"slipping" on acceleration
 

For a little while now, my X is experiencing what I can only describe as a "slipping" vibration - stutter in acceleration, variable in internal. It does not happen at idle, only acceleration. My thoughts:

1. Clutch
2. Rear diff
3. CV

Clutch seems most obvious, but not sure how to confirm other than to replace and hope for the best.

I say rear diff since I also get a slow speed thunk from what appears to the rear/driveshaft, like it is unloading pressure, when coming to a stop or in a slow speed parking lot scenario.

I say CV because I know I have a front right boot tear, but other than that, I do not get any noticeable noise from it. Just letting it run its course until I have no choice but to replace.

Thoughts?

i believe this is called 'clutch chatter' and happens just about on engagement.

rear diff would howl/hum or start to heat up more than usual, and eventually just internally let go and you don't move

cv would click click when loading in a corner

So which do you think it is?

me >? I can't be much of a internet detective. im not in that car. perhaps there's some one you know who can help determine where in the car the noise is coming.

My issue was fixed by replacing my badly worn DISA!

My money would be on the clutch as well, as for how to test that, hmmmm, I'm at a bit of a loss there as well... Maybe try a load in the hatch or trailer, something to add weight to the car\clutch and see if that exaggerates the problem?


I doubt it's the rear diff, mine let go over a period of about a year... yep a year... I couldn't find the hum, he couldn't find the hum, they couldn't find the hum, we couldn't find the hum, the best advice I got was "drive it until something officially breaks and then you'll know" - so I did and it was the diff - glorious mess too...


And I'm thinking probably not the CV because being all wheel drive that would almost be "invisible" as the other three would be pulling the weight, not to mention CVs usually just "pop" or "bang" pretty noticeably and very repeatably under "that" circumstance.


The "thunk" may actually be worn rear body bushings or worn rear control arm bushing, those bushings will often "thunk" under slow speed load changes, like pulling into a parking spot and immediately transitioning into reverse to adjust in the spot - when that arm is forced to "change direction" is when you'll hear \ feel it "thunk" - at least that's my thought anyway and the body bushings will unload at slow downs where you don't come to a complete stop and then accelerate away.

Thanks for the detailed response however my issue was fixed by replacing the DISA unit.

Too funny - I totally see that now :thumbup:


Lad you got her sorted, and so strange, the DISA caused that, good catch and great diagnostic work!

I learned a lot from this web page about DISAs: https://www.eeuroparts.com/blog/disa...s-replacement/ - I'm wondering what is causing my engine to lose power at high RPMs when it gets hot, concurrent with a rough idle at the lights - talking after at least 5 minutes of driving. I had a valve-lift motor problem causing the same issue before, which eventually caused it to not start. I will run an INPA check on it today.

@racebmwm3, glad you got the problem sorted out!