What causes brakes to pulsate right after rotor and pad replacement?

Question

I have a 2002 Infiniti Q45. I replaced the front rotors and pads on Sunday. It was the first time I've done this on a car, though I have done it countless times on various motorcycles.

I was careful to apply proper torque to all fittings and verified everything was clear before installing the wheels and driving the car.

The car drove fine all week and then today the brakes started pulsating and making a sound at the same moment of the pulse at 20 mph. At 30 mph, the pulsating and sound become scary, so I parked the car, put it up on jack stands, removed the wheels, and after inspection I can find nothing obviously wrong. I did notice that the right rotor has some visible scratches on it, but I can't see anything that could touch the rotor except the pads.

The pulsating is perfectly rhythmic, so I'm fairly certain that whatever is causing the pulsating is also spinning.

The rotors and pads are from Autozone.

Answer 1

Paul, I'd like you to open up those brakes again and examine the rotors very carefully. I just finished a conversation with a fella who described symptoms identical to yours. I walked him through a range of troubleshooting steps until finally I was nearly convinced that he had a cracked CV joint boot and he needed to replace an axle shaft when he suddenly found a fine hairline crack on one of his rotors. It was nearly undetectable, but he replaced the rotor and all is now fine again.

EDIT: BTW... what brand brake pads did you use? Some manufacturers recommend AGAINST any bed-in or burnishing procedure.

Answer 2

I've done countless brake jobs at the shop I worked at; without hearing/seeing the car here are some things that can cause noise/pulsating:

• Non-burnished brakes - like others have stated after putting fresh pads and rotors on a car you need to 'break them in.' I worked in a shop for a while and we didn't always do everything by the book, but when putting new pads and rotors on a car we would take some sandpaper to the pads and rotors, we'd call it 'roughing them up.' Then I would take the car for a test drive for a little and speed up to 20-30 mph and then hit the brakes with 'more than typical' force for about 10-20 times, depending on how much of a rush I was in.

• Knocked off a wheel weight when taking off the tire; it happens. I would suspect this would be the case if the pulsating feeling only happens at certain speeds and not at others, but it would not explain any loud noises.

• Something got caught up inside the wheel. I have had this happen on my own vehicle. A stick or rock gets caught in the right spot and it sounds like my car is SCREAMING something metallic and scratchy. Taking off the wheel and removing the object has fixed this in the past (also some erratic driving has as well other times).

• Imperfect / warped rotor - sometimes you can get a bad rotor. You can measure the rotors with a micrometer.

• Rotor not seated properly on hub. When you took off the old rotor did you take a wire brush to the hub to make sure to remove any debris/rust so that the new rotor(s) sit nice and flush on the hub?

• It's not your new brakes, it's your rear or something else like a hub, bearing or cv joint (I would think it was any of those three since they often make noise at all speeds).

Also, remember that just because you just did your brakes, it does not 100% mean that this is a brake related issue. I've patched tires on cars and had the customer complain because "as soon as he got home" his water pump went so it must have been something I did...sometimes it is just coincidental (but in this case it does sound repair related).

Answer 3

The Myth (Or, how to blame customers for bad brake jobs, since the problems usually take a while to show up)

What is passed off as a "warped rotor", and blamed on the user running through a puddle after heating the brakes, is a myth.

The shimmy feeling that comes from brakes is usually due to uneven friction material build-up on the rotor. This transfer from pad to rotor is supposed to happen, indeed it makes the brakes work better, which is why brakes function better after break-in. However when it happens unevenly, it produces a shaking or shimmy feeling. Why does it build up unevenly?

There are four major reasons for uneven friction buildup on rotors:

1. Rotors were of uneven thickness when new. Build-up occurs on the thick spots.

2. Rotors were eccentric when new or as installed. Build-up occurs on the high spots.

3. Uneven pad engagement. Pads installed not parallel to the rotor, or engaging unevenly due to rough unlubricated surfaces.

4. Improper break-in (a.k.a. "bedding"). Typically this involves heating the brakes up, then coming to a hard stop and leaving the brakes on hard. This puts a "pad imprint" on one part of the rotor, that will continue to catch more pad material and build up.

