shakel angle

Was told opposite,I have the bottom 25 degrees Back from the top,the explanation I got was that when the rear end gets loaded and pinion goes up it would pull the shackels forward lifting the rear as they go to center thus planting the tires down,The whole reason I just joined this forum Is because I dont quite buy all the info I can get from the slant six forum,more room here for more opinions,Thanks,Mark