Cracked rotor
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Joined: Oct 2012
Posts: 86
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From: Lucas TX
Cracked rotor
I heard an thumping noise from the differential on my 76. I am fortunate to live near tracdogg2 and he checked it out and determined the differential needed to be rebuilt. As I was removing it, I noticed this on the rear rotor.
It looks like it goes all the way through.
I just had the rotor off when I repaired the parking brake. Bubba removed the shoes and all the hardware for me, so I had to rebuild it. After he "fixed" the parking brake, he did not align the rotor access hole with the parking brake adjustment hole, so I put it back on right. I did not check the runout when I rotated the rotor to align the holes. I have put less than 100 miles on it since I fixed the parking brake. Could runout have caused the crack?
It looks like it goes all the way through.
I just had the rotor off when I repaired the parking brake. Bubba removed the shoes and all the hardware for me, so I had to rebuild it. After he "fixed" the parking brake, he did not align the rotor access hole with the parking brake adjustment hole, so I put it back on right. I did not check the runout when I rotated the rotor to align the holes. I have put less than 100 miles on it since I fixed the parking brake. Could runout have caused the crack?
Last edited by cwaynem; Mar 24, 2013 at 08:12 AM.
Thread Starter
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Joined: Oct 2012
Posts: 86
Likes: 2
From: Lucas TX
There is no crack at 180, just the one side. I have not taken it off to see if there is a casting or machining mark underneath. It seems to stop before it gets to the drum portion of the rotor. I know I will have to replace it, but if there is an underlying problem, I want to fix it too. I would prefer to only replace the rotor once.
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Le Mans Master
Joined: Feb 2011
Posts: 5,943
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From: Southern NH
looks like when Bubba removed the rear shoes, he probably had a hard time taking the rotors off and stuffed a screwdriver in the cooling fins to get leverage, and then cracked the rotor. It was probably unnoticable until recently
Le Mans Master
Joined: Aug 2001
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Safety Car
Joined: Jan 2009
Posts: 4,000
Likes: 299
From: New York
A hung up break could cause that , so make sure your caliper is not sticking when it slides and that the pistons move freely . That rotor would also cause a thumping noise along the drive line so be sure you need a rear diff and not just a rotor 
Race Director
Joined: Jul 2004
Posts: 12,705
Likes: 329
From: Scottsdale Arizona
Kind of looks like it has been drilled out in this pic. The factory or the manufacturer would not have done this to balance it. Not sure why anyone would. I suppose that it's possible to break out a fin and leave it looking this way but the hole is pretty round looking.
Burning Brakes
Joined: Oct 2001
Posts: 1,241
Likes: 4
From: Okinawa Okinawa
Love finding surprises. Even after owning since 2001, I keep finding little things everytime I open something new up.
Haven't seen a rotor like that. Glad you found it and it didn't cause any damage.
Haven't seen a rotor like that. Glad you found it and it didn't cause any damage.
Safety Car
Joined: Jan 2009
Posts: 4,000
Likes: 299
From: New York
But a sticky piston will cause rotor failure . Someone mentioned it looks drilled ? I do not see any tool marks in the photo to see a drill was used.