10-01-2021, 12:53 AM | #1 |
Private First Class
29
Rep 105
Posts |
Question: "Clunk and shudder" at shut-down: The M Rear Axle Differential Lock?
Picked up a '21 LCI. First M5. I now have just over 2K miles. Enjoying the heck out of it.
But, as I've been getting used to the sounds and operating characteristics that any new ride presents, I've been noticing that when I shut off the ignition, I often get a one-time, audible "clunk" sound coming from the rear of the car. Not a loud nor metallic sound, but one that is definitely audible. Just a dull, summary clunk that I distinctly hear coming from the rear trunk/below trunk area just after pushing the engine start button to shut-off. Perhaps as important a clue, the sound is accompanied by an abrupt shudder that I can feel through the driver's seat. The noise and accompanying shudder does not occur every time. When I shut off the car on a level surface, it rarely occurs; but, I've noticed that if I shut off on an incline, or just after driving up an inclined surface to a level surface, and then shut off the ignition, I almost always, if not always, hear that "clunk" and hopefully benign, accompanying shudder. --Is the "clunk" and accompanying shudder related to some kind of unloading of the M5's M rear axle differential lock? --Is it some type of lock-up tension suddenly released from the differential at the time of ignition shut-off? --Possibly an issue with the diffy's lock control unit? I am not concerned at this point; Perhaps I should... TIA! |
10-01-2021, 08:51 AM | #2 |
Second Lieutenant
228
Rep 294
Posts |
Just a thought, to eliminate a possibility.
While holding the brake down, put the emergency brake on, then put into park, then release the normal foot brake. Just wondering if its the tranny holding the weight when on a incline. |
Appreciate
0
|
10-01-2021, 12:38 PM | #3 | |
Private First Class
29
Rep 105
Posts |
Quote:
Thanks for the thought though, Danny. |
|
Appreciate
0
|
10-02-2021, 10:20 AM | #4 |
Private First Class
29
Rep 105
Posts |
Hey folks,
Any other comments here on my shut-off shudder issue? Normal behavior? A problem brewing? I'm new to this M5 community, but not to M. That said, this one has me stumped. My gut sez this is a normal operating characteristic, but would like confirmation. Opinions would be appreciated. (And thanks again, Danny.) ...terry |
Appreciate
0
|
10-05-2021, 10:36 PM | #5 | |
Captain
286
Rep 603
Posts |
Quote:
|
|
Appreciate
0
|
10-07-2021, 11:54 AM | #6 |
Private First Class
29
Rep 105
Posts |
Appreciate the watchful input. Having awareness in this regard (i.e., noticing when something is amiss car-wise) is certainly a plus.
|
Appreciate
0
|
10-07-2021, 11:43 PM | #7 | ||
Private
45
Rep 69
Posts |
Quote:
Quote:
For our M5s, mine also being a 2021, If you put the car in it's sportiest settings and tap the throttle just a tiny bit, the entire car shutters. The same effect happens when the fuel is cut off when you shut it down. This was also relevant in my 2019 comp. I know it seems weird but it really is normal. |
||
Appreciate
1
omgmike358.00 |
10-08-2021, 01:37 AM | #8 | |
Private First Class
29
Rep 105
Posts |
Quote:
So, I gotta go once again with those who know. Appreciate your thoughts. |
|
Appreciate
0
|
10-09-2021, 10:54 AM | #9 |
Brigadier General
1247
Rep 4,088
Posts |
What is your shutdown sequence? Is your foot on the brake pedal? Do you use the auto-hold feature all the time? Do you apply the parking brake before you shut down the car or let the car apply it on its own?
The rear parking brake with automechanical actuation is used for a lot of things, including auto-hold, short-term false “Park” when left idling for a long time until the transmission truly engages Park several minutes later. All of these things can be and often are audible and felt. |
Appreciate
0
|
10-10-2021, 07:02 AM | #10 |
Captain
1345
Rep 848
Posts
Drives: M8 GC || M5 Comp || X7 40i
Join Date: Jul 2016
Location: USA
|
OP - this is exactly the same thing happening in my 21 LCI. This has nothing with the sequence of shutting down. There is definitely something going on in the rear and it is not consistently happening every time but more so than not.
I'll ask my service advisor during the next check in. This never happened in my 2019 pre-LCI. I posted it earlier in the year after having the car for a month or so - see my third point: https://f90.bimmerpost.com/forums/sh....php?t=1834085
__________________
2024 M8 GC Black/Black || 2021 M5 Carbon Black/Midrand beige || 2021 X7 40i Amertin metallic with Ivory white merino
2019 M5 F90 || 2018 X5 s35i || 2017 M5 F10 with Arkapovic Exhaust || 2016 535 || 2012 535 hated it after the E60 || 2010 535 E60 - my fav || 2008 528 E60 my first |
Appreciate
1
omgmike358.00 |
10-10-2021, 01:11 PM | #11 | |
Private First Class
29
Rep 105
Posts |
Quote:
I have tried numerous sequences in a quest to isolate the problem. I cut the ignition first with the brake pedal on and with the brake pedal off; I applied the parking brake before cutting the ignition, and I tried the various sequences with the auto-hold on and off before cutting the ignition. I concluded that ignition cut-off, with or without the presence of the foot brake, parking brake or auto-hold, was the initiator of the problem sound. |
|
Appreciate
0
|
10-10-2021, 01:13 PM | #12 |
Brigadier General
1247
Rep 4,088
Posts |
Thanks.
