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09-20-2006, 04:50 PM
As some of you may recall, I was experiencing a clunk from the front brakes when coming to a slow stop at speeds under 5mph. This only happened then, and never at speed (coming to a normal stop, etc) - it would only happen when pulling into the garage or going through a drive through where you are slowly stop and go for a bit.

Last weekend I decided to get to the bottom of it and examined the front rotors in detail - I thought I'd share what I found.

First, I discovered that drive side front rotor did not do it. This is easy to diagnose - jack the driver front side up, spin the wheel and have someone gently apply the brake. If it clunks, it will clunk loudly right in your face. :)

The passenger side did clunk - spin the wheel, slow application of the brake pedal resulted in a clunk.

I took the caliper off of the car, removed the pads and found that the inboard pad has 3 little spring teeth that fit neatly into the piston. I spread these a little bit, cleaned the caliper and caliper mounts, re-greased the contact points and put it all together.

Repeated the experiment clunked, but much less. Hmmm...

Took it apart again, and this time I spread the prongs on the outboard pad retaining clip to give them a bit more clamping force once installed.

Put it all together, tried again clunk!

I was thrilled for about 30 minutes - took the car out, everything was fine, but it started doing it again. Went to a local Jack In the Box where it always clunks and it was there but much improved.

So, I'm thinking that one of two things is happening here - the inboard pad springs are loosening up a bit with use and the pad is sticking just slightly, so that under slow speed stops, the piston and pad are not completely "mated" and the piston is smacking the back of the pad as it sticks to the rotor. Once underway, the rotation of the rotor frees the pad and it returns to it's normal "mated" position with the piston. This is theory 1 at the moment.

The other theory is that the outboard pad retaining spring was faulty to begin with and wasn't seating tightly enough to keep the caliper from slapping a bit under braking. If you have someone apply the brake when you have the outboard retaining spring off of the car you will see that the caliper will move around and clunk exactly like what I've described, but about 50% louder.

I've ordered a new outboard pad retaining spring from BMW and we'll see if that fixes it.

A few other random theories :

1. The Z4M and several other '07 BMW models have the new Brake Assist feature which, when taking your foot quickly off the gas, gently nudges the pads up against the rotor to minimize time required for full braking power in an emergency - someone at BMW told me that their 5 series does what sounds like the same exact thing clunk wise, but we didn't touch the throttle during our tests and it was clunking.

2. Air in the lines - haven't bled the front brakes yet but will do so when I swap out the retaining spring. Very unlikely that this would cause a pad to stick, but easy enough to rule out as a cause.

3. Brakes haven't bed properly - I know this isn't the case. The brakes were bed at around 200 miles and this is something I've done in the past several times with many cars over the years. This car bed very nicely and the front rotors have a wonderful layer of even pad material all of the rotors.

Anyhow, sorry for the long ramble - I hope if anyone else expereinces this little clunk this will be of some assistance. :) I'll make an update after the next weekend when I replace the retaining clip.

09-20-2006, 09:52 PM
Thanks for this - no clunk with mine yet, but at least I'll have a clue if/when it appears!

09-20-2006, 10:38 PM
noticed the pad knock at low speed right away...gonna drive it for a while and if it is still present at the breakin service interval then I will mention it...not a big deal but somewhat annoying.

09-21-2006, 12:59 AM
I'd say it's good to know that others are doing it, but it can be annoying enough that I don't wish it on anyone else! :)

It happens mostly in just 3 cases for me :

1. Drive-thrus (it's exasberated by the close wall of the store next to the car too and, of course, you have your window down)

2. Pulling in the garage and coming to a nice slow stop (easily fixed by screaming balls out into the garage and slamming on the brakes)

3. Backing up from a parking spot in a tight parking lot - back up slow, gently apply the brake...."CLUNK!"

Forgot to mention, you can feel this through the brake pedal as well when it happens - you won't mistake it if it happens with your car.

