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Front Brake Disc Discolouration On The Inside

V28VX37
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V28VX37 Veteran

V28VX37

Posted
Posted

Hi all,

I was working on the car recently and noticed a curious discolouration of my front rotors. It's only on the inside edge of the disc on both sides of the car. Otherwise the discs look fine, even wear and no signs of cracks.

I have DBA T3 4000 Series slotted rotors all around with the standard R34 GTT Sumitomo calipers, Remsa 650C pads, HEL braided lines and Dixcel high temp fluid.

The rotors have about 15,000 km and two Sandown track days on them.

Has anyone else seen this, is it anything to worry about?

Could the inside of the disc be running hotter because of the backing plates and less airflow?

Cheers

23944999079_e90789b50f.jpg

24286679276_53b20d61e6.jpg

MrStabby Grand Master

MrStabby

Posted
Posted

My guess is its just some water splashed up on the inside then dried off. The paint stripes (there's three IIRC) are temperature indicators. Google for details on that.

If there's no issues with brake operation and feel, I would ignore.

V28VX37 Veteran

V28VX37

Posted
  • Author
Posted

My guess is its just some water splashed up on the inside then dried off. The paint stripes (there's three IIRC) are temperature indicators. Google for details on that.

If there's no issues with brake operation and feel, I would ignore.

Thanks Adam. Yep I know about the temp indicators, it's just the rotor colour that got me puzzled. There's no effect on braking performance that I've noticed.

R31Nismoid Grand Master

R31Nismoid

Posted
Posted

Not sure what you're asking from the pics?

Nothing looks out of place either way.

And also, next time you can - cut off the shield on the inside face off the rotor. It just keeps the heat in :)

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V28VX37 Veteran

V28VX37

Posted
  • Author
Posted

Not sure what you're asking from the pics?

Nothing looks out of place either way.

And also, next time you can - cut off the shield on the inside face off the rotor. It just keeps the heat in :)

Cheers. See how half of the inside 'edge' part of the disc is gray instead of rusty red like the rest of the disc edge? That's what I was referring to.

But yeah I'm wondering if I should DIY some brake ducts, might save the heat shields for that :)

R31Nismoid Grand Master

R31Nismoid

Posted
Posted

Ah, yeah ok. See what you mean.

It's more protected there I guess with that heat shield on - or could be, because the heat is being kept in :)

But 100% cut the shields off, if doing brake ducting that'd also be good

GTRPSI Mentor

GTRPSI

Posted
Posted (edited)

Ah, yeah ok. See what you mean.

It's more protected there I guess with that heat shield on - or could be, because the heat is being kept in :)

You could be right.

Notice the temp paint has lifted off that area? Probably cooked it good and turned the rotor blue on the inboard side. :)

Edit, what colors are the 3 temperature markers going from left to right?

If they are White Yellow White, you cooked that baby good, well over 650 degrees, id say the inner part of the rotor went over 900 degrees and glowed a nice cherry red color, hence the burned off paint. :D

Edited by GTRPSI
WantGTR Mentor

WantGTR

Posted
Posted

Ah, yeah ok. See what you mean.

It's more protected there I guess with that heat shield on - or could be, because the heat is being kept in :)

But 100% cut the shields off, if doing brake ducting that'd also be good

This is interesting. Has anyone else cut off the rear shields??

R31Nismoid Grand Master

R31Nismoid

Posted
Posted

Pretty much anyone who does track days down here mate, has cut them off their cars, whatever model/make they may be.

You cant get ducting working that well generally with them anyway.


Weird it's a SA defect item. I mean, if you cut them do it looked factory... They wouldn't even know?

GTSBoy Grand Master

GTSBoy

Posted
Posted

Pretty much anyone who does track days down here mate, has cut them off their cars, whatever model/make they may be.

You cant get ducting working that well generally with them anyway.

Weird it's a SA defect item. I mean, if you cut them do it looked factory... They wouldn't even know?

Depends on who is looking. Your average cop might or might not have any idea. The dream boats that are all gung ho about busting modified cars will know. The guys at Regency will all definitely know, and if your car is defected for something else and is in for an inspection, or you're getting an engine transplant signed off and getting it inspected, then they will look and they will see. What happens then depends on why you're there, how nice the guy is and whether anyone else is watching. The guy who inspected my car for the engine transplant was really nice, a real car guy, and he let me go with a couple of small things (with a polite demand that I deal with them) rather than failing the inspection. But everything else on the car was tested and inspected. Dash lights and dimmer, demister, rubbers on the door catches, ride height, dents in the chassis rails (none, because I fixed them), etc etc. Any of those things failing can be your undoing here.

GTSBoy Grand Master

GTSBoy

Posted
Posted

Yuh, I think it is something that falls into the category of "modifying a braking or steering system" (to paraphrase their various publications) on which the rules are pretty much "don't touch anything unless you get it engineered"....and they apply that rule in blanket fashion as it is easier than thinking. Rock shields might not do much......but they are there and they were put there by the factory, so there they must say unless someone smarter than all of us says they can come off.

  • Like 1
V28VX37 Veteran

V28VX37

Posted
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Posted

Ah, yeah ok. See what you mean.

It's more protected there I guess with that heat shield on - or could be, because the heat is being kept in :)

But 100% cut the shields off, if doing brake ducting that'd also be good

Ok cool, do you just cut around the hub or do the shields come off somehow?

You could be right.

Notice the temp paint has lifted off that area? Probably cooked it good and turned the rotor blue on the inboard side. :)

Edit, what colors are the 3 temperature markers going from left to right?

If they are White Yellow White, you cooked that baby good, well over 650 degrees, id say the inner part of the rotor went over 900 degrees and glowed a nice cherry red color, hence the burned off paint. :D

Yeah I'm pretty sure they'd be cooked, my December track day at Sandown was in 37 degrees :woot: That said I did do heaps of cool down laps and never noticed any degradation of braking performance.

I'll check the temp markers when I get the car back, it's at the shop getting the steering rack recoed.

Note to self: Never move to Radelaide. That Regency thing sounds like a major PITA.

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