Grove in rotor, what's it for - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**JIMs70GMC** · 04-25-2004, 09:41 PM

I pulled the rotors and steering knuckles of the 70chevy and was wondering what the grove was for. the grove is in the center and on both sides. I think it's for wear but it is deep:

71swb4x4 · 04-25-2004, 09:45 PM

The Chevy guy at my parts place said they were to assist with cooling.

mrein3 · 04-25-2004, 09:47 PM

I have the original rotors from my '71 Monte. They have the same groove. I took them in to get resurfaced and the guy at the NAPA counter said he can't resurface them because they are grooved.
I said they came from the factory that way.
He said no.

That was the last time I was in that NAPA.

The old timers tell me that was an attempt at dissipating heat. Remember that is a 1st generation production rotor.

lukecp · 04-25-2004, 09:47 PM

I'm pretty sure the groove was caused by someone letting the pads go to long without changing them.....the wear indicator on the pads made the groove. I think though...not totally sure.

**JIMs70GMC** · 04-25-2004, 09:54 PM

Lucas the grove is perfect and same depth on both side and on both rotors.

I boght new ones for $23 each and plan on replacing them but thought i'd ask.

gmcnorton · 04-25-2004, 10:14 PM

the groove was put in the rotor. it was to help dissapate heat and to reduce brake noise.

**Palf70Step** · 04-25-2004, 10:22 PM

Besides the cooling factor, I'm told they were inthere to help with dust disapation, which I think is what helps reduce the noise. I saw one machine place a few years ago that would not work on them because they were groved.

**MJN** · 04-25-2004, 11:10 PM

I heard those grooves were for helping seat the new pads after doing brakes and guide them until they are seated. They are factory and not made by worn pad rivits.

Rdrdave · 04-25-2004, 11:23 PM

to dissipate heat! When I was a kid I had some other "kid" turn my rotors down until that groove was gone! DOH! I ended up with a new pair of rotors. THose are from the factory with those grooves. Don't turn them out!

lukecp · 04-25-2004, 11:50 PM

Oops then....my '72 had them and i assumed they were from me waiting too long to put on new pads (lots of brake screech and pull). They are practically gone from being turned now...guess i need some new rotors, lol.

**kwmech** · 04-26-2004, 01:39 AM

The groove in the rotor if you measure it is the minimum thickness that it can be machined to. So when the groove is gone so are your rotors.

*Shane* · 04-26-2004, 02:00 AM

I agree with kwmech ... it is a wear indicator.

Jeepster376 · 04-26-2004, 02:06 AM

I have the groove in mine. If they are factory, does that give any indication of age? Would they be original, or were replacement rotors made the same way up to a certain time?

chevy69er · 04-26-2004, 02:16 AM

Well im glad to hear what that groove is really for.When i converted to disc brakes a couple months ago i noticed it,i thought the rotors were bad because i got them from a junk yard but when i thought about it,it did seem like the pads could make an even and uniform groove like that.The guy that machined then down didnt even know what the groove was for either.

drink2mny · 04-26-2004, 03:39 AM

Yeah I have heard the heat dissapation and keeping the pads aligned. I guess it would keep the rattle noise down and pad pretty square on.. My '72 has them and a '76 Dana 44 I once owned had them too..

Dean · 04-26-2004, 07:51 AM

All of my K20s have those grooves with original rotors. I've never had to turn or replace them. Not bad for over 30 year old rotors. You sure they need replaced?

Sweet72 · 04-26-2004, 10:30 AM

Those grooves are there to make it more difficult to get the calipers off!

lol
Like kwmech says, they're minimum thickness indicators.

sneakysnake · 04-26-2004, 11:00 AM

I had a "nut " try to turn mine out

**JIMs70GMC** · 04-26-2004, 07:09 PM

Well I guess I'll just hold on to the new ones and keep the old ones on. Thanks everybody!

Virginia72SWB4X4 · 04-26-2004, 07:43 PM

I believe they're there do dissipate and allow the release of gases created from heating of the pad material. If you look at high performance braking systems they have the groves machined across the rotor at an angle. This is to assist the relaese of gas by the rotating assembly.
They also naturally assist in the dissipation of heat because of the addtional surface area.

04-25-2004, 09:41 PM	#1
JIMs70GMC user # 2756 Join Date: Jun 2001 Location: Chesapeake, Virginia Posts: 4,612	Grove in rotor, what's it for I pulled the rotors and steering knuckles of the 70chevy and was wondering what the grove was for. the grove is in the center and on both sides. I think it's for wear but it is deep: __________________ 1970 K25, 8' stepside bed 350/465/205 44 up front, 60 in the rear 4.10s rolling on 33" Dunlop MTs 1986 K5, 350/465/208 Dana 60/14 bolt from a cucv 36" Super Swampers TSL/SX 1983 K20 w/ CUCV axles, 350/700R4/208 sitting on 37" Goodyears 1986 M1031 6.2 diesel, TH400/NP205 locker in the rear and a LS in the front, all stock for now..... 1986 K30, 350/400/205 dana 60 and 14 bolt. I kept the drivetrain. Body/bad and chassis are gone. 1981 K30, 350/465/205 dana 60 and dually 14 bolt. Has a G80, and a flat bed. Going to replace the flat bed. 1985 K20, 350/400/208 10 bolt and SF 14 bolt. I wonder where I can find some 1 tons. Hmmmmm

04-25-2004, 09:45 PM	#2
71swb4x4 Senior Member Join Date: Nov 2003 Location: Brookings, SD Posts: 10,497	The Chevy guy at my parts place said they were to assist with cooling. __________________ Some people are like slinkies, they aren't good for anything, but you can't help but smile when you see one tumble down the stairs.

