Many people consider the jump button useless, as it only makes Max go about 3 inches in the air. But it makes sense when you remember that his knee is shattered from the shot in the first film, and therefore can't jump very well. Also, when you jump down from a height that's not quite enough to hurt Max, he'll limp on that injured knee for a while.
Max demands that Chum build two large gas tanks for the Magnum Opus to fuel his drive through the Plains of Silence. Chum objects, saying that the tanks would take up his spot in the car. When Max gets the V8 Interceptor, after killing Chumbucket, it has two large gas tanks in the back where Chumbucket would normally stand.
At one point, Griffa directly asks Max what year it is, and how old he is. Max says he doesn't know. Given that at least a full generation seems to have passed, as nobody seems to properly recall much of the previous technology or culture that came before the wars or disasters, and only Max knows the proper words for a number of things, it's entirely possible he's much older than he looks.
Griffa bears a resemblance to Bruce Spence, who played the Gyro Captain and Jedediah. Given the Mad Max series' love for recasting the same actors in new roles, perhaps Griffa was intended as the third "appearance" of Spence, in spirit at least - like Max, he's not a direct likeness, but a similar body and face type.
