[Terry M. Hunt]

Replacing the original rotors on my 71 GTO that I bought new. The original rotors miked out at .980 and the shop I use for machine work felt this would leave them right at the minimum thickness of .965 after turning. I searched around and found a reproduction available from Inline Tube under P/N 11189 which featured the shallow groove machined in the front and rear surfaces, just as the original factory rotors had. Received the new rotors today and gave them a close inspection. Found some very small imperfections in the surfaces of each rotor as shown in the attached pics. Do these look significant enough to affect how well they will work, how safe they are to use, etc?

[Andretti]

Those are minor surface imperfections and wouldn't affect braking performance. The main issue with shipped disc rotors is warpage from incorrect handling, stacking, dropping. If you have a dial indicator you could check run out or have your machine shop mount them to their lathe and check.

Your original rotors visually look good and aren't undersized so I assume you had a brake pulsation?

[694.1]

I am sure they gave you the blem price...

[Terry M. Hunt]

No pulsation. I just had a very annoying dry, scraping, screeching noise every time brakes were applied. There was still a ton of pad material left so I figured I would just install some new pads and use the silicone lube that came with them on all the appropriate contact points between the pads and caliper. The rotor surfaces looked okay, but I thought I should resurface them if installing new pads. By the time I had that done, it appeared I was going to be very close or actually at the min thickness of .965 so I began to search for new rotors and especially wanted ones that matched the originals. I’ve maintained this car meticulously for 50 years, and really did not want to give up my original rotors, but also don’t want to push my luck by hanging on to them past the point where they are safe. I searched for NOS rotors, but could only find one located in UK. There are many aftermarket rotors available. Bought a pair of Delco rotors but kept searching for reproductions with the wear indicator groove that the originals had. That’s how I wound up with the ones in my pics. Interesting that they as well as the Delco rotors are made in China. Not thrilled about that, but it is so often the reality we face today. Have done some preliminary checking with a digital caliper and things look good so far. Same for checking fit of bearings and seals. Agree I need to check runout next, then maybe I’ll be convinced to go ahead and install these things.

[Andretti]

Nice that you've owned her that long! I think the rotor groove is there to help remove dirt/rust scale from the face when brakes are applied. Unlike your brake pads there's no built in wear indicator,

[Terry M. Hunt]

Yes, I had a discussion in the 70-72 GTO forum about exactly what the purpose of this groove was. Various opinions, but yours seems likely why the groove was there. My first guess was a wear indicator, but that seems unlikely now that the rotors have miked out at .980 with a discard dimension of .965 and yet there is still plenty of this groove visible on the face of the rotor.

[Terry M. Hunt]

Got both rotors installed. Driver side runout was .002 and passenger side was .001. Moving ahead with new pads, etc.

[Terry M. Hunt]

This is probably the third set of pads that have been installed on the car. I recall an issue on the last two installs that were many years apart that I’ve noticed again on this install. The shop manual tells me to clench the outside pad’s eats at the slot where they fit onto the caliper. The manual says to do this until there is only .005 clearance radially and tangentially between the ears and the caliper. I’m not sure how this could ever be accomplished or why such a precise clearance is required. This little clearance would seem to indicate that the outside pad was to have virtually no movement up, down,forward, or backward. However, the rest of the design of the pad seems to indicate that this is not what is intended. The holes in the pads that the caliper bolts pass through are considerably larger than the bolt diameter so that clearance can’t be eliminated without hindering the calipers ability to slide back and forth on the mounting bolts. Anyway, it doesn’t look like a little movement in the outside pad is a big deal unless somebody can explain to me why I should be concerned with what I’m seeing. I’m sure it would help if I did disc brake work more than once every 16 years!

[Andretti]

The outboard pad shouldn't have any movement after install. That way, the pad doesn't chatter or click on apply/release and it reduces harmonics or vibration when braking that can cause brake squeal and uneven pad wear.
Many ways to secure the pad. You can have a helper apply the brake then chisel hammer down the ears. Another easy way is wedging a chisel between the rotor hub and bottom of the pad backing plate, then chisel hammer down the ears. Can't understand the .005" clearance their recommending.

[Terry M. Hunt]

I have the ears bent down tight enough that there is no movement of the outer pad up or down in the caliper. However, the slots in the caliper that these ears fit into are wider than the ears, so there is still some slight movement possible fore and aft and I don’t see how this can be eliminated. I don’t want to wind up twisting,distorting, etc. the pad backing plate in the process.

[Terry M. Hunt]

Completed the brake job and have taken two test drives. No noises while braking. Car stops straight and true. Tried gravity bleeding of brakes for first time and it worked great.