Rotor and pad bedding procedure/problem

[01sapphirebob]

Ok, so me and stretch finally got my rotors and pads installed and we went out to bed the pads and rotors. We came across an interesting noise/sound. When stepping on the brakes with moderate pressure there appears to be an almost knocking sound. Like you can hear the rotor "hitting" the pad. We got about 1/4 of the way through the factory bedding procudure and headed back to the house to check things out.

Everything seems to be in working order. All bolts were tightened to service manual specs. There doesnt appear to be any hangup in terms of a stuck piston. We picked the front of the car up and the wheels appear to spin freely except in one spot on both sides of the car (front) where it almost seems like the rotor is catching the pad. After a couple of phone calls we went back out to finish the bedding procedure but the car is still making the noise. There is NO vibration in the steering wheel when this is happening.

Any ideas/suggestions? One person we talked to suggested a more aggressive bedding procedure but ill take all the advice i can get.

The setup up front is OEM rotors (which had a zinc coating on them) and Hawk performance pads.

[Vipernoob]

I would make sure there is nothing between the rotor and the hub.

[FrankBarba]

How tight is the hub ?

[01sapphirebob]

How tight is the hub ?

What do you mean when you say "tight?" Do you mean does it spin easily or is the hib itself loose.

[mjorgensen]

Is there any visible irregularity's on the rotor surfaces such as a darker compound spot?

[01sapphirebob]

Is there any visible irregularity's on the rotor surfaces such as a darker compound spot?

Not that i noticed. When i get home today im gonna pull the wheels off and take another look. The rotors came from mopar and had a spray on zinc (i think) coating on them instead of the usual grease. Not shure if this is playjng a role or not.

http://www.jeepforum.com/forum/f310/...topics/1249959

I did a bit of searching online and came across this thread from a Jeep forum. In the video you hear a knocking/hitting sound. It seems to be exactly what im experiencing.

[LmeaViper]

Huh, looks like you will need to do some CSI investigation to find your solution.

Can you tell if it is one side or both sides of the car that you hear the knocking on?
Are the rotors sitting 100% flush with the hub?
Also is the rotor in question 100% concentric? Maybe that could be causing the knock as there isn't much room /tolerance in the braking system components.? Note I had a lower pulley on my Cobra back in the day that surprisingly wasn't fully concentric.

Can you take the rotor to a machine ship and get them to put it on the lathe and check it?
Any signs of wear or contact after driving for a while?
Are the pads loose in any way and twisting / turning slightly under braking account there is a rough section on a portion of the rotors?

[ViperPete]

When I replaced the calipers/rotors/pads on my srt10, I hear the pad "knock" all the time. The pads are shifting when brakes are applied. It's never caused any problems.

[01sapphirebob]

When I replaced the calipers/rotors/pads on my srt10, I hear the pad "knock" all the time. The pads are shifting when brakes are applied. It's never caused any problems.

Did it ever go away??

[Steve M]

When I replaced the calipers/rotors/pads on my srt10, I hear the pad "knock" all the time. The pads are shifting when brakes are applied. It's never caused any problems.

I had something similar on my daily driven truck...the pads would make a very audible clunk when going from forward to reverse (or vice versa). Smearing some anti-squeal grease on the backs of the pads cured this issue completely...it is just sticky enough to keep the pads in place (at least enough to keep them from moving around too much in the brackets).

[01sapphirebob]

I had something similar on my daily driven truck...the pads would make a very audible clunk when going from forward to reverse (or vice versa). Smearing some anti-squeal grease on the backs of the pads cured this issue completely...it is just sticky enough to keep the pads in place (at least enough to keep them from moving around too much in the brackets).

I did use the grease on the front pads. Perhaps not enough? I still have the packet and I would say its maybe half empty.

[Steve M]

I did use the grease on the front pads. Perhaps not enough? I still have the packet and I would say its maybe half empty.

It doesn't take much...just a light film is all that's required. Was it sticky at all? I don't remember what exactly I used (I'll have to see if I can dig up the package), but it was more sticky than greasy.

You could also have a different issue altogether.

[01sapphirebob]

It doesn't take much...just a light film is all that's required. Was it sticky at all? I don't remember what exactly I used (I'll have to see if I can dig up the package), but it was more sticky than greasy.

You could also have a different issue altogether.

I wouldn't say it was sticky. Greasy. More like a lubricant.

I'm hoping theres no major issue here. Some have said it could be as simple as a different sized pad which I will check on tomorrow as I did not go with the OEMs but with Hawks. I'am also not 100% sure I've worn off the coating that was on the rotors yet.

