C3/C4 rear rotor "interchangability"?

Just a somewhat academic question here. In the quest to take some weight out of my '69 I never looked into seeing if early C4 rear rotors would fit on the back of a C3. Both have similar parking brake setups (diameter difference?) and somewhat similar overall diameter. The C4 rotor is lighter, which isn't a big deal as the rear brakes on a C3 seem to be mostly just along for the ride, as I could beat the dickens out of my car and the rear pads barely showed any appreciable wear. The width difference isn't a big deal either, as a thermal spacer could be employed to take up the difference.

So like I said, it's primarily an academic question as I don't have the C3 suspension under it anymore, but I'd just like an answer to my curiosity.

Thanks,
Mike

The rear C4 rotors are only .82" thick

If you are swapping I'd use the later C4 PBR caliper or a set off an F body, they are super light and have an integral parking brake.

Twin_Turbo said:

The rear C4 rotors are only .82" thick I know. That's why I mentioned putting some thermal spacers in there to make up the difference.
If you are swapping I'd use the later C4 PBR caliper or a set off an F body, they are super light and have an integral parking brake.

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I'm not swapping. I'm already there. I was just curious if this would be a possibility for reducing the (unsprung) weight for C3 guys who have the stock trailing arms. In my experience the heavy stock C3 rear rotors are overkill for these cars.

easiest would be the wilwood calipers, they are aluminum..easy no brainer solution. just $$$$

The C4 rear rotors have a pretty shallow offset (I think). That would push the caliper out towards the wheel unless the thinner disk allowed you to leave the calipers where they are as you suggested with the thermal spacer. Suppose you would have to convert the parking brake to C4 also.

Yes, they have very little offset

Twin_Turbo said:

easiest would be the wilwood calipers, they are aluminum..easy no brainer solution. just $$$$

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You're missing my point. You're still stuck with the weight of an oversized C3 rear rotor even after swapping calipers. I'm just curious about getting a couple more pounds off a car by putting a lighter (and inexpensive!) rotor back there.

I hauled a bunch of old C3 and C4 rotors to the scrap yard when I moved last year, so I don't have any loose parts laying around anymore. I was hoping someone might have a couple of old rotors that they could measure and see if there are enough fitment similarities to warrant further investigation.

BBShark said:

The C4 rear rotors have a pretty shallow offset (I think). That would push the caliper out towards the wheel unless the thinner disk allowed you to leave the calipers where they are as you suggested with the thermal spacer. Suppose you would have to convert the parking brake to C4 also.

Click to expand...

The later C4 rotors have minimal offset, but the early C4 rotors are visually similar to C3 rotors.

I was interested in seeing if the parking brake drum/hat diameter was anywhere similar.