Need help diagnosing a "clunk" when braking quickly

pgolimowski · #1 01-10-2012, 03:03 PM

I have an 08 x5 4.8 with about 45k miles. Only have had this car for a few months so I'm not sure how long this has been going on. When I push the brakes slowly, it brakes normally. If I push them quickly, but not necessarily hard, it makes a loud clunking noise that can be heard and felt in the pedal. Before my warranty ran out I had dropped it off for service and had them check the brakes and they said they were normal. This is about my 10th BMW and this can't be normal. Any ideas of what to check would be appreciated.
Thanks
Patrick

seattle · #2 01-10-2012, 03:31 PM

Sounds like ABS engaging.
In my E70, ABS usually enages with similar clunking and pedal feel in snow or ice, but not on dry or wet pavement.

jbond007 · #3 01-10-2012, 03:35 PM

Are you sure it is brakes? Do you feel it through the whole car? Or is it the often mentioned hard down shift of the transmission returning from 2nd to 1st gear? I was having this happen with harder braking as I would come to a stop before the transmission had shifted back to 1st and "clunk", it would catch up.

Resetting the "Adaptations" in the transmission and trans software upgrade and no lurch or clunk now.

seattle · #4 01-10-2012, 04:53 PM

Quote:

Originally Posted by jbond007

Resetting the Adaptions in the transmission and trans software upgrade and no lurch or clunk now.

Could you elaborate on that? Are you talking about the 10-second holding power button + brake pedal trick?

jbond007 · #5 01-10-2012, 05:20 PM

Quote:

Originally Posted by seattle

Could you elaborate on that? Are you talking about the 10-second holding power button + brake pedal trick?

No. I didn't even know about that one. I had the "Adaptations" (or fluid life sensors) in the transfer case and transmission reset by my mechanic. Has to be hooked up to the computer. I'm not talking about the adaptive programming (to your driving style). Someone else may know more. There are settings that change in the trans logic. It needs to be zeroed out if the fluid is changed or if it's clunking or lurching.

That, along with an hour of software updates, fixed my extremely hard downshift issue. If you're in the puget sound area, I went to Broadstroke Associates in snohomish county. The best $180 I've spent.

pgolimowski · #6 01-10-2012, 03:41 PM

Could be ABS, not sure. It is just 1 loud clunk and then normal braking. Like if I stab the brakes quickly. If I remember right abs was more like a pulsing.

pgolimowski · #7 01-10-2012, 03:44 PM

Thanks jbond, I was thinking it was the brakes or a sudden weight transfer on a worn out bushing or something but I'll check the tranny. I'll drive home from work tonight and test it with the car in N. Should help rule the transmition out or not.

chiefneil · #8 01-10-2012, 05:23 PM

Could it be the brake assist feature? I notice a clunk sound too in my '12, but it's generally when I very quickly release the gas and hit the brakes. Not necessarily a hard panic stop but a very quick transition to braking.

Brake assist is supposed to boost braking pressure in emergency situations.

pgolimowski · #9 01-10-2012, 05:31 PM

Chiefneil, that sounds like a possibility. I'll try it without lifting off the gas and with and see if there is a difference.

rabenoja · #10 01-11-2012, 04:01 AM

I didn't have the clunk noise but my service advisor (who is a friend) says that the clunk is a result of worn bushings. He had the tech check mine since I was coming out of warranty and they were worn so he had them replaced. On my paperwork, he put "customer hears clunk while braking" as the complaint to get the diagnosis.