Bloody hell I learnt to drive in an old 2000 series Daf.
Jakes open the exhaust valve just as piston hits tdc to release any pressure so there is no effort spplied to the piston on the downstroke so the engine sort of operates in reverse.
Some good vids on youtube.
Daf have their own version based on the jake they called it DEB Daf engine brake.
I have only experienced rear wheel lock on a jake equipped truck when empty.
