Rotor Help

[Jamesmcga]

I have a 2020 GT 350 that I have now gone through three sets of rotors because of steering wheel shake during high-speed braking (150 to 60). The previous rotors were using stock brake pads so now on the 3rd set I purchased Ferodo Dsuno pads.

I bedded them with a good 20 or so stops on the street and just finished a track day at road Atlanta … this is what they look like. Is this normal for a trackpad? It seems like there are areas on the rotor that the pads are not making contact with.

Any suggestions?

The car spends 90% of the time at the track.

 

[TMSBOSS]

When you say you went through three sets of rotors, why did you swap them out? Cracks, warping, pulsing while stopping?
The reason I ask is because folks on FB (mostly) have complained that they “Crack” rotors when all they have is a little checking, minor lines which do Not go through the surface of the disc. If you are swapping out rotors when they check, send them to me, there is usually plenty of usable disc left. Lol.
I keep a spare set of rotors in my trailer in case a rotor actually cracks. Until then, I run them as long as wear is even and the rotor meets minimum thickness specs.
A problem I had when I started on track was pulsing, vibration when braking and sometimes while just driving after an event. The cause, not following pad manufactures bedding guidance as well as leaving the cooling ducts open while bedding. The idea of bedding is to get the pads and rotors hot so you have a good even transfer of brake material to the rotor. With the cooling ducts open, the pads and rotors would not get hot enough. Add some tape to the front of the ducts and then bedding fixed my problem. Pad build up which causes a pulse can be removed with a small DA sander, then re-bed.

 

[thelostotter]

Looks good to me. Some street driving on the way home will probably make them look a bit more uniform.

If your car is stopping how you expect and you aren't getting any shuddering then I wouldn't change a thing.

 

[Stan Whitney]

That actually looks good. I had the brake shudder on my 350 as well. Would come and go, even with new pad/rotor combo's. Worst was used rotors and new pads (same compound).

 

[Jamesmcga]

Thanks everyone. I’m gonna chalk it up to not following the correct bedding process for the first 2 sets. I may go back and try to sand them just so I don’t have to spend another $700 on rotors when the time comes. The new Dunso pads did perform well on the track yesterday at Road ATL.

I also do not have any brake cooling. Another thought I had was that the rotors are getting entirely too hot and are just warping when they start to cool down between sessions.

is that a possibility?

 

[TMSBOSS]

Possible, yes. Likely, I don’t think so. Hold onto the rotors you have and hit them with a DA sander. They should be ready to bed and use again.
Dont feel too bad. I thought I trashed a set of Girodisc rotors on my boss. I burned through a set of pads during a weekend at Road America. I even checked runout. Yea, run out on floating rotors Fortunately I don’t throw anything away.
The good news, you have spared. I looked for rotors on South Florida Fords site. Back ordered. A good time to have spares.

 

[JAJ]

Thanks everyone. I’m gonna chalk it up to not following the correct bedding process for the first 2 sets. I may go back and try to sand them just so I don’t have to spend another $700 on rotors when the time comes. The new Dunso pads did perform well on the track yesterday at Road ATL.

I also do not have any brake cooling. Another thought I had was that the rotors are getting entirely too hot and are just warping when they start to cool down between sessions.

is that a possibility?

It's hard to say if you have a bedding problem or not. Bedding does two things - it puts a "transfer layer" of pad material onto the surface of the disk. That happens regardless of when you do it - brand new pads will lay down a layer on the first hard laps. BUT, the second thing that bedding does is "cook" the pad material so it works better and lasts longer. That involves getting the pads really hot in a controlled way and letting them cool down completely. The "bedding instructions" you read combine both features into one operation. The reason I'm explaining this is that the rotors don't care about cooking the pad material - they just need the transfer layer on them and they're happy.

From what you've said and written, I don't think you have a bedding problem. Your problem with the factory pads sounds like you might have had the brakes really hot coming off the track and sat for a minute or two with the brakes applied. That'll melt a patch of pad material onto the face of the rotor and that will definitely cause pulsing brakes. Now, the reason I think that is that the factory brakes on the GT350 are huge compared to most other high performance cars. They have specially made two-piece rotors that can't warp because they float as a ring on the inner hat. Pulsing with this type of rotor usually means pad material stuck on somewhere.

Also, you said you don't have brake cooling, but the GT350 comes from the factory with cooling ducts built in - it's very efficient.

 

[RES_22]

Check the Stop-Tech website "white papers"...look for the one that explains how to easily rehab your rotors...remove street pad deposits.

Easy, effective and kinda fun.

 

[rdcoleiii]

I get about 14 track days from rotors and pads at RA. This includes an 140 mile roundtrip drive to the track and back each day. Stock pads and rotors. 2020 GT350. I was getting a little vibration when braking into turn 10a. Rotors had a little hairline cracking. I think sometimes I don't get a good cool down lap. Someone crashes and we have to come in. What rotors are you using? For some reason the 2020 rotors are different than previous years. And cost twice as much. Look me up next time at RA. I usually do Chin and JTI.