04-25-2004, 09:47 PM	#3
mrein3 Registered User Join Date: Feb 2000 Location: Center City, MN, USA Posts: 3,254	I have the original rotors from my '71 Monte. They have the same groove. I took them in to get resurfaced and the guy at the NAPA counter said he can't resurface them because they are grooved. I said they came from the factory that way. He said no. That was the last time I was in that NAPA. The old timers tell me that was an attempt at dissipating heat. Remember that is a 1st generation production rotor. __________________ '70 cab, '71 chassis, 383, TH350, NP205. '71 Malibu convertible '72 Malibu hard top Center City, MN

04-25-2004, 09:47 PM	#4
lukecp Formerly yellow72custom Join Date: May 2001 Location: Austin, TX Posts: 7,531	I'm pretty sure the groove was caused by someone letting the pads go to long without changing them.....the wear indicator on the pads made the groove. I think though...not totally sure. __________________ '72 Chevy C10 Mild 350/TH350/3.07. Ochre/White. Old high school ride. '70 GMC C2500 '62 327 4bbl/SM465/4.56-geared Dana 60. White/White. Project or parts truck. '97 Saturn SL DD. 1.9/5-speed. 40+ highway mpg

04-25-2004, 09:54 PM	#5
JIMs70GMC user # 2756 Join Date: Jun 2001 Location: Chesapeake, Virginia Posts: 4,612	Lucas the grove is perfect and same depth on both side and on both rotors. I boght new ones for $23 each and plan on replacing them but thought i'd ask. __________________ 1970 K25, 8' stepside bed 350/465/205 44 up front, 60 in the rear 4.10s rolling on 33" Dunlop MTs 1986 K5, 350/465/208 Dana 60/14 bolt from a cucv 36" Super Swampers TSL/SX 1983 K20 w/ CUCV axles, 350/700R4/208 sitting on 37" Goodyears 1986 M1031 6.2 diesel, TH400/NP205 locker in the rear and a LS in the front, all stock for now..... 1986 K30, 350/400/205 dana 60 and 14 bolt. I kept the drivetrain. Body/bad and chassis are gone. 1981 K30, 350/465/205 dana 60 and dually 14 bolt. Has a G80, and a flat bed. Going to replace the flat bed. 1985 K20, 350/400/208 10 bolt and SF 14 bolt. I wonder where I can find some 1 tons. Hmmmmm

04-25-2004, 10:14 PM	#6
gmcnorton Registered User Join Date: Aug 2002 Location: Middleport, Pa. 17953 Posts: 737	groove the groove was put in the rotor. it was to help dissapate heat and to reduce brake noise. __________________ 70 GMC SHORT STEP , 71 BLAZER ,72 JIMMY,72 BLAZER, JUST NEED THAT SUBURBAN NOW......WANTING MORE

04-25-2004, 10:22 PM	#7
Palf70Step State of Confusion! Join Date: Jul 2002 Location: Gulfport, MS USA Posts: 47,269	Besides the cooling factor, I'm told they were inthere to help with dust disapation, which I think is what helps reduce the noise. I saw one machine place a few years ago that would not work on them because they were groved. __________________ Bill 1970 Chevy Custom/10 LWB Fleetside 2010 Toyota Tacoma PreRunner SR5 Double Cab - DD Member of Louisiana Classic Truck Club (LCTC) Bill's Gallery Life isn't tied with a bow, but it's still a gift. Live simply. Love generously. Care deeply. Speak kindly. Leave the rest to God!

04-25-2004, 11:10 PM	#8
MJN Registered User Join Date: Feb 2000 Location: Maquoketa, Ia/ Orr, Mn Posts: 3,051	I heard those grooves were for helping seat the new pads after doing brakes and guide them until they are seated. They are factory and not made by worn pad rivits. __________________ '51 South Bend Model "9A" '56 Chevy 3600 NAPCO '74 Chevy Cheyenne Super K20-restored on 37's '72 GMC Sierra Custom K2500- in progress '08 GMC Envoy Denali '12 GMC Sierra 2500HD Denali '17 GMC Yukon XL VCCA member #58596 http://www.nohrco.com

04-25-2004, 11:23 PM	#9
Rdrdave Broke and still trying Join Date: Apr 2003 Location: Alameda, CA Posts: 562	to dissipate heat! When I was a kid I had some other "kid" turn my rotors down until that groove was gone! DOH! I ended up with a new pair of rotors. THose are from the factory with those grooves. Don't turn them out!

