So I changed my worn out (front) stock pads to HPS pads a few weeks ago, and all was well. I finally got a chance to change the rotors today, and to make a long story short, I had to snap the heads off the torx bolts that retain the rotors in order to remove the rotors. I was concerned about operating the car without the bolt in place due to excess slack in the rotor assembly as a result of a loose tolerance between the lug bolts and the rotor, but the general consensus I got from the few people who answered my post was that it is OK to drive without the retention bolt. (see https://www.northamericanmotoring.co...d.php?t=157349 for more detail)

I couldn't find any conflicting information elsewhere, so I took the car out to bed the pads. About 10 stops into the process, a soft, rhythmic thunking from the driver's side wheel area became apparent during moderate braking. There is no pulsation in the pedal, and the car stops smoothly. Everything is in place and tight, and the rotors show no signs of movement (I marked them) despite not having the retention bolt in. I can't detect anything abnormal or out of place, and yet the thunking won't go away.

Useful info:

2005 MCS, 40k miles.
Pads: Hawk HPS, with roughly 200 miles on them
Rotors: Brembo OE-style replacement rotors

 

check the spring clip on the outside pad, may be off or gone.

This retaining wire/spring clip


Also check the two bolts holding the dog bone to the hub and the two bolts holding the caliper to the dog bone. The bushings may also be going bad.

 

I can't imagine the torx would be the issue - especially if it's rhythmic.
It'd start by jacking the car up and spinning each wheel to see if you can isolate the source. Perhaps a bit of pad material fused to a rotor??

 

I checked again this morning in better light - everything is tight and in place as it should be. A quick trip down the road revealed the same thunking.

My local MINI service dept. suggested that it could be the heat shield banging against the rotor after having been tweaked during rotor installation... To me, the sound is a bit dull to be a heat-shield related noise, but the SA says he gets the complaint a lot that's what it is 99% of the time.

 

My brakes were rubbing the backing plates and it did not sound like you describe, it sounded 2 pieces of metal rubbing together more like scraping noise.

 

Check the control arm bushing. (the rear mount for the front control arms) If the bushing has gone bad the control arm could be contacting the mount.

 

I've got aftermarket rotors and pads: TSW rotors and Bobcat pads I purchased from AutoXCooper.com.
I still get a thunking sound that goes away when I apply the brakes even slightly. Numerous times I've had the rear calipers off to inspect the inboard pad... they had popped off the piston head and I had to snap them back on. This past weekend they still appeared to be in place. It's defintiely the rear set as when I apply the parking brake while driving the sound vanishes.
One thing I notice is that with the pads/dogbone removed, the rotor spins freely. With everything together the rotor does not spin freely. Pretty restricted.
Do the rear caliper pistons need to be manually rotated in with the (Harbor Freight) piston compression tool? I would think they would retract off the rotor surface by the natural braking action. Learning...

 

Dave the rear pads only need to be "manually rotated in" when you are changing the pads. Once you set the parking break or apply the break pedal they should adjust to the correct clearance and float there.
Z06C5R only did his fronts. That is when his problem started.

 

The sound isn't much like I would imagine it would be if the heat shield is somehow in play - it's a very dull "thunk", similar to hitting your palm against a desk or something like that... Based on the sound alone, I would sooner suspect the control arm bushing or something like that. But why would that suddenly spring up after a brake change? And would it really go out at only 40k miles on completely stock suspension?

 

Did you clean the surface of the rotor that sits against the hub? Did you clean the mating surface of the hub also? It doesn't take much crud or rust on this surface to prevent the rotor from sitting perfectly flat against the hub. It would be easy to have a little burr left over from when you had extract that torx bolt, that could cause things to not sit flat also...

You want these surfaces to be good-n-clean but also free from any oil or grease.

Jason

 

Yeah, I sanded them down pretty good to take off the rust and crud that was on there. Wouldn't that come through the pedal as a pulsation though, since it would essentially be a crooked rotor?

 

I'm leaning toward a suspension issue. The pads usually back off themselves when you release the pedal in a moving car.

I'm wondering if something gave way when you were braking hard, bedding in the pads?

 

From my experience, no pedal pulsation. My guess is the floating caliper just follows the rotor, but the thickness of the rotor does not change therefore not forcing any fluid back to feel in the pedal.


Just my experience.

Jason

 

If the rotor is out of true or shaped like a potato chip you will feel a pulsation in the brake peddle. If the rotor is out of true you would have felt the pulsation before & after you replaced the brakes.

 

Eric's diagnosis has merit based on my own experience. I changed over to Carbotech Bobcats and PowerSlot rotors this past summer, and shortly after bedding I started to notice a knocking/tapping noise coming from the left front wheel during braking. Its frequency was a function of my speed and the noise was louder under heavy braking. It almost sounded as if one of the pad backing plates was rocking back and forth against the caliper.

I was bemoaning my switch to slotted rotors and after a few weeks was ready to take the assembly apart and try applying more caliper grease when I began to notice that the noise wasn't there anymore. I've motored for 4+ months since and have not heard a single knock. I inspected the pad assembly and it is still properly aligned, not wedged or caught abnormally.

I ended up concluding that there must have been something along the rotor surface (pad material?) that was causing uneven friction, maybe a result of inadequate bedding. Once I worked my way past it, the brakes have functioned perfectly and quietly.

 

On an Audi I used to own, the aftermarket pad did not fit tight on the piston side and would make a thunking sound over bumps when the brakes were not applied. Simply spreading the 3 spring tongs (whatever they are called) so that it fit more tightly into the piston got rid of the sounds

Just a possibility; remember floating caliper brakes like ours work by having the pads oh-so-slightly in contact with the rotor but not really snug against until pedal pressure is applied; it's amazing how tiny noises get amplified and telegraphed through mechanical bits of a car.

Good luck hunting

 

So it ended up being the tie-rod ball joint - seems it's suddenly gone all slack. Woohoo! To the dealer!

 

Wow - never would have guessed that one. Let us know if that solves the problem. Can't see a loose ball joint causing rhythmic thumping.

 

The wheel wobbles under moderate brake pressure and causes the steering knuckle to knock around on the loose joint. It is kind of a stretch, but that's the only thing down there making noise.

 

I get the 'pad material stuck on the rotor' problem every time I go to the track. It usually takes 25-50 miles of normal street driving to shave everything off and get the 'click, click, click' pedal feel to go back to a norma, smooth feel.

Congrats on a solid diagnosis. Good luck on the fix.