[ViperPete]

When I replaced the calipers/rotors/pads on my srt10, I hear the pad "knock" all the time. The pads are shifting when brakes are applied. It's never caused any problems.

Nope I hear it all the time.

I even hear it in our brand new Maxima.

[St.Char]

Did you go with the Semi-Metallic or Ceramic. It's possible you have a defective pad or rotor. It's also possible that the coating that came on the rotor has not completely been removed, this would be my first concern. I would inspect the rotor and make sure the surface is clean, you may need to use some brake cleaner on the surface. I would only do this after you have properly completed the bedding-in process..

[01sapphirebob]

I took some pictures of the setup so everyone could see what i'm working with...

Drivers side...








Now this picture interest me and is giving me some thought on a theory. Could the pads be shorter then the OEM's and thats whats causing them to shift? I say this because I'm starting to thing this may be the issue. Look at the pad on the left and see how much open space there is at the top of the pad. Not the pad material but the backing plate. This is again just a theory which i'm gonna try to test out later today.



Pass side...

[Steve-Indy]

Certainly looks like the slightly smaller new pad is allowing "play"...and, could be making the sound that you hear on braking.

Is that a small divot at the edge of the rotor? Worrisome!!

Great job with your photos, Bob.

[01sapphirebob]

Certainly looks like the slightly smaller new pad is allowing "play"...and, could be making the sound that you hear on braking.

Is that a small divot at the edge of the rotor? Worrisome!!

Great job with your photos, Bob.

I couldnt exactly tell/decide if it was a divit or not. Didn't really feel it on the surfaceof the rotor. I also think it was there before the rotor went on the car.

[01sapphirebob]

UPDATE...

Or lack there of. After a miss communication with my Tech I wasn't able to get my car in to see him on Tuesday so I will take it in the coming Monday.

[Angleiron]

So here is what I found regarding bedding zinc coated rotors. The noise you were probably hearing was the anitlock system maybe?

"If you just installed rotors with zinc plating or if the rotors have an anti-corrosion phosphate coating, you should postpone bedding until normal driving has allowed your pads to polish the rotors clean and removed all traces of the plating or coating. If your new brake rotors have an oily anti-corrosion coating, clean this off thoroughly with brake cleaning spray and/or hot soapy water before installation."

[01sapphirebob]

So here is what I found regarding bedding zinc coated rotors. The noise you were probably hearing was the anitlock system maybe?

"If you just installed rotors with zinc plating or if the rotors have an anti-corrosion phosphate coating, you should postpone bedding until normal driving has allowed your pads to polish the rotors clean and removed all traces of the plating or coating. If your new brake rotors have an oily anti-corrosion coating, clean this off thoroughly with brake cleaning spray and/or hot soapy water before installation."

Could be. I didnt feel any feedback in the pedal though. When the rotors came in i tried to donsome quick research on the coating and from what i read i could clean it off or leave it on. Nothing i saw was favoring one method or the other so i figured one less thing and let the pads clean the rotors off.

[Steve-Indy]

Am curious to know exactly how the degreased, coated rotor would combine with ABS system (which was not activated by pedal pressure) to create the described sound.

[01sapphirebob]

UPDATE/Resolution!!

SO I got the car into my tech this evening. He took the wheels off and checked the drivers side rotor as he determined that is where the knocking sound was coming from. He checked the rotor for run out and found it had a small bit of imperfection in it. He put it on a lathe and turned it a little bit. Took the car out for a road test and the knocking sound was gone!!! I even slammed on the brakes a few times on the way home just to make sure I wasn't dreaming.

So...Brand new rotor from MOPAR needed to be turned. Hopefully this thread will help people in the future should they encounter this problem.

[My98RT10]

Great news and glad you found the culprit! I do have a brand new set of OEM front rotors in my basement (manufactured in 1998). Will definitely get them checked before I install them. Thanks!

[Coloviper]

Glad you found it! It's a manufactured product, so it happens. Hey my 06' Cayenne Turbo S had the front rotors out of round on a brand new vehicle. Lots of Cayenne and Panamericas did with the big brake package. Caused vibrations and some pad knocks. Porsche would not replace because the brakes still worked safely. It is frustrating. I replaced them recently but after 30k miles on them, I am getting the clicks sound at slow speeds when applying the brakes. This thread was helpful as I think my front pads are moving around slightly. I have a ton of pad life left but you never know. As it has 118,000 miles on it, stuff happens. Thanks