Knocking sound when braking

CeEl · 05-15-2012, 12:28 PM

Just took delivery of my new Z4 yesterday. On my way home, I hear a knocking sound from the rear when I brake moderately. Doesn't happen when I brake lightly (stop and go traffic) nor does it happen when I brake hard. I heard it only once or twice.

Later, took the car for a spin and was able to replicate the sound easily.

Left the Z4 at home and took my other car to work since it's worrisome ...

Dealer didn't offer any suggestions, just asked me to bring it in tomorrow - they will take a ride with me and listen.

The knocking starts when I brake, the intervals between the knocks get longer as the car slows down and stops when the car comes to a stop. It comes from the rear. Didn't see anything obvious wrong with wheel or tire. Car brakes just fine - just the noise.

I searched the forum, but all other noises from the rear seem to be of the "thunk" kind and only over road imperfections.

Anybody any idea?

army_men · 05-15-2012, 01:58 PM

And you are sure it's not just the ABS kicking in? do you feel feedback on the break pedal?

CeEl · 05-15-2012, 02:22 PM

Quote:

Originally Posted by army_men

And you are sure it's not just the ABS kicking in? do you feel feedback on the break pedal?

No pulsating on the brake pedal...

The vehicle comes to a stop smoothly.

z4z4z4 · 05-16-2012, 03:22 AM

Try to replicate it in reverse.

CeEl · 05-16-2012, 05:32 AM

Quote:

Originally Posted by z4z4z4

Try to replicate it in reverse.

Ok, will try. Do you have a hunch what it could be?

Didn't drive at all yesterday -- afraid to make whatever it is wrong worse. But have to drive today -- to the dealer.

CeEl · 05-17-2012, 12:12 PM

Dropped the car off yesterday evening. Tech drove it with me in the passenger's seat. Sure enough the thump-thump-thump happened ( I am still not sure whether to call it a knocking noise instead). Tech agreed it wasn't normal. First he thought rust maybe but then I told him the car just came off the boat and didn't stand on a dealers lot for months. He guessed something with the brake calipers maybe but that they would need to check it out.

They haven't called back yet today... Hope it's not a case of "we need to order the part from Germany and it will take 2 months"!

CeEl · 05-17-2012, 08:27 PM

Tech put graphite (?) on the brake pads and determined it was the brake pad. They replaced it ... will probably pick the car up tomorrow. Not quite sure what was actually wrong, some "infant death" issue?

CeEl · 05-18-2012, 03:28 PM

Brake pad. Material failure. They replaced it and all is good!

They gave me a free cap and a bottle of oil for the trouble.

05-15-2012, 12:28 PM	#1
CeEl Major 479 Rep 1,252 Posts Drives: 2020 Z4 M40i Join Date: Sep 2009 Location: Ohio iTrader: (0) Garage List 2024 BMW X5 M60 [0.00]	Knocking sound when braking Just took delivery of my new Z4 yesterday. On my way home, I hear a knocking sound from the rear when I brake moderately. Doesn't happen when I brake lightly (stop and go traffic) nor does it happen when I brake hard. I heard it only once or twice. Later, took the car for a spin and was able to replicate the sound easily. Left the Z4 at home and took my other car to work since it's worrisome ... Dealer didn't offer any suggestions, just asked me to bring it in tomorrow - they will take a ride with me and listen. The knocking starts when I brake, the intervals between the knocks get longer as the car slows down and stops when the car comes to a stop. It comes from the rear. Didn't see anything obvious wrong with wheel or tire. Car brakes just fine - just the noise. I searched the forum, but all other noises from the rear seem to be of the "thunk" kind and only over road imperfections. Anybody any idea?
	Appreciate 0 Tweet Quote

05-15-2012, 01:58 PM	#2
army_men Lieutenant 45 Rep 406 Posts Drives: E89 Z4 35i Join Date: Jan 2012 Location: Canada iTrader: (0) Garage List 2011 BMW Z4 35i [10.00]	And you are sure it's not just the ABS kicking in? do you feel feedback on the break pedal? __________________
	Appreciate 0 Quote

05-16-2012, 03:22 AM	#4
z4z4z4 Lieutenant 45 Rep 547 Posts Drives: 2002 M3 Join Date: Mar 2010 Location: mild mediterranean breezes iTrader: (1)	Try to replicate it in reverse. __________________ Sold 2011 Z4, kept 2002 M3 PM for various e89 parts 4sale.
	Appreciate 0 Quote

05-17-2012, 12:12 PM	#6
CeEl Major 479 Rep 1,252 Posts Drives: 2020 Z4 M40i Join Date: Sep 2009 Location: Ohio iTrader: (0) Garage List 2024 BMW X5 M60 [0.00]	Dropped the car off yesterday evening. Tech drove it with me in the passenger's seat. Sure enough the thump-thump-thump happened ( I am still not sure whether to call it a knocking noise instead). Tech agreed it wasn't normal. First he thought rust maybe but then I told him the car just came off the boat and didn't stand on a dealers lot for months. He guessed something with the brake calipers maybe but that they would need to check it out. They haven't called back yet today... Hope it's not a case of "we need to order the part from Germany and it will take 2 months"!
	Appreciate 0 Quote

05-17-2012, 08:27 PM	#7
CeEl Major 479 Rep 1,252 Posts Drives: 2020 Z4 M40i Join Date: Sep 2009 Location: Ohio iTrader: (0) Garage List 2024 BMW X5 M60 [0.00]	Tech put graphite (?) on the brake pads and determined it was the brake pad. They replaced it ... will probably pick the car up tomorrow. Not quite sure what was actually wrong, some "infant death" issue?
	Appreciate 0 Quote

05-18-2012, 03:28 PM	#8
CeEl Major 479 Rep 1,252 Posts Drives: 2020 Z4 M40i Join Date: Sep 2009 Location: Ohio iTrader: (0) Garage List 2024 BMW X5 M60 [0.00]	Brake pad. Material failure. They replaced it and all is good! They gave me a free cap and a bottle of oil for the trouble.
	Appreciate 0 Quote