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Rotor Hotspots

PowerDemon

Autocross Champion
Location
Richmond, VA
Car(s)
Golf GTI, Camaro ZL1
Hello everyone,

A month or so ago I picked up a set of used Stoptech 355mm rotors and ST40 calipers with Stoptech pads. The kit was used on another users car for approximately 7,000 miles before I bought them. I was told that they were bedded in correctly. I have no reason to not believe this statement as everything looked good during my initial inspection and I have not had any issues until recently roughly 1000 miles later. When I put the brakes on I had the entire system flushed and replaced with fresh OEM brake fluid. (I know I should have replaced with better fluid but I was in a pinch)

The past three triple digit stops I have made the car shakes on deceleration even with minimal pedal pressure. The vibration increases with more brake force. This only happens at speeds above 90mph. I have no issues with normal around town driving. I got back from Mexico today and checked my rotors are sure enough they have hot spots now. Great. Now I did some research on this topic and I found that this can be caused by improperly torqued caliper carriers and or wheels. I do not believe this is the issue as I am meticulous with torque specs and I made sure everything was torqued to the appropriate specifications and seated correctly. I believe my problem is that I accidentally swapped around the pads causing them to be on the other side of the rotor than they were previously. I believe another contributing factor is that I did not do a bedding in procedure because I believed that it only had to be done once, and now I see that that is not the case and I should have bedded them in again.

Based on my research I believe I have three options. 1 being resurfacing my rotors and bedding it all in again. 2 is attempting to bed everything in again as it sits now despite the vibration. My fear with this option is I might make my situation worse and further damage my rotors. But this is the easiest and most cost effective option if it works. Option 3 is replace everything and start fresh. I only see this as an option if the other two prove to be unsuccessful.

Any insight would be appreciated. Thank you.


TL;DR What is the best way to get rid of rotor hot spots?
 

GTI Jake

Autocross Champion
Location
Charlotte, NC
I don’t believe you’ll find a shop willing to resurface two piece rotors.

For what it’s worth I had a similar experience with my ST40 on a trip to The Tail of the Dragon. Everything was fine until we were almost there and I started getting some high speed vibrations. We pulled off and I check everything visually, and decided to proceed with our trip. Once we got into the good part and heated the brakes up it resolved itself and never happened again.

So long story short I believe both my and your issue is pad deposits, which are easily resolved with some hooning
 

PowerDemon

Autocross Champion
Location
Richmond, VA
Car(s)
Golf GTI, Camaro ZL1
I’m going to call my local tire shop and see if they’ll do it Monday morning. Jake I am glad to hear that. When you experienced vibration did you see any hot spots on the rotors when you inspected them? I’m thinking if I just bed them in again they should sort themselves out, but again I don't want to damage anything if my situation is too bad.

So I just went out and checked the torque on the caliper carriers and the bridges and everything looks good. No issues. But I believe I confirmed my suspicion of accidentally swapping around the pads. From the photos you can see the severity of the hot spots and you can clearly see the areas where the pad is not making contact with the rotor creating the hot spots making me think they were bedded in on opposite rotors. Still not really sure what I should do here. Feel free to share your thoughts. Thanks

Driver side rotor and pad.

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Passenger side.


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aaronc7

Autocross Champion
Location
USA
Car(s)
17 S3
What compound pad is that? I've had good results running aggressive track pads on the street to 'clean' off the rotors, then they are ready to be used with whatever set of pads you have.
 

PowerDemon

Autocross Champion
Location
Richmond, VA
Car(s)
Golf GTI, Camaro ZL1
Hmm. I’ve read about that, but I really have no other use for a track pad besides this situation. It’s not out of the question though. I’m currently running the Stoptech “Sport Pads”.
 

aaronc7

Autocross Champion
Location
USA
Car(s)
17 S3
Stoptech sport pads, or as they were called before "stoptech street performance" or the "309" pads have had a history of forming deposits if not driven hard enough or if not bedded properly. I read that is why they eventually came out with the "street" pad, something a little less aggressive that would work better for guys who arent using them as hard.

Anyways-- I would do a re-bed and go from there!
 

GTI Jake

Autocross Champion
Location
Charlotte, NC
The pictures look like they back up the pad deposit theory. I'd definitely go do some aggressive braking to clean them off, but keep in mind they need to cool properly before coming to a complete stop or they'll just get deposits again.

Local tire shop is the last guys id want anywhere near my Gti lol, that's the equivalent of asking a kid from a ten minute oil change place to install your new turbo
 

PowerDemon

Autocross Champion
Location
Richmond, VA
Car(s)
Golf GTI, Camaro ZL1
The pictures look like they back up the pad deposit theory. I'd definitely go do some aggressive braking to clean them off, but keep in mind they need to cool properly before coming to a complete stop or they'll just get deposits again.

