1968 911L Rear Brake Disc Machining

[schip]

Hello -

I have a 1968 911L (USA version) that has the vented rear disc brakes (picture of backside of disc below) and wide caliper with the 'dogbone' spacers.

As I am planning to replace the brake pads and e-brake shoes I wanted to have the disc surface machined at the local auto store. They are not willing to do so because they cannot find the specifications for minimum thickness. In the 2nd picture (side view of vented disc) their is 9.0mm from the mid-line of the vented slot to the outboard edge (bottom in picture), and 11.0mm from the mid-line of the vented slot to the inboard edge (top in picture).

Does someone have the minimum dimensions handy? If I am below tolerances then I am ready to purchase the pricey replacements

Thanks in advance for the expertise. Stewart.

[Neunelfer]

18.6 when reconditioning and 18 mm when replacing for 20mm vented rotors*.

*The disc must always be machined on both sides by the same amount.

[schip]

Eric -

Thank you for the prompt and informative response.

According to these specs the disc has not been previously machined, and I should remain well within acceptable tolerances after they machine the 2 surfaces. The grooves on the disc surface are minimal so I don't expect they will need to remove a lot of material. There is no lateral run out either.

Kind Regards. Stewart.

[Neunelfer]

If one side is down to 9mm then I doubt you could machine the other "equally" and get 18.6mm.

You're close though...