In all cases, it is the uneven friction as the rotor turns that causes the shimmy feeling, not a "warped rotor".

Since learning all this, I do the following and have eliminated all brake shimmy in my personal fleet.

Preventing brake shimmy

1. Checking all rotor's width at 8 spots round the disc with a micrometer. Thickness eccentricity should be zero, must be under .0015".

2. Check all installs with a dial indicator for runout. Spin the rotor with indicator at 90 degrees on the rotor face near the outer edge. Runout should be zero, must be under .004", the less the better.

3. Clean pad back, piston, and caliper. Replace shims. Proper and complete lubrication of all metal-to-metal contact points. I use Sil-Glyde, but there are other purpose made lubricants that will work. This allows pads to slide instead of tilt, and gives even contact pressure across the pad.

4. During break-in, avoid leaving the hydraulic brakes on after a hard stop on heated brakes. Coast, use the handbrake for the final stop, whatever it takes. (It is the front rotors that do all the work and heat the most).

Don't take my word for it, listen to the expert, here: http://www.stoptech.com/technical-support/technical-white-papers/-warped-brake-disc-and-other-myths

Answer 4

More than likely you didn't bed your brakes correctly. If you read this from Centric Parts, you find out exactly what I'm talking about. The specific part I'm talking about is the portion on an even transfer layer:

Note the emphasis on the word even, as uneven pad deposits on the rotor face are the number one, and almost exclusive cause of brake judder or vibration.

Improper bedding of your brakes after replacement can cause the issues you are talking about.

To fix this, you'll need to take your rotors back off and have them re-burnished. I believe you can reuse the brake pads, just ensure you go through the bedding sequence properly this time and it should solve your issues. Here is another thread which we talked about the proper bedding of brakes. Ensure you read my entire post, as there is an addition about bedding I place in an edit.

Answer 5

This symptom is a classic for lug nuts coming lose while you are driving. When lug nuts come lose the wheel will vibrate and after a time, as other lugs on that wheel come lose, it will scare you to death. Check all the wheels for lose lugs as it is hard to identify the correct rim with the lose lugs.

Sadly, I know this by experience.

Answer 6

I can't say for sure without a photo but in many cases it is rust on the hub. Many rotors have an extra hole machined in the rotor. It is usually located between two of the stud holes. I am not sure of why it is there, perhaps to help balance the rotor or to aid in the machining process. What can occur is that a small amount of rust will form on the hub flange. If the rust is not removed or the new rotor is mounted on the rust spot (the extra hole in the new rotor is not exposing the rust spot) the rotor will not sit flat on the hub. When the lug nuts are tightened the rotor will twist, resulting in pedal pulsation. You may luck out and be able to shift the rotor to expose the rust or just remove the rust and cure the problem.

Answer 7

Brake pad and discs are a well practised bread and butter job. Your problem can only be because of: Wrong or defective parts, incorrect fitting damage such as not using a caliper piston retraction tool, incorrect re-assembly of shims and bolts and anti-rattle springs, previous damage or mis-alignment being masked by the old pad wear, a foreign body introduced into the system. Avoiding harsh braking for a couple of hundred miles is all that is required to bed in a set of pads. Quite a few replacement brake components today come with bedding in compounds already applied and they should be used as out of the box. Avoid or dismiss all the guff you hear otherwise.

Answer 8

I don't know if you ever figured out what the problem was, but I will tell you my story. I have a 2003 Ford Ranger 2wd. I had a pulsating brake problem in my front disk brakes for 10 years until I finally figured out the problem. I bought the truck new and the problem started within the first 5K - 10K miles. In trying to fix the pulsation & wheel wobble, I replaced the disks 3 times each time with new bearings, seals, and pads. I bleed all 4 brakes multiple times. I checked the parking brake, rear brake, and the ABS. The ABS can be disconnected to simply check if this is the problem. I checked the lug torque, and properly bedded the pads on 2 different pad types (ceramic and semi-metallic). I also checked the front suspension and steering. NONE of this fixed the problem. And no matter how many times I was told the rotors were WARPED, or I was doing something wrong by some expert, nothing fixed the problem including replacing the rotors.

