Troubleshooting a mild ker-thunk at lower speeds

[pachieh]

I've been trying to narrow this one down for a bit...

BL: I get a mild ker-thunk that I can feel and slightly hear at lower speeds (10-45mph) under milder acceleration. Transmission shifts fine, engine is not mis-firing (no error codes) and no knock or other shenanigans via logs in BM3. 76k miles.

I started noticing this a few weeks back and it is starting to get annoying. I thought it was a mis-fire at first, but it is seemingly random in when it happens. Not the same RPM range, not the same gear all the time. I inspected under the car (BMW did a thorough scope and look over at a previous service), driveshaft looks fine, no oil leaks from the rear diff or t-case.

When I accelerate hard or go WOT, it doesn't happen either.

I am on xHP, tried a number of maps to see if it was a map issue (to include old versions of maps), but it is not. Same symptoms regardless of the map.

So I'm trying to think what it could be. Still the original suspension too. Wheel bearings? t-case calibration? I do need new tire rods as the bolts holding the mid-points are missing and they are seized at the adjustment (but overall alignment is fine).

Thoughts?

[Mandinca]

I had a similar thing with an Audi I once had......I looked everywhere like you have and somehow the last thing I checked was grabbing the tie rods and heaving on them to see if they rattled. One did.
Make sure you have the wheels suspended (stands, not ramps) and give it a try.
Top hat maybe ?
One last thing, my E88 also used to do something similar, turned out to be a loose subframe bolt.

Good luck with it.

[pachieh]

Dang, didn’t even the ink of something loose in the subframe that needs to be tightened down…

[I Luv BMW]

Had something similar happen to my F86 recently. The "thump" would come from underneath the car and usually at low speed and low RPM. Replaced front driveshaft but this did not solve it. However, the problem seemed to go away after replacing front tyres and wheel balancing and alignment. So maybe check if your tyres are close to needing replacement?

[pachieh]

Small update...

Had new rear tires put on, had the fronts checked for balance, all is ok. Had new front tire rods replaced and an alignment done (toe up front was out of spec), made things a little bit better...

Overall, the thump is still there at lower RPMs on mild acceleration. It almost feels like a misfire or a tranny or engine mount... I haven't had spark plugs replaced in nearly 40k, so it's probably time to try that now too although logs don't show any misfires...

[Oliver Queen]

Hi Pachieh, were you able to figure out what this is? My AMG is doing the same but can't figure out what's going on someone told me it could be the torque converter for the AMG

[pachieh]

Not yet. I have an appt next week to have the transfer case fluid changed and a calibration done… mtf

[pachieh]

UPDATE:

Had the front and rear diff fluid changed and the transfer case re-calibrated (same fluid though) along with changing spark plugs, the issue is still there just a little bit better. Next step is replacing ignition coils (had done this, but had major issues with the Dinan coils with tons of misfires).

If that doesn't work, then I will look at sometime doing a transfer case fluid change. Like usual, dealer said that it's a lifetime fluid (no such thing) and didn't know how to change it without taking the whole t-case out and basically doing a rebuild just to do a fluid change.

MTF.

[dentprotony@gmail.com]

Originally Posted by pachieh

UPDATE:

Had the front and rear diff fluid changed and the transfer case re-calibrated (same fluid though) along with changing spark plugs, the issue is still there just a little bit better. Next step is replacing ignition coils (had done this, but had major issues with the Dinan coils with tons of misfires).

If that doesn't work, then I will look at sometime doing a transfer case fluid change. Like usual, dealer said that it's a lifetime fluid (no such thing) and didn't know how to change it without taking the whole t-case out and basically doing a rebuild just to do a fluid change.

MTF.

Can that be your front driveshaft? Many of my customers report noise/vibration that goes away after front shaft is replaced with an upgraded unit. Maybe look for slack in the tcase splines see if there is excessive play , or maybe remove front shaft completely (10-15 min job) and see if that goes away. Keep us posted

[pachieh]

I guess it is possible, I'll have to get under the car to look on Sunday. No idea how to remove the front shaft, so will be looking for a DIY...

Nevermind, found your video!

Also, since the splines on the transfer case always seem to get worn down too on the front part, worth replacing the spline adapter in the transfer case? Possible to do without taking the transfer case out?

Gotta also hunt down an episodic sound that sounds like sticks in a tin can being shaken... Only happens leaving a stop light (and rarely) in 1st gear or so...

[pachieh]

Video of my front driveshaft… probably a big part of the problem…

https://youtube.com/shorts/XA9CH0RMu...5mUIPg5Q1Mwkbi

[dentprotony@gmail.com]

Originally Posted by pachieh

Video of my front driveshaft… probably a big part of the problem…

https://youtube.com/shorts/XA9CH0RMu...5mUIPg5Q1Mwkbi

That rust on the ujoint is a VERY bad sign. Slack in the splines is rough as well. I would remove the shaft till you can get an upgraded unit. Once the shaft blows up, it will be many thousands in damage and weeks in downtime

[dentprotony@gmail.com]

Originally Posted by pachieh

I guess it is possible, I'll have to get under the car to look on Sunday. No idea how to remove the front shaft, so will be looking for a DIY...

Nevermind, found your video!

Also, since the splines on the transfer case always seem to get worn down too on the front part, worth replacing the spline adapter in the transfer case? Possible to do without taking the transfer case out?

Gotta also hunt down an episodic sound that sounds like sticks in a tin can being shaken... Only happens leaving a stop light (and rarely) in 1st gear or so...

That spline adapter part is not available separately that i know of. Also will need to completely disassemble the tcase to even access it. If you install shaft with longer splines it will fit tight in the unused splines of the tcase and you dont have to worry about anything anymore

[pachieh]

Originally Posted by dentprotony@gmail.com

That rust on the ujoint is a VERY bad sign. Slack in the splines is rough as well. I would remove the shaft till you can get an upgraded unit. Once the shaft blows up, it will be many thousands in damage and weeks in downtime

Dropped you a PM for a quote to get one of yours. How quickly can I get one?

[Slickrick2]

Originally Posted by pachieh

Dropped you a PM for a quote to get one of yours. How quickly can I get one?

Any updates? Curious what was the end result.
Thanks.

[pachieh]

Originally Posted by Slickrick2

Any updates? Curious what was the end result.
Thanks.

It’s installed, still have the issue so now I just need to do a t-case fluid change and recalibration. I was out of town for awhile so it hasn’t been fully fixed yet.

When I take the fuse out for the transfer case, no issues which is why I’m solely focused on that being the issue now. Hopefully the fluid change and recalibration fixes it.

Once I get it done, I will do another thread with a review and mini DIY of everything.

[dentprotony@gmail.com]

Originally Posted by pachieh

It’s installed, still have the issue so now I just need to do a t-case fluid change and recalibration. I was out of town for awhile so it hasn’t been fully fixed yet.

When I take the fuse out for the transfer case, no issues which is why I’m solely focused on that being the issue now. Hopefully the fluid change and recalibration fixes it.

Once I get it done, I will do another thread with a review and mini DIY of everything.

Yes, do the fluid and calibration, this should help big time