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Is it time for new brake pads and rotors?

Mr. Maboomba

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I am feeling a vibration from my rear brakes under moderate to heavy brake application. At the last track day under heavy braking the rear end felt like it pulled to one side, which was fun. My guess is pad deposits, since I've read the Brembo rotors on the GT350 are pretty immune to warping. I've also read that these rotors can't be resurfaced, so I was thinking it's probably time to replace them. New OEM pads and rotors are $1,850 so I want to be sure of my options before I pull the trigger.

Here are the measurements on my pads and rotors right now:

Driver Front - Pad: 8.2 mm to backing, 4.1 mm to wear bar. Rotor: 35.6 mm vs 34 mm minimum
Passenger Front - Pad: 5.6 mm to backing, 3.8 mm to wear bar. Rotor: 35.5 mm vs 34 mm minimum
Driver Rear - Pad: ?? mm to backing, 5.4 mm to wear bar. Rotor: 25.8 mm vs 24 mm minimum
Passenger Rear - 7.7 mm to backing, 4.6 mm to wear bar. Rotor: 25.8 mm vs 24 mm minimum

No cracking:

IMG_3976.jpg

IMG_3980.jpg
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pilotgore

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I am feeling a vibration from my rear brakes under moderate to heavy brake application. At the last track day under heavy braking the rear end felt like it pulled to one side, which was fun. My guess is pad deposits, since I've read the Brembo rotors on the GT350 are pretty immune to warping. I've also read that these rotors can't be resurfaced, so I was thinking it's probably time to replace them. New OEM pads and rotors are $1,850 so I want to be sure of my options before I pull the trigger.

Here are the measurements on my pads and rotors right now:

Driver Front - Pad: 8.2 mm to backing, 4.1 mm to wear bar. Rotor: 35.6 mm vs 34 mm minimum
Passenger Front - Pad: 5.6 mm to backing, 3.8 mm to wear bar. Rotor: 35.5 mm vs 34 mm minimum
Driver Rear - Pad: ?? mm to backing, 5.4 mm to wear bar. Rotor: 25.8 mm vs 24 mm minimum
Passenger Rear - 7.7 mm to backing, 4.6 mm to wear bar. Rotor: 25.8 mm vs 24 mm minimum

No cracking:

IMG_3976.jpg

IMG_3980.jpg
You have tons of pad left so I wouldn’t replace those just yet (although getting another set on order and having them sitting on the shelf is a wise idea.). About a year ago I adopted the rule of thumb that Kevin, @honeybadger , uses for brake pads. Dont start a track weekend unless you have 4mm or more of pad. While that doesn’t sound like a ton, so far I’ve always come away from 5+ hrs of track time over two days with at least 1-2mm of pad left. I always replace the pads if I’m below 2mm at the time of measurement.

I’ve warped two sets of factory front rotors before the heat cracking had reached the edge of the rotor, and having them turned at O’reilys for $20 each (or whatever it was,) was an absolute godsend. My left side gets significantly more heat from all the right turns and was always significantly worse than the right rotor. Don’t be afraid to give that a try.

Were you setting your parking brake after sessions? I’m just curious as I’ve never heard someone complain of rear rotors warping in a 350. In fact, I went through 3 sets of front rotors before it was time to replace the rears (after 9,500 miles, ~30 track days,) and only because the heat cracks were nearing the edge.

Just curious, what makes you suspect the vibration was coming from the rear and not the front? Do you recall which way the car felt it was pulling and can you duplicate it on the street? Rear end dancing on track under heaving braking can be common if you’re into abs or threshold braking.

If I were going to troubleshoot, I’d probably go in this order, which just so happens to be from least to most effort.
- Pull all the pads and inspect for condition. I’ve seen pad material crack and break off after it was wet, then sat in contact with a rotor. If nothing looks amiss, reinstall.
-Have the front rotors turned. They’re easy to remove compared to the rears, and the cost is minimal considering these are by far more likely to warp from heat compared to the rears.
- Have the rear rotors turned
- If none of that works, buy new pads and rotors and keep the old as spares.

Best of luck.
 
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Mr. Maboomba

Mr. Maboomba

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You have tons of pad left so I wouldn’t replace those just yet (although getting another set on order and having them sitting on the shelf is a wise idea.). About a year ago I adopted the rule of thumb that Kevin, @honeybadger , uses for brake pads. Dont start a track weekend unless you have 4mm or more of pad. While that doesn’t sound like a ton, so far I’ve always come away from 5+ hrs of track time over two days with at least 1-2mm of pad left. I always replace the pads if I’m below 2mm at the time of measurement.
Are you measuring to the backing plate or to the wear tab? I can't imagine it's much fun to drive the car around with the wear tab rubbing on the rotor squeaking like hell.

My pads have about 3K miles and 5 track days on them. My rotors have 7K miles and 13 track days on them.