In that case, the first thing I’d suggest is to ask your dealer to check the rear parking brake and potentially reset/adjust it. It might not be functioning within spec. Good luck and let us know what turns up! |
Appreciate
0
|
10-10-2021, 02:11 PM | #13 | |
Private First Class
29
Rep 105
Posts |
Quote:
wesleyan92 remarked: "Also, when I turn the car off, 50% of the time, I feel a clunk/thud in my rear end coming from the bottom of the car. Super weird." PunjabiM3 remarked: "I have had mine since Jan 2nd and have also been experiencing this thud coming from the rear when putting the car into park. I wonder if perhaps there is something wrong with the rear diff? What is the build date on your car? Please post if you figure out what it is coming from, I have thought about taking the car to have it looked at but it is periodic and nothing that sounds bad, at least not yet." While three positive responses (including mine) doesn't a definite survey trend make, the issue is rather unusual and worthy of at least a raised eyebrow or two. Something is definitely happening in the M5's rear drivetrain/parking brake componentry just after ignition cut-off. What is it? At this point, I'll be following your strategy for now, i.e., "...it's not that bad, is not getting worse, and doesn't impact any performance or operation." That said, though I just brought the car in for its 1200 mile break-in a few weeks back, I plan to check back in with the dealer to make this seemingly innocuous issue a matter of record. You know. Just in case... My build date is April/2021, BTW. Last edited by delta; 10-10-2021 at 02:22 PM.. Reason: Added the possibility of a maladjusted parking brake |
|
Appreciate
0
|
10-10-2021, 02:17 PM | #14 |
Private First Class
29
Rep 105
Posts |
Per my last post above, I plan to bring the car in shortly. Your point is well-taken and certainly a possible suspect. I will definitely make sure to add a parking brake function check into my problem description at check-in. Thx.
|
Appreciate
0
|
10-10-2021, 07:22 PM | #15 | |
Captain
1345
Rep 848
Posts
Drives: M8 GC || M5 Comp || X7 40i
Join Date: Jul 2016
Location: USA
|
Quote:
OP - my build date was March 2021.
__________________
2024 M8 GC Black/Black || 2021 M5 Carbon Black/Midrand beige || 2021 X7 40i Amertin metallic with Ivory white merino
2019 M5 F90 || 2018 X5 s35i || 2017 M5 F10 with Arkapovic Exhaust || 2016 535 || 2012 535 hated it after the E60 || 2010 535 E60 - my fav || 2008 528 E60 my first |
|
Appreciate
0
|
10-11-2021, 12:00 PM | #16 | |
Private First Class
29
Rep 105
Posts |
Quote:
Both the rear differential and the parking brake are electronic-activated. The M Active Differential is in a league all its own, with many input variables contributing to "lock" based on software and its electronic-mechanically operated multi-disc clutch. Is it possible that a premature/maladjusted parking brake is holding off the rear differential via its lock control unit from "relaxing" at ignition cut-off? Is there tension in the differential that should have been electronically "released" once the car is stopped, just prior to ignition cut-off? [Admission: Though I've worked on domestic rear differentials, I have little knowledge of how the M5's differential really operates.] I still think the rear differential is the source of the sound/shudder at cut-off, but am unsure of whether the parking brake may be the actual initiator somehow. The fact the event doesn't happen every time throws me a little, as does the fact that the sound/shudder occurs without touching the parking brake; but, the electro-mechanical nature of both systems and a possible relationship between the two is why I couldn't ignore the possibility. Just my $.02. |
|
Appreciate
0
|
10-11-2021, 03:33 PM | #18 |
Private First Class
29
Rep 105
Posts |
|
Appreciate
0
|
10-11-2021, 04:02 PM | #19 |
Brigadier General
1247
Rep 4,088
Posts |
One more thought. It's possible an uneven adjustment of the parking brake between the two rear axles could lead to a literal differential torque upon shutdown, which could then be making the diff groan because it's not expecting any relative (and therefore, internal) motion.
|
Appreciate
0
|
10-11-2021, 05:08 PM | #20 | |
Private First Class
29
Rep 105
Posts |
Quote:
Appreciate your digging into the matter. Very interested to see what the dealer will say. And I will definitely share the results. |
|
Appreciate
0
|
Post Reply |
Bookmarks |
Thread Tools | Search this Thread |
|
|