Maximum wear on brake drum

What is the recommended maximum wear/diameter of a rear drum, P/N 06-2764?

New diameter is noted to be 6.997" - 7.007".

This conversation has been held here a few times previously. There are no factory stated min/max dimensions. Folks can offer you suggestions, but ultimately you on on your own. For what it is worth, I recently turned a front drum, removing 0.020. But the construction of the front and rear drum are totally different and probably shouldn't be compared for this purpose.
Stephen Hill

HA! what a thought, wearing out rear drum friction surface before the chain teeth, good one.

hobot said:

HA! what a thought, wearing out rear drum friction surface before the chain teeth, good one.

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No, I am going to get my Mk2 compliance checked here in NZ, and one of the things they need is a brake certification which measures the runout/ovality on the drum (and front disc) against factory specs.

Ugh, you need this non-existent data for 'govt' licensing reasons, ugh. May have to contact NZ vintage club to find out how they deal with this. I'd give your British Spares vemdor a ping on this and maybe get a signed measurement &/or statement there was no factory spec to match and then your measures to demo its well within reasonable wear, though 'gvot's' don't deal with reasonableness very well. Phil Yeates that was over active here last year till kicked off has really expanded his cycle restoration empire in shop space and crew members business from exhaust fabrication to paint so maybe he's got a handle on this for you.
philyates <philyates7@bigpond.com>

Get an engineer to quote that it has zero runout and ovality.

gortnipper said:

No, I am going to get my Mk2 compliance checked here in NZ, and one of the things they need is a brake certification which measures the runout/ovality on the drum (and front disc) against factory specs.

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Thats going to be interesting when Nortons don't appear to even quote a minimum thickness for discs or max wear diameter for drums,
let alone runout limits.
Then what happens ??

Triton Thrasher said:

Get an engineer to quote that it has zero runout and ovality.

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Don't suppose that giving them a spin and eyeballing that there is no runout counts for anything. ?

The runout limit probably is zero ??, anything else affects braking quite noticeably.
Which is probably a tighter tolerance than they were made to ??

hobot said:

...get a signed measurement &/or statement there was no factory spec to match and then your measures to demo its well within reasonable wear, though 'gvot's' don't deal with reasonableness very well. P

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Triton Thrasher said:

Get an engineer to quote that it has zero runout and ovality.

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Yeah, I am going to fill out the brake declaration, which I am allowed to do on vehicles older than 1991, using my trusty cheap n cheerful digital caliper and photos of the act. I just wanted to see if there were factory specs for minimums. I will just list "new" specs and I am sure the measurements will show they are within "safe tolerances", which is what is required.

On the disc side, I thought I had seen .240 as min thickness, but after looking again I think I interpolated that from the Old Britts page where they wanted it to be .245 to turn it.

It's when the brake judders or pulses that you worry about "out of roundness."