Were you setting your parking brake after sessions? I’m just curious as I’ve never heard someone complain of rear rotors warping in a 350.
Never for more than a moment, the amount of time it takes me to jump out and chock my wheels.

Just curious, what makes you suspect the vibration was coming from the rear and not the front?
I can feel the vibration in my seat but not through the wheel.
 

pilotgore

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Are you measuring to the backing plate or to the wear tab? I can't imagine it's much fun to drive the car around with the wear tab rubbing on the rotor squeaking like hell.

My pads have about 3K miles and 5 track days on them. My rotors have 7K miles and 13 track days on them.



Never for more than a moment, the amount of time it takes me to jump out and chock my wheels.



I can feel the vibration in my seat but not through the wheel.
Im measuring to the backing plate. My gloc pads don’t have squeakers, and with a pair of needle nose plyers you can be a cool kid too :)

You may want to consider not using the parking brake at the track. When you set the parking brake after a session, you’re making contact with the rotor. Unless you roll after releasing the parking brake, the pads remain in contact with the rotors (which obviously isn’t a good thing.) Personally, I get into my spot, shut the car off, roll slightly and slowly release the clutch in gear.
 

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I had recently developed a warble under medium pressure braking. I had also installed sways, springs, and apex wheels with spacers, so I wanted to be 100% confident it was brakes and not one of the other components. I bought new front rotors from Ford White Bear Lake for $217 each (they're the pre-2019 with drilled holes). My pulsing is totally gone. I had previously come straight to park. At my most recent event I drove around until under 220F, then parked it in gear and didn't apply brakes.

Not saying causes are similar, just my experience.
 

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honeybadger

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I had pulsations on my first set of brake rotors due to using the parking brake. Drove me mad before I found it. Didnlt even think to check the rear rotors since I didn't remember hitting the rear brake - but then I found it up once at the track and realized my buddy had done it.

Similarly to @pilotgore - I run my brake pads much further than your pictures. But I ALWAYS carry an extra set. I've seen pads go from "going to need new ones soon" to "whoops" in 2 sessions. I've also gotten an entire weekend out of them. YMMV
 
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Mr. Maboomba

Mr. Maboomba

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Using the parking brake when your rotors are hot is such a rookie error, which is why I would always do it for just a second and then let my car roll forward a bit onto the chocks. I will start exclusively turning it off in gear, chocking it, and then turning it back on to idle and cool down.

Can you see brake pad deposits on the rotors?
 

pilotgore

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Using the parking brake when your rotors are hot is such a rookie error, which is why I would always do it for just a second and then let my car roll forward a bit onto the chocks. I will start exclusively turning it off in gear, chocking it, and then turning it back on to idle and cool down.

Can you see brake pad deposits on the rotors?
In my experience, yes. Typically you can see an outline of the pad. It’s also totally possible setting the parking brake even temporarily rapidly cooled a small section of the rotor, which led to warping. There may be no visual indication.
 
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Mr. Maboomba

Mr. Maboomba

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I confirmed the brake pad measurements today (they're all fine - 6.6-8.3mm) and checked out the rotors. They look OK to me - I do see some light deposits but nothing I can actually feel, nothing that seems like it would cause problems. You can see photos at https://photos.app.goo.gl/siLKMapL8WV4YcST7.

I took the car out for a test drive and reminded myself of what happens on the street - it's not a vibration so much as inconsistent declaration in response to consistent brake pressure. After seeing a video, my mechanic says it's probably tire shine, grease, deposits or warped rotors.
 

JAJ

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Im measuring to the backing plate. My gloc pads don’t have squeakers, and with a pair of needle nose plyers you can be a cool kid too :)

You may want to consider not using the parking brake at the track. When you set the parking brake after a session, you’re making contact with the rotor. Unless you roll after releasing the parking brake, the pads remain in contact with the rotors (which obviously isn’t a good thing.) Personally, I get into my spot, shut the car off, roll slightly and slowly release the clutch in gear.
The GT350 parking brake is a rear drum brake inside the rotor hat. That's how FP put 4 piston top loader rear calipers on the GT350. The slider-brake caliper pad deposit thing doesn't happen.

For the OP, your rotors look fine and the pad measurements look good too. If you're feeling vibration under heavy braking it's probably not the rear brakes.
 
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Mr. Maboomba

Mr. Maboomba

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Final update: I took the car to my mechanic for an inspection. He wasn’t 100% sure but his best guess is that I had some material on my right front rotor that was letting the pad slip when it went over that part of the rotor. At his advice I changed out the front pads and rotors. My braking issue is now gone.

CC899C88-8224-491C-B3B8-29713788EF01.jpeg


Not sure if I see what my mechanic did, but maybe one of you will.

6B5EDD97-0423-41B1-AAE5-477DE6979D67.jpeg

6D2E85E5-F89C-4608-9DFA-DBCFB32B28E1.jpeg


My front left rotor did have this suspicious discoloration on the inside.

E0D29A96-203F-472C-A4FF-75708CB2C397.jpeg
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