Just replaced front pads/rotors, hearing a "thud" when braking
 

Hey guys, I'm stumped. I replaced my front pads and rotors with r1 concept rotors and Hawk HPS pads. It now sounds like there's a dull "thud" when I initially hit the brake pedal on the driver side. I couldn't tell if it's coming from the master cylinder or the pads/rotor... any idea what this could be? It kind of sounds like the pads aren't in contact with the rotor and the initial brake pressure is "slapping" them against the rotor.

I'm aiming to do my rears today to but I'd definitely like to get this finished first.

It doesn't do it at a standstill, I can pump the brakes all I want while not moving and it doesn't do anything, and it doesn't seem to start doing it until I back out of my driveway, like it needs a bit of rotation before it starts happening.

It's either that or you don't have the caliper bolts tight enough and the caliper is moving slightly. Have you driven it around the block a few times? It could also be that the pistons need to settle in to position after you pushed them in for the new rotors.

Turns out I'm an idiot. I had loosened the caliper bolts on the first side I did to be able to get the pads in and never re-tightened them. They were nearly a half inch out :eyebulge:

:stupid:

Rears done and now everything feels great! They're a little loud at the moment, I can hear them (not squeaking, just working) and assume they'll settle in, and I can't hear them with the windows up anyways.

Thanks R1!

Did you do the pad bedding-in recommended by the pad manufacturer? When I changed the pads and Rotors on my HHR they included a procedure for bedding-in them.
Here is an example from Tirerack.com

All brake pads must be bedded-in with the rotor they will be used against to maximize brake performance. The bedding-in process involves a gradual build up of heat in the rotors and pad compound. This process will lay down a thin layer of transfer film on to the rotor surface. Following the bed-in procedures provided by the manufacturer will assure a smooth, even layer of transfer film on the rotor and will minimize brake judder. Here are a few things to keep in mind when installing new rotors and pads:

When installing new pads, the rotors should be new or at least resurfaced to remove any transfer film from the previous set of brake pads.

It is critical that the installer clean any rust, scale, or debris from the hub mounting surface thoroughly and check it for excessive run-out with a dial indicator gauge before installing the rotor.

The new rotor should also be checked for excessive run-out using a dial indicator gauge before the caliper and pads are installed. If a rotor has excessive run-out of over .004" (.10mm) it should be replaced.

If your new rotor has excessive run-out, please contact our customer service department for a replacement rotor. Do not install and drive using the rotor! Rotor manufacturers will not warranty a used rotor for excessive run-out. Running with excessive run-out on the hub or rotor will cause vibration issues.

Failure to follow these procedures may result in brake judder, excessive noise, or other difficulties in bedding-in the new brake pads. The pads need a fresh surface to lay down an even transfer film. Residue from the previous pad compound on the surface or an irregular surface on a used rotor will cause the pads to grip-slip-grip-slip as they pass over the rotor surface under pressure. The resulting vibration will cause noise and telegraph vibrations through the suspension and steering wheel. This vibration is known as brake judder or brake shimmy. This is typically caused by an uneven transfer film on the rotor surface or an uneven surface on the rotor not allowing that transfer film to develop evenly. This is often misdiagnosed as a warped rotor.

Bedding-in new pads and rotors should be done carefully and slowly. Rapid heat build up in the brake system can lead to warped rotors and or glazed brake pads. Most brake pad compounds will take up to 300-400 miles to fully develop an even transfer film on the rotors. Following are the recommended bed-in procedures from each manufacturer:

AKEBONO

400 to 500 miles of moderate driving is recommended. Consumer should avoid heavy braking during this period.

ATE

400 to 500 miles of moderate driving is recommended. Consumer should avoid heavy braking during this period.

BREMBO Gran Turismob

In a safe area, apply brakes moderately from 60mph to 30mph and then drive approximately 1/2 mile to allow the brakes to cool. Repeat this procedure approximately 30 times.

HAWK

After installing new pads make 6 to 10 stops from approximately 35 mph with moderate pressure. Make an additional two to three hard stops from approximately 40 to 45 mph. Do not allow the vehicle to come to a complete stop.When completed with this process, park the vehicle and allow the brakes to cool completely before driving on them again. Do not engage the parking brake until after this cooling process is compete.

NOTE: Hawk racing pads (Blue, Black, HT-10, HT-12) may require a different bed-in procedure. Contact your sales specialists at the Tire Rack for racing application information.

POWER SLOT

Follow the brake pad manufacturer's recommended break-in procedure taking care not to produce excessive heat in the system. Avoid heavy braking for the first 400-500 miles.

Glad you found the problem! :thumb:

If I read the manual correctly if you loosen the caliper bolts they are supposed to be replaced.

That is true. I've had mine off and back on a couple times and never knew that until I read it somewhere! :doh: I'm replacing them this winter when I do some brake work!

I plan on ordering several sets of bolts so i always have new ones around. Especially on track days in case i run into trouble.

Well now I'm hearing something completely different. The initial whine is gone, but now I have a rotational noise... The best I can describe it is that it sounds like a ratchet. The rotors are slotted/dimpled, is this something to expect from this setup? I can't imagine its normal because as far as I can tell its only happening on the front right. When I get up to speed it doesn't go away but it's less noticable as the sound speeds up.

Jack each wheel off the ground one by one and turn them by hand. If something is out of whack, loose, misaligned, etc., you should hear it...Did you clean everthing good between the rotors and the hub? and put back in the torx screw?

I put on R1 rotors and hp plus pads myself, broke them in just like it says on the box, and have had no issues other than the expected squeaking when coming to a slow stop...

Does it happen at slow speeds or do you have to get above a certain speed?

Is it possible you damaged the rotor, caliper or pads when you had the bolts loose?

Yikes, I hope not!

Its only noticeable at low speeds, and only when there's something near me for the sound to bounce off of (high curb, fence, etc). I'll get it up in the air when I get home and see if I can pinpoint it by turning it manually. The caliper, rotor, and pads all look fine as is and its performing just fine.

Edit: It also becomes far less noticable when braking. The harder I brake, the less it sounds. Maybe the back side of the rotor is cracked.... :(

I have a clicking noise with my slotted DBA 4000 rotors.

According to the dealer master tech (he did the Tech II ABS bleed procedure for me) this is normal for slotted rotors.

I did a few web searches which confirm it as well. Start typing in "slotted rotors noise" into Google and notice the search options it gives you. Apparently people have asked this question before.