck of the draw.

Do you have a spot where where this occurs somewhat consistently? I see references to inclines as a common theme but haven't seen whether a turning maneuver is involved as well. I suggest trying this shutdown method to eliminate any driveline sag.

Before removing pressure from the brake pedal:

- Engage the parking brake via the switch. Auto Hold uses the service brakes with the engine running; not the parking brake as eluded to up thread. If using Auto Hold, there is a change-over from the service brakes to the parking brake at shutdown.

- Select P on the gear selector to engage the parking pawl on the transmission.

- Ignition: off

[delta]

Originally Posted by lemetier

Do you have a spot where where this occurs somewhat consistently? I see references to inclines as a common theme but haven't seen whether a turning maneuver is involved as well. I suggest trying this shutdown method to eliminate any driveline sag.

Before removing pressure from the brake pedal:

- Engage the parking brake via the switch. Auto Hold uses the service brakes with the engine running; not the parking brake as eluded to up thread. If using Auto Hold, there is a change-over from the service brakes to the parking brake at shutdown.

- Select P on the gear selector to engage the parking pawl on the transmission.

- Ignition: off

The "event" as I now call it (thud/thunk/shudder) does not occur every time I shut off the ignition. When it does occur, it does so randomly, i.e., it may occur twice in a row or go a few days without one occurrence.

On your point about inclined surfaces, the event does seem to have a vague relationship to inclined surfaces or just after climbing an inclined surface. For example, it occurs more often just after I have traveled up and remain on an incline (parking on a hill) or entering my garage (inclined driveway). In the former example (i.e., parking on a hill) my wheels were turned to the left before shutdown when the event occurred.

Any relationship between the event and the brakes I have yet to fully sort out. I have tried to isolate the relationship between shutdown and applying/not applying the brake pedal, parking brake or Auto Hold prior to shutdown. I have tried your suggested sequence a few times; I remember at least one occurrence under those circumstances. One sequence I do not remember trying is to cut off the ignition in "D," just after stopping and after releasing the footbrake. Gotta try that.

Appreciate your thoughts. (In regard to the parking brake vs. Auto Hold, I did not know that the function uses the regular brakes rather than the parking brake. Good to know.)

[wesleyan92]

Originally Posted by delta

Good timing, ashmostro! I was about to post per below.

Got the M5 back from my dealer last Friday (Oct 29). Prior to the tech taking my car back into the shop, I was able to replicate the thud/shudder "event" once, as I sat in the drive-up service bay with both my Shop Foreman and Service Advisor in the car. They both said to me that they heard and felt something just after ignition cut-off. However, I told them that not all events I experienced had occurred with the same degree of intensity. This time, it happened to be on the moderate side, i.e., less noise and less shudder. At least they said they both heard and felt what I was trying to explain.

As part of their inspection, they called in a regional factory rep. They also compared my car to another M5 F90 that they fortunately had at the time. They were unable to duplicate the event, and found my car to be operating the same as the other M5. No fault codes were stored for the differential, either resident or in the past. They did remark that the car's multi-disc clutch packs release when the car is turned off. (I sensed that this may be the case, i.e., an "unloading" of some sort.) It appears that this is all that they are able to do.

In the end, I wasn't surprised (and thankful, actually) that nothing could be found. The event has been a matter of record, at least if and until something" occurs that hampers performance, causes part breakage, etc., and is something that I will have to live with. To use my son's expression, "I'm not trippin'."

Thank you for doing the investigative work for all of on the same boat.

I will no longer be trippin, either 🙂

[delta]

Originally Posted by wesleyan92

Thank you for doing the investigative work for all of on the same boat.

I will no longer be trippin, either 🙂

You're very welcome, and I'll add that it's a team effort! I received lots of info here, much of which I passed on to the techs. Many minds....

[neoprufrok]

Just got my 2021 M5 Comp and this happens for me too.

[delta]

Originally Posted by neoprufrok

Just got my 2021 M5 Comp and this happens for me too.

What is your M5's build date, neoprufrok? I'm tracking the build dates of those on this thread who are having the same issue.

Thanks.