Grooved rotor??? WTF?

[69customS]

Maybe someone can explain this one to me... its on both sides of the rotor.  I just pulled my brakes apart and found this on my driver's side.  

I'm scratching my head on this one... along with 3 other motorheads. 

 

[Ringo64]

Wow, that's pretty deep and consistent, chance of being accidental are small  

[Frosty]

It appears as if a piece of metal/rock, perhaps your brake pad cracked, or a rivet came in contact with the rotor and wore a groove into your rotor. The fact that it happened on both sides is uncanny. Is there any obvious damage to the brake pads themselves? I can't believe someone would intentionally and deliberately install, much less manufacture such a defective part.

Of course I've heard of drilled and slotted rotors to eliminate pad gas, but this is not one of them.

[69customS]

It is most definitely a machine groove... no rock created that.  Its exact on both sides and at the same depth and same shape. 

[TWO LANE BLACK TOP]

Way back in the day when we ran enduro races... At one of the local short tracks around here... the rules required us to run stock brake and suspension 

parts so some of the guys would cut the rotors like that in order to help

vent the gasses in an attempt to gain a little extra braking power when the rotors were red hot....Weather it actually worked or not is debatable.........

That's what it looks like to me........

[Frosty]

Would it make that much of a difference on a stock street car though Two Lane? If you were building a high HP monster or a corner carver I’d understand. 

[TWO LANE BLACK TOP]

Honestly weather or not it actually made any difference is up for debate

As to why they did it on a street car ..Who knows......

[JUSTA6]

I've seen these in Road racing at Waterford Hill back in the 70's.   Remember guys talkin about weather it really helped transfer heat from the pads or not.  Back then there was only asbesto's brake pads. None of the ceramics N such we have to play with today.  Don't see any heat relate cracks on the face.  I'd turn em and use em.  Justa my 

[Last Indian]

20 hours ago, Frosty said:

Would it make that much of a difference on a stock street car though Two Lane? If you were building a high HP monster or a corner carver I’d understand. 

 

20 hours ago, TWO LANE BLACK TOP said:

Honestly weather or not it actually made any difference is up for debate

As to why they did it on a street car ..Who knows......

Actually that was an OEM option on some cars, my Z had grooved rotors. Two Lane is dead on!

It is a proven fact that the degradation of the brake pad compounds release a gas when heated and you know from physics law that a gas is a fluid. So basically that gas create a type of lubrication between the pad and rotor causing — you guessed it brake fade! That single groove helps elevate that gas. Cross drilled rotors or slotted rotors do the best job though. Look a any of the bikes (motorcycles) all their rotors are drilled or slotted. Their rotors are also hardened. 

The problem or short sightedness of the OEM with the groove was since it was circular with the pad in time it no longer functioned.

Point of reference below, you can still get these as reproductions.

70-75 GM Front Disc Brake Rotors Grooved W30 Judge GS

 

Edited October 2, 2018 by Last Indian

[69customS]

crazy... who would have thunk it. lemme tell you from experience... they suck. Trying to pull off the caliper with the pads in that groove was not easy. I got my new rotors on order ... drilled/slotted for $114 shipped. :0)

 

[Last Indian]

3 hours ago, 69customS said:

crazy... who would have thunk it. lemme tell you from experience... they suck. Trying to pull off the caliper with the pads in that groove was not easy. I got my new rotors on order ... drilled/slotted for $114 shipped. :0)

 

Yup, that's what happens because the groove is symmetrical with the pad and rotor rotation!

A little hint, if in the future you have trouble getting a caliper/pad off a rotor because of a lip or groove do this. Take a large screwdriver or the like, place it between the rotor and an open area of the caliper, non piston side, usually through the top opening of the caliper. Lever the screwdriver handle back towards the non piston side of the caliper. This will collapse the piston back into it's bore creating a larger gap between the pad and rotor allowing the caliper to come off easily.