04-25-2004, 11:50 PM	#10
lukecp Formerly yellow72custom Join Date: May 2001 Location: Austin, TX Posts: 7,531	Oops then....my '72 had them and i assumed they were from me waiting too long to put on new pads (lots of brake screech and pull). They are practically gone from being turned now...guess i need some new rotors, lol. __________________ '72 Chevy C10 Mild 350/TH350/3.07. Ochre/White. Old high school ride. '70 GMC C2500 '62 327 4bbl/SM465/4.56-geared Dana 60. White/White. Project or parts truck. '97 Saturn SL DD. 1.9/5-speed. 40+ highway mpg

04-26-2004, 01:39 AM	#11
kwmech Senior Member Join Date: Mar 2003 Location: Colfax-California Posts: 8,659	The groove in the rotor if you measure it is the minimum thickness that it can be machined to. So when the groove is gone so are your rotors.

04-26-2004, 02:00 AM	#12
Shane Account Suspended Join Date: Jun 2000 Location: over yonder Posts: 14,270	I agree with kwmech ... it is a wear indicator.

04-26-2004, 02:06 AM	#13
Jeepster376 Registered User Join Date: Feb 2004 Location: Massachusetts Posts: 269	I have the groove in mine. If they are factory, does that give any indication of age? Would they be original, or were replacement rotors made the same way up to a certain time? __________________ 72 Cheyenne Super 4x4 SWB

04-26-2004, 02:16 AM	#14
chevy69er Registered User Join Date: Feb 2003 Location: Lakewood,Ca Posts: 69	Well im glad to hear what that groove is really for.When i converted to disc brakes a couple months ago i noticed it,i thought the rotors were bad because i got them from a junk yard but when i thought about it,it did seem like the pads could make an even and uniform groove like that.The guy that machined then down didnt even know what the groove was for either. __________________ 1969 C-20,383 stroker,sm465,custom long travel front suspension,4 wheel disc brakes,35" pro comps...mods under way include: 4x4 conversion,and custom bumpers.future mods include: gear vendors od unit,and relocation of fuel cell.

04-26-2004, 03:39 AM	#15
drink2mny Registered User Join Date: Jun 2003 Location: spokane wa Posts: 2,189	Yeah I have heard the heat dissapation and keeping the pads aligned. I guess it would keep the rattle noise down and pad pretty square on.. My '72 has them and a '76 Dana 44 I once owned had them too.. __________________ Support The Board



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04-26-2004, 07:51 AM	#16
Dean Senior Member Join Date: Jan 2000 Location: Cincinnati, Ohio Posts: 1,492	All of my K20s have those grooves with original rotors. I've never had to turn or replace them. Not bad for over 30 year old rotors. You sure they need replaced?

04-26-2004, 10:30 AM	#17
Sweet72 Registered User Join Date: Nov 2003 Location: Alexandria, VA Posts: 1,534	Those grooves are there to make it more difficult to get the calipers off! lol Like kwmech says, they're minimum thickness indicators. __________________ '72 GMC SWB C1500 Custom, frame-off in progress. 383 SBC, 9:1CR, Comp Cams XE262H, Scat internal balanced crank, Eagle SIR 6" rods, Keith Black dish pistons, Dart Iron Eagle 72/180 heads, Weiand Stealth intake, Stewart stage I water pump, Holley 4bbl vac sec, TH350 with B&M Shift Improver Kit. 12 bolt positraction.

04-26-2004, 11:00 AM	#18
sneakysnake It's a catastrophic success. Join Date: Jan 2003 Location: Oklahoma Posts: 2,077	I had a "nut " try to turn mine out

04-26-2004, 07:09 PM	#19
JIMs70GMC user # 2756 Join Date: Jun 2001 Location: Chesapeake, Virginia Posts: 4,612	Well I guess I'll just hold on to the new ones and keep the old ones on. Thanks everybody! __________________ 1970 K25, 8' stepside bed 350/465/205 44 up front, 60 in the rear 4.10s rolling on 33" Dunlop MTs 1986 K5, 350/465/208 Dana 60/14 bolt from a cucv 36" Super Swampers TSL/SX 1983 K20 w/ CUCV axles, 350/700R4/208 sitting on 37" Goodyears 1986 M1031 6.2 diesel, TH400/NP205 locker in the rear and a LS in the front, all stock for now..... 1986 K30, 350/400/205 dana 60 and 14 bolt. I kept the drivetrain. Body/bad and chassis are gone. 1981 K30, 350/465/205 dana 60 and dually 14 bolt. Has a G80, and a flat bed. Going to replace the flat bed. 1985 K20, 350/400/208 10 bolt and SF 14 bolt. I wonder where I can find some 1 tons. Hmmmmm

04-26-2004, 07:43 PM	#20
Virginia72SWB4X4 Registered User Join Date: Jan 2004 Location: Fredericksburg, Virginia Posts: 144	I believe they're there do dissipate and allow the release of gases created from heating of the pad material. If you look at high performance braking systems they have the groves machined across the rotor at an angle. This is to assist the relaese of gas by the rotating assembly. They also naturally assist in the dissipation of heat because of the addtional surface area.

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