How do you set the pinion bearing preload on a 91 gmc van and what is the torque on the nut?

To set the pinion bearing preload on a 1991 GMC van, you'll need to use a beam-type torque wrench to measure the rotational torque while turning the pinion. First, tighten the pinion nut to a specific torque (typically around 20-30 ft-lbs) to seat the bearings before checking the preload. Then, continue tightening the nut in small increments while checking the rotational torque until you achieve the desired preload, usually around 8-12 inch-pounds. The final torque on the pinion nut is generally around 40-50 ft-lbs, but always refer to the specific service manual for your vehicle for exact specifications.