In trying to fix the issue again in 2011, I replaced only the brake pads with semi-metallic's as all the previous pads I tried were ceramic (I was still on my second new set of rotors). I decided to grease the caliper slide pins with caliper lube. The pins were well greased and slid nicely when I was done. SO, fast forward to a couple of days and the problem came back. I didn't think anything of it until I decided to replace the rotors and pads again for the third time a year later. After replacing the pads and rotor on the passenger side, I was just about done with the driver's side when by chance, I happened to check the caliper slide pins before installing the brake pads. I figured I did not need to bother with them as I had just greased them a year prior. To my surprise, the upper pin would NOT MOVE... The lower pin slid out no problem, but the upper took quite a bit of force to remove. (I think I used some pliers). In looking at the two pins, the only discernible difference was the rubber collar (or boot) that sat in a wide groove in the upper pin. I then looked at the pad and noticed that the pad was worn uneven.... It all started to come together!

According to the manual, a special lube was used on the caliper slide pins. They recommend not to remove it as there was no replacement for the grease at the time, but I think it's just a good silicone based grease. Regardless, I tried using silicone grease, and even making a new rubber collar to put in. I finally decided to just remove the STUPID RUBBER COLLAR! I was going to go down to the local Autozone and pick up a new set of slide pins and use the same solid pin without the groove for both the upper and lower. But I realized this was not necessary. The groove in the pin is well within the slide housing. The shear plane of the pin is at the largest diameter for both pins. Removing the boot will have no effect on strength or safety. In fact, I believe the boot is simply for noise and vibration abatement (isn't that ironic). BTW, for those who are going to say removing the boot is unsafe, please tell me how. I happen to be a Mechanical Engineer, so feel free to get technical.

So, I realized, my vehicle probably had very little lube from the factory, or moisture intruded into the caliper slide pin housing and caused the rubber collar to swell (or both). When you first drive the vehicle, everything is cold, but as soon as heat is pumped through the brakes, everything expands making the problem worse. The swelling causes the pin to seize on that side of the caliper causing the pad to apply uneven pressure, which in turn causes the pulsation. When I finally decided to apply some caliper slide grease the first time, this made the problem even worse as the as the rubber collar requires a grease that will not cause it to swell. It wasn't until my last go around with the pads and rotors that I discovered this and removed the rubber collar from the slide pins, one on each side. I have had not an issue since then in three years. I love driving my truck without pulsating brakes!

I can't tell you if this is the problem on your vehicle because you may not have the rubber collar. If not, then the best this will do is make you check the slide pins. But if you do have the rubber collar, I highly recommend you check this as it is very simple and inexpensive to fix. And you can check it by removing the rubber collar and trying for no cost. It just so happens that I also have an Infiniti I35. In replacing my brake pads last time around, I decided to grease the caliper slide pins on it. One of the pins on each side also had this damn rubber collar! Although I never had an issue with the brakes on the Infiniti, I canned the collar anyway. Have never had a problem with the I35 either.

Good luck.

Answer 9

so im leaning toward either an "about" to be bad wheel bearing/bushing, or you didn't scrub the rotors after during replacement. the anti-rust coating that come on them has been heard to cause these kind of issues.

Answer 10

My brakes pulsated and cruise worked some times on 95 Silverado replaced brake power booster fixed pulsating replaced brake light switch at brake pedal this fixed cruise control

Answer 11

Someone probably didn't do a proper run out test before they put it all together after the new rotors. Lateral run out test is needed when putting new rotors on a vehicle because the new face of the rotor doesn't hardly match the face of the old hub, or new hub either for that matter because of manufacturing. (Manufacturing tolerances and such) Always check the lateral run out, you can do it by eye. It's pretty easy to see the "wobble" if you have some kind of stationary object near the end of the disk. (Hold the disk on with a couple lugnuts and hand tighten the bolts for the caliper bracket without the caliper, this is useful here) it's a bit of a process but it will work. A dial micrometer on a magnetic base works best. Anything from 0.0 to .100 is ideal, .250 would be not so good on just about any application.