I had a Mercedes roll-off 20ton dump in France that had a large magnetic brake on the driveshaft. It was like a large disc but no contact or friction, and that sucker really helped braking. It uses the differential gears as a force multiplier. My F550 has 4.88s. Hmmm, I wonder if I can add a brake like that to my F550. I haven't seen one yet in Texas, and 3 shops I asked had not either, except for one guy who remembers a customer that had a brake right behind the transfer case on a GM 3500 dually (!). Surely that's not standard GM equipment.
Had one that came on my F Superduty, “F450” it was on the back a ZF5 transmission though not as you described, it was a drum brake. Worse POS ever to have ran about $1000 per each time one went out “often” and couldn’t hold the power the truck put out when pulling heavy and hard.
I think you’re describing a driveline retarder. And, yes, they have them. Pretty expensive. https://www.telmausa.com/ Had an F600 with hydraulic brakes and a drum brake on driveline for parking brake.
Yes, now that you mention it, TELMA was cast into the side. Too bad they're so spendy. Thank you.
Decades ago we ran E350 Ford ambulances (dually with a big box on it) and they had Telma retarders to keep from eating brakes. Worked beautifully. Took a tremendous amount of battery power when on. Had some relays (4 stages) that occasionally needed work but not much. They were very heavy and were their own bearing carrier so took a good deal of drive shaft work to install.
I have a GM Topkick with the drum parking brake on the driveshaft. Don't forget to make sure it's off. Heard of someone else starting a grass fire driving across a field. Strong magnets could work. I helped install some super strong magnets to slow down the Mindbender roller coaster. They replaced mechanical brakes that required constant repair and rebuilding with weld. The box they were in even said Caution Extremely Powerful Magnets. Special alloy plates bolted to the cars and they went in between the magnets.