at around 40 mph my recently finished fj45 shakes like a mofo as well as under hard braking. could it be:the 3" longer shakles on the back(the pinion angle looks okay),a unbalanced driveshaft or maybe tires?anything else?
I had a similar problem when I installed new lift springs a few years ago..found that the u-bolts were not completely tight after a few days of driving the rig..After re-torquing everything back to specifications, I had no further problems.
actually the truck did this when i bought it a year ago (i thought it was just unbalanced tires) with original shackles. and i've put new tires and wheels on it as well so i think its driveshaft, u joint or brake related. when i reaf on the drive shaft it does not move(up and down).its smooth slower and faster than around 35 to 45 mph