This would be a non-hunting gear set, 39ring 12pinion. Each pinion tooth should make contact with every 3rd ring tooth, and since 39 teeth is evenly divisible by 3, the pattern will repeat itself. Looked at the other way, each ring tooth will always have the same 4 pinion teeth contact it. So, this set would definitely need to be timed.
Here's how I proved it: make 39 dots across a paper representing the ring teeth. From the left, start numbering under them 1-12, when you get to 12 just keep on numbering from 1 again, when you get to the end of the row just keep numbering at the left again on a new row. After 4 times across, you'll see that all combos are set to repeat again starting at the beginning of the 5th row! Hope this helps.
'66 Coupe EFI T5, power Granada swap, homemade awesome power rack & pinion steering, great cruiser.
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