Weird grinding when pressing brake

[DickR]

What the F 'n F! I put the 20" American Muscle Performance Package Replica wheels back on and the damn grind/humming comes back! I'm at a loss of ideas on what is causing it. I know the wheels in general are a little heavier than the stock 19" wheels are, but not to the extent that they will make a grind noise when breaking at low speeds. Once I switched back to the stock wheels, the noise completely went away.

First, did you remove the "sheet metal" fastener on the lugs (one or two per rotor)? Unless the new wheels have recesses like the oem wheels they won't seat properly on the rotor hub face.

Heavier shouldn't make any difference.

Front only or both ends?

Both sides? Since you checked for brake caliper rubbing on the wheel(s) what about tire rubbing on something due to offset change, if any, since the wheels and tires are both wider.

Have you done any mods that might have left something loose?

Have you verified that the wheel bore is large enough to clear the wheel bearing hub?

Straight line braking or when turning and braking?

Gentle versus heavy braking?

ALSO: What brand and size tires? And have you tried just changing the fronts or the rears to isolate which end of the car?

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[Jeff_oddo]

First, did you remove the "sheet metal" fastener on the lugs (one or two per rotor)? Unless the new wheels have recesses like the oem wheels they won't seat properly on the rotor hub face. New wheels have same recess on them so the lugs fit perfect

Heavier shouldn't make any difference.

Front only or both ends?just front wheels

Both sides? Since you checked for brake caliper rubbing on the wheel(s) what about tire rubbing on something due to offset change, if any, since the wheels and tires are both wider.yes both sides make the slight grind/humming noise at 30mph and slower, no other time.

Have you done any mods that might have left something loose?nope

Have you verified that the wheel bore is large enough to clear the wheel bearing hub?yes. They are direct replica wheels as the actual performance package wheels except they are in a 20" size, and the mustang even comes in a 20" wheel. They are the 20x8.5 front and 20x10 rear.

Straight line braking or when turning and braking?so far straight line braking

Gentle versus heavy braking?you can hear/feel it more when coming to a complete stop, no other times at higher speeds.

ALSO: What brand and size tires? And have you tried just changing the fronts or the rears to isolate which end of the car?tires are Nitto NT555 255/35/20 front and 275/35/20 Rear. Haven't swapped front for rear yet...

 

[DickR]

Hmmm (sorry bad pun).

Do you have to be braking or do you have the noise/hum just from driving slowly?

If it does it with no braking my guess is the tread pattern of the tires is the source of the noise. I had a set of Dunlop ZII's last year on my 2012 that made a loud whine at about 75 mph due to the tread pattern.

This assumes that the tires are rotating the correct direction :-) (that is they are mounted on the correct sides of the car per the tread pattern and the arrows that are probably on the sidewalls).

 

[Jeff_oddo]

Hmmm (sorry bad pun).

Do you have to be braking or do you have the noise/hum just from driving slowly?only when braking...

If it does it with no braking my guess is the tread pattern of the tires is the source of the noise. I had a set of Dunlop ZII's last year on my 2012 that made a loud whine at about 75 mph due to the tread pattern. possibly... Maybe I need to put more miles on these tires and see if it truly is the tread pattern.

This assumes that the tires are rotating the correct direction :-) (that is they are mounted on the correct sides of the car per the tread pattern and the arrows that are probably on the sidewalls).

they are correctly installed. Lol

 

[DickR]

In that case try them backwards to see if it makes a difference? If it is the tread pattern backwards has a good chance of at least sounding different.

 

[Jeff_oddo]

Still confused what might be causing it. Drove it today and the noise only comes around 30mph and below. I hit the brakes at higher speeds and the noise isn't there.

 

[wmsky33]

Have you tried putting the front of the car up on jackstands and spinning the wheels by hand to see if you can hear anything? Maybe even get someone to sit in the car and lightly apply the brakes while you spin the wheels?

 

[Jeff_oddo]

Have you tried putting the front of the car up on jackstands and spinning the wheels by hand to see if you can hear anything? Maybe even get someone to sit in the car and lightly apply the brakes while you spin the wheels?

I'll try that. I'm also going to look into getting the TSB done on it due to the brake noise. Looks like they are replacing the rotors with a new part number

 

[DickR]

Jeff - Based on the info you've provided my guess is tire noise. Have you experimented with different pavement types such as concrete vs. asphalt?

FYI I autocross my 2015 GT PP and have one set of Bridgestone RE-71R's that were very quiet when new but now that the tires have been subjected to 150 autocross runs and 6000 miles they have become noisy, especially when slowing to a stop. I realize your Nittos are brand new but even different models of tires frequently make different noises. That is one reason Tire Rack and other tire testers include noise evaluation in their data. Aggressive tread patterns like your Nittos have can be noisy, especially compared to an oem tire that needs to be very "civilized".

Google Tire Cavity Noise if you are interested.

Also, for what it is worth, my GT PP was built on December 18. Absolutely no brake noise the vast majority of the time. Any brief noise from the brakes is related to either damp/wet such as first use after being put away wet from washing or from driving in the rain. The brakes have been used hard and gotten "smell hot" in a test session autocross when new but not fully bedded yet from the previous gentle street use. No track use.

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