You are assuming all fast food workers made the same... they didn't.
For instance, food prep/food counter people made weekly $191 for men and $160 for women.
https://www.bls.gov/opub/mlr/1985/01/rpt1full.pdf
$191 in today's money is about $515, assuming 40 hours That's about $12.87 If you go instead for purchasing power.. it is $636 $15.9
If you go for relative income compared to per capita then it goes quite a bit high to be about $20.07
You know... looking through all these the only jobs today that paid the same (or more) were those in tech, that's it. Every other sector has seen less.
I edited my post my original post seems things moved since then.
I wasn't lying. I actually posted the BLS information and the wages in a couple of years ago.
Depending on what method you're using to determine what that money is worth now you will get a range. I went for purchasing power, if you compare to per capita though well.. the numbers are quite a bit higher, but this was only a decade after the decline and the huge gulf that became the wage gap and what do you know.... we get to a number close to the $22-23 it would be today if pegged to productivity.