Front brake rattle during LIGHT braking

[xcvii90]

I've searched and came up empty. Maybe I'm missing something, but it seems like lots of people have a problem with their brakes rattling when they are NOT braking, but the rattle goes away when they lightly apply the brakes. My problem is the opposite. No rattle during normal driving, but when I lightly apply brakes, like when I'm slowing down to pace with traffic on a city street, then it sounds like a bad suspension rattle. No vibration or pulsation, only a clunky rattle. The rattle goes away when I get below 30 MPH or if I brake more aggressively.

Car is a 2002 A4 Quattro. I've had the car for a few years and it just started doing this. My first idea was to replace the anti-rattle springs. I picked up some OEM springs from FCP Euro and installed them. No luck. Next I disassembled the brakes and found the mounting bracket on the right was obviously worn where the pads hang on it. The caliper on the right had a rusty piston and a torn boot. So I replaced both front calipers and mounting brackets with refurbished OEM Audi calipers. The bracket mounting bolts and caliper guide pins are torqued to spec and I added blue loctite to keep them from rattling loose. Didn't help.

So I decided to replace the pads next, even though the old pads looked like they had a lot of life left. I used Bosch Quiet Cast ceramic pads. The pads have an arrow on the metal clip that holds the inboard pad to the piston. No help in my Haynes manual or on the Bosch website, but after some research with the Google machine, I decided to install them so the arrow pointed in the direction of disc rotation. Since my calipers are on the rear side of the disc, that would be pointing UP. There were no marks on the outboard pads, so I assumed their position didn't matter. After installation, I found a long, straight country road and bedded the pads with ten medium decelerations and three aggressive decelerations in quick succession followed by a fifteen minute cool down without touching the brakes. To make a long story short, I have plenty of stopping power but new pads didn't help my rattle issue.

Based on recommendations in other posts I will probably try some CRC Disc Brake Quiet next, to attempt to glue the pads to the caliper, but it doesn't seem like this should be necessary. I also have a 2006 A4 Quattro that I bought seven years ago, and I've never had this problem. I replaced the worn brakes with Power Stop pads and rotors and had no issues.

After the Disc Brake Quiet, I will probably move on to new rotors. But I would really like to figure out the issue rather than just throwing money at it and replacing one piece at a time. Has anyone else had a similar issue? Again, the pads DO NOT rattle during normal driving. Any ideas would be greatly appreciated. Right now I'm .

[TobiqueSlang]

do you just hear a rattle or do you feel a rattle in the pedal?

I might be wrong but to me if you're feeling it then that says warped rotors. if it's just a sound though it could be anything, it might not even necessarily be the front brakes.

[Mike Tries]

Bushings or ball joints? Give them a check. They could be flexing and clunking about with all the different forces that you can experience with braking.

[EuroxS4]

Maybe worn CV joint.

[codemode]

Is there a way for you to record it? Are you sure they’re rattling and not clunking? When you say rattle do you mean like a ball in a spray can? Check the sway bar bushings they could cause metal to metal contact. Could you be missing a front engine mount, they can disintegrate.

[Turbo510]

...it sounds like a bad suspension rattle. No vibration or pulsation, only a clunky rattle. The rattle goes away when I get below 30 MPH or if I brake more aggressively.

Something has to be loose to clunk and rattle. I'd probably get the front wheels off (rattle is in front, right?) and then try to grab and shake anything that has the potential to be loose. I've had an annoying rattle that turned out to be a failed sway bar link bushing, so check everything you can.

[walky_talky20]

If you have any "pad rattle" at all, you will know it for sure because it goes away the moment you apply even the lightest amount of brake pedal input. As soon as the caliper squeezes it at all, the rattle will go away. That does not sound like your situation here.

I think what you have is the exact thing my B5 Avant has right now: a loose ball joint somewhere in the front suspension. In my case I believe it is an inner tie rod end. This joint will rattle when you begin light to medium braking. It is being bothered by the minor pulsations from a very slightly warped rotor (or more probably just uneven pad deposits on the rotor). That little bit of extra "grab" with each rotation applies a tiny bit of different forces through the suspension - thus revealing that little bit of slop in one of the *up to 16* ball joints in the front end of an A4 (not exaggerating). If I change to heavier braking, all the rattle goes away instantly. This is because the slight variances in the rotor surface are less meaningful under heavier braking.

Notably it can be difficult to find the offending joint in some cases as the play can often be limited to the "ride height" position in particular. The joint can appear perfectly tight at other positions (for example, with the wheels hanging freely while car is jacked up). This is also the exact situation my B5 Avant is in. A fairly in-depth inspection and test of each joint with wheels hanging revealed no play. Rather than take stuff apart, I've opted for the lazy man's approach: leave it alone until it gets *way worse*, then it should be much more obvious and thus easier to diagnose. This is, of course, not my recommendation at all. You should totally figure your stuff out correctly.

[xcvii90]

Thanks for all of the replies! As an update, I tried applying CRC Disc Brake Quiet to the back of the pads and also bending the tabs on the inboard pads so they grip the piston tighter. No luck.

I don't really feel pedal pulsation from a warped rotor, but replacing rotors is the next thing I'll try.

I've tried wiggling all suspension links and banging with a rubber mallet, and I can't detect any play anywhere. But as walky_talky20 said, it could very well be ride height sensitive. So if it is that, I will probably live with it until it gets bad enough that I can find the problem. I did check the sway bar links as Turbo510 suggested, and the bushings look pretty bad. I may replace those after the rotors. Or I may just wait and do the whole front end, but that is a little more of a price commitment.

As EuroxS4 suggested, I checked the CV joints. The one on the right is nice and tight. That is where the sound seems to be coming from. I recently replace the outer joint on the drivers side with a Meyle CV joint from FCP Euro. That one seems to have a little play in it. I can't tell if it is in the joint itself or between the joint and the splines on the axle. But I did some tight turns in a parking lot and nothing is clicking. I was actually wondering if I've got a problem in the transmission where the inboard CV joint slides onto the output shaft.

I haven't tried to record the rattle. Maybe if rotors and sway bar links don't fix the problem, I'll try to record the sound.

Thanks again for the suggestions!

[Gin+]

My winter rat b7 has a bad ball joint and junk rotors. It's clunk city when lightly applying the brakes.