 

[OPMustang Tim]

Check and make sure you have a pad compound that matches what you are actually doing with it.

ROTOR Paint

 

[OPMustang Tim]

And not to be that guy but Girodisc's offer some advantages with track use and racing compounds in the form of cooling capacity and materials.

 

[EF1]

And not to be that guy but Girodisc's offer some advantages with track use and racing compounds in the form of cooling capacity and materials.

Are Girodisks cryogenically processed?

 

[Bill Pemberton]

OP Mustang is spot on, raced with Girodiscs for years on Vipers, Mustangs , Miatas and more and they are solid. I do not think they are Cyrogenically treated but I have never seen any real difference on the ones I tried over the years. Girodisc rotors are made in the US, and we ( my past occupation ) were using them over Brembo and Stoptech rotors on Vipers. MoPar rotors were made by Stoptech, so over them also. A bit less expensive, but solid life and keep the hat and just get some new rings when you need them. OP Timothy is not being the guy, he knows how solid they are!

 

[EF1]

You don’t have to sell me on Girodisks. I’m already running them on the front. Rears are not available yet. Others have praised the benefits of cryogenic treatment. If they are not cryo treated I am thinking about having my next set of rings treated before assembly.

 

[Jamesmcga]

I get about 14 track days from rotors and pads at RA. This includes an 140 mile roundtrip drive to the track and back each day. Stock pads and rotors. 2020 GT350. I was getting a little vibration when braking into turn 10a. Rotors had a little hairline cracking. I think sometimes I don't get a good cool down lap. Someone crashes and we have to come in. What rotors are you using? For some reason the 2020 rotors are different than previous years. And cost twice as much. Look me up next time at RA. I usually do Chin and JTI.

View attachment 90137

View attachment 90138

I’ll be out there Monday you are around.

 

[Jamesmcga]

So just finished a couple sessions at Road Atlanta and every time I come off the track I still hear the brakes touching the rotors. Is that normal?

I think that’s why I’m going through rotors because it’s leaving pad material on there every time I come off the track and let the car sit even though I don’t have the brakes applied.

Thoughts?

 

[Vettel-ish]

So just finished a couple sessions at Road Atlanta and every time I come off the track I still hear the brakes touching the rotors. Is that normal?

I think that’s why I’m going through rotors because it’s leaving pad material on there every time I come off the track and let the car sit even though I don’t have the brakes applied.

Thoughts?

This can be common with new pads and rotors as the tolerance is sooo tight right now. It will go away after 1500 miles or so.

However if they are not new you might need to dig some more. Maybe calipers. Or pad not set right.

 

[dragoon]

So just finished a couple sessions at Road Atlanta and every time I come off the track I still hear the brakes touching the rotors. Is that normal?

I think that’s why I’m going through rotors because it’s leaving pad material on there every time I come off the track and let the car sit even though I don’t have the brakes applied.

Thoughts?

This can be common with new pads and rotors as the tolerance is sooo tight right now. It will go away after 1500 miles or so.

However if they are not new you might need to dig some more. Maybe calipers. Or pad not set right.

On my previous track car (not a mustang), I had the same issues. It was a caliper piston (2 puck slider type) sticking keeping pressure on the pad during cooling. It was only 1 piston on the front on 1 side & it did cause rotor to cool unevenly and cause the rotor some runout plus excess pad material was deposited.
Have you done any rotor runout measurements ?
The photo attached is what my condition looked like when I got home and was doing post track day inspection. The second photo was after sorting it all out for the next track day.

 

[Jamesmcga]

On my previous track car (not a mustang), I had the same issues. It was a caliper piston (2 puck slider type) sticking keeping pressure on the pad during cooling. It was only 1 piston on the front on 1 side & it did cause rotor to cool unevenly and cause the rotor some runout plus excess pad material was deposited.
Have you done any rotor runout measurements ?
The photo attached is what my condition looked like when I got home and was doing post track day inspection. The second photo was after sorting it all out for the next track day.

View attachment 91731

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My rotors look like your second one so they appear to be normal. I can just hear the pad touching the rotor face as I’m coming off the track at idle speeds. The rotors have two track weekends on them, I don’t really daily it. The pads have about half life left; Ferodo DSUNO pads.
I was thinking that there’s some sort of failure going on inside the caliper itself, but the wear on the actual rotor looks to be even.

I hate sending it to the dealer because half the time they don’t know what’s going on, but I think that’s my last resort. I’ve gone through three sets of rotors and the car only has 4000 miles and about 3500 of those are at the Track.

 

[Dave_W]

How do the GT350 caliper piston dust boots and seals hold up to track use? Could it be a dust boot got charred and is keeping a piston from pulling back in?