Local tire shop is the last guys id want anywhere near my Gti lol, that's the equivalent of asking a kid from a ten minute oil change place to install your new turbo

Ok I’ll keep that in mind. I plan to follow Stoptech’s brake bed procedure word for word so hopefully that’ll fix it.

I completely agree. I don’t even like taking it to the dealer... I had no intention of taking them the whole car. I was going to remove the rotors and bring them to the shop if I decided to get them turned down lol.

Thanks guys!
 

MonkeyMD

Autocross Champion
I had the same thing as Jake happen. For some reason, when I parked the car for a while, maybe it was after a hot run, when I drove off, it was like brakes were stuck and there was a little vibration on braking. A couple hard stops later and all was back to normal
 

jmblur

Autocross Champion
Location
Massachusetts
Car(s)
2017 Golf R
I had the same thing as Jake happen. For some reason, when I parked the car for a while, maybe it was after a hot run, when I drove off, it was like brakes were stuck and there was a little vibration on braking. A couple hard stops later and all was back to normal

Very common way to get bad pad deposits. If you can, drive around at highway speeds for a while to cool the rotors before coming to a complete stop. If you're DSG, don't engage the parking brake if the brakes are still hot. If you're manual, toss it in gear and find a flat parking spot and do the same.
 

aaronc7

Autocross Champion
Location
USA
Car(s)
17 S3
Very common way to get bad pad deposits. If you can, drive around at highway speeds for a while to cool the rotors before coming to a complete stop. If you're DSG, don't engage the parking brake if the brakes are still hot. If you're manual, toss it in gear and find a flat parking spot and do the same.

When you put the car in P in a DSG car.... what holds the car in place? And how is that different than the parking brake-- parking brake is rear wheels correct? First DSG car, this is my noob question of the day, lol.
 

jmblur

Autocross Champion
Location
Massachusetts
Car(s)
2017 Golf R
When you put the car in P in a DSG car.... what holds the car in place? And how is that different than the parking brake-- parking brake is rear wheels correct? First DSG car, this is my noob question of the day, lol.

The transmission locks very similarly to a normal automatic, where a parking pawl (mechanical lock) engages a toothed ring to lock up the transmission. This does mean the transmission is being used to hold the car, which isn't something you generally want, so you normally SHOULD use the parking brake. But for autocross laps, leaving it in P is perfect. Almost always a flat parking area (we drive on a runway so dead flat), brakes are hot so I don't want to leave the parking brake sitting on the hot rotor, and it's not going to be bumped or anything.
 

aaronc7

Autocross Champion
Location
USA
Car(s)
17 S3
The transmission locks very similarly to a normal automatic, where a parking pawl (mechanical lock) engages a toothed ring to lock up the transmission. This does mean the transmission is being used to hold the car, which isn't something you generally want, so you normally SHOULD use the parking brake. But for autocross laps, leaving it in P is perfect. Almost always a flat parking area (we drive on a runway so dead flat), brakes are hot so I don't want to leave the parking brake sitting on the hot rotor, and it's not going to be bumped or anything.

Thank you! Was really just curious how the "P" works on this car, good to know.

My C5Z used to be my track slut, so definitely tracking on the hot brake / don't set the parking brake thing. Sometimes I would just drive around the paddock a bit if I didn't get a great cooldown lap or something.
 

billbadass

Drag Racing Champion
Location
your moms house
nobody will resurface those rotors, but you can get some cheap track pads like Hawks are famous for grinding the rotors down and drive on them for awhile and they will grind the rotors flat if the "get them hot and bed them in again" doesn't work well, i had the same thing happen to a set of rotors once from not letting the car cool down enough when bedding in new pads. super annoying. if you google this though you'll find what pads people use to fix this. for real track day cars this is not uncommon

the audi ttrs or audi rs3 little brake ducts you can find that mount on the control arms are cheap and easy way to help with cooling also if you haven't done before
 

PowerDemon

Autocross Champion
Location
Richmond, VA
Car(s)
Golf GTI, Camaro ZL1
So I got the Hawk Performance 9012 pads and ran them according to the Stoptech instructions to clear pad deposits and they appeared to clean up the hotspots and pad deposits perfectly. When I was done the rotors looked brand new. So I tossed the Stoptech Street performance pads back in and went out to go bed them in. I performed the Stoptech break in period by the book. 10 stops 60-5mph 90% force. The brakes felt better and better after every stop and I didn’t see any smoke or smell any brakes which is normal since the pads are not new. However when I got home I inspected the rotors and now they appear to be getting too hot with a huge purple ring on each rotor. This confuses me because I didn’t get any brake fade whatsoever. Other than the purple rings the rest of the rotor looks like it's starting to deposit pad material quite well. I’m really at a loss here and pretty fed up honestly. Should I run another bed in? Are these rings evident of excessive heat or something else? I'm open to any suggestions. Thanks!

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