cwaynem

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?

lionelhutz

Runout didn't cause it.

Peterbuilt

Good thing you found that crack when you did.

Mike Ward

The runout wouldn't affected it one way or the other, but it seems there's either a casting deviation or machining mark inside the rotor where the crack initiated(?) Is there a similar spot 180* opposite?

cwaynem

Anyone have any idea what would cause a crack like this?

cwaynem

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.

mds3013

Have you had Mike look at the rotor? He is the best I know. It looks really thin in the pic.. mike...

cwaynem

Good idea. I'll take it off and bring it down with the differential.

qwank

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

cor66vette

Don't mind me for asking, but why was "Bubba" working on your car in the first place?

Arkyvette

I'm gonna guess casting flaw. You are missing one of the vanes there right where that crack is. It would be mighty tough to pry a vane out of a rotor.

cwaynem

Could be. I noticed there is no fin behind the area that cracked. It looks like the fin took a piece of the wall with it.

qwank

it's possible the factory drilled that spot out to balance the rotor. I actually have a weight installed in my right front rotor from the factory (still riveted onto the hub)

cwaynem

Bubba? I just bought the car very used a few months ago. I keep discovering surprises the PO left behind.

diehrd

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

Easy Mike

At some point or another, Bubba has worked on almost all C3s.

CA-Legal-Vette

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.

scottw

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.

Mike Ward

C3 calipers don't slide, they're fixed in place.

diehrd

I done to many non- c-3 breaks to remember ;;; 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.