I just had my 1200 mile inspection done yesterday and decicded not to mention it. I know, sounds crazy and redicutarded...but I've had dealerships ruin several wheels in the past and, with the Z4M wheels being so virgin, I just can't bring myself to justify a potentially ruined wheel by letting them take them off (a refinished wheel is typically never as good as the virgin wheel).

I know I'll be super gentle when I remove the wheels, and I'm just kinda curious about such things and want to figure out what it is on my own. If they can't replicate an issue after trying just one slow stop, they will say simply "Sorry, sounds fine to me" and that's fair given how busy they are.

I, on the other hand, have some time on my hands these days being recently retired so I'm playing grease monkey in my spare time. :)

09-24-2006, 11:50 AM
let me know if the new retaining spring fixes this annoying pad knock...thanks!

09-27-2006, 06:15 AM
I replaced the passenger side pad retaining clip with a new one and bled the front brakes thoroughly (a surprising amount of trapped air for a new car with 1500 miles).

Took it out tonight and it's still there - clunk. For some reason it is certainly less pronounced than it was before, and that happened the first time I had the caliper apart so that's a bit odd to me. Something is shifting over time and flexing it seems.

I'm certain it's passenger side only - jack the driver side up, spin the wheel and have someone brake. Perfect, quiet.

Do the same thing on the passenger side...CLUNK. And you can feel it through the brake pedal.

I'm going to give the car another 1000 miles or so and see if I can't figure it out still (or see if it will just remedy itself, always the best fix).

The only real difference between the passenger and driver side caliper that I can see is that the drivers side has the pad wear indicator wire buried in the inboard pad - that's it. Everything else is the same (no apparent polarity conflicts where something would be flipped for the passenger side and perhaps making noise)

09-27-2006, 10:53 AM
a manufacruring defect causing a mechanical sound from the pad shifting...

11-17-2006, 12:16 AM
I have this on my M Coupe. I have less than 400 miles. Same clunking sounds, at low speed when coming to a stop.

My production month/year is: 7/2006


11-17-2006, 12:46 PM

11-21-2006, 09:35 PM

11-22-2006, 09:30 PM
I purchased a Z4 coupe and this is the 3rd time it has been at the dealership. The engine is giving me problems and I only have 1919 miles on it. The first time there was a metal sound when starting the car. It sounded as if there was not enough oil. BMW said it was normal. THe second time all my braking system lights turned on and the noise was now louder. It was a extemely noticable sound that would make people look as you came to a stop. When BMW looked at it they determined that the lifters were bad and had to be replaced. # lifters were replaced. This weekend I turned it on again and the same sound returned. BMW now said it was the other three lifters. I was just notified yesterday that the entire top portion of the engine needs to be replaced. Wow! Have any of you had this similar problem?

11-23-2006, 04:09 AM

11-26-2006, 11:45 AM
I just leased a new m roadster on 11-20-06, immediately heard the clunking noise upon slow speed braking, also can feel it through the pedal. Dealer re-torqued the under body difusser plate, re-torqued the under the hood "sway bars". No luck. Took to another dealer, front wheels removed, brakes inspected and greased, a little better, but still obvious.

Tomorrow (11-27) will take it back. Afte reading these posts, it appears obvious to me that BMW doesn't yet have a fix. As the car has 215 miles on it, I am thinking about trying to return it (for another?) or attempt to get them to buy it back. According to Calif. lemon law, car must be at the dealer 4 times with no resolution to invoke the lemon law....I believe that this is one of those situations that will not soon be resolved. I actually may talk to a lemon law attorney tomorrow. Otherwise, no problems, and I was looking forward to break in period being finished, as I can feel this engine wants to I am not so sure.

11-26-2006, 06:03 PM
I have 2K miles now and it is much better, and much less noticeable after regreasing the contact points in the calipers and on the pads.

It does happen from time to time at a drive through, but that's the only time it happens. The car is SO good that I'd put up with it doing it all the time probably. Thankfully it's only once in a while and now with 2K on the clock, it's so frequent that I have all but forgotten about it.

When I had 600~1300 miles on the car it was pretty bad though.

02-17-2007, 02:47 AM

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