Just put in some 4.10's in my buddies car. this is the 3rd set i've put in an 8.8 and the first set with issues. I used the ford tool for the pinion shim, and set backlash at .010. used some paint on the gears and the setup looked perfect. Installed them in the car, and it whines, loudly, only when there's torque to it. when you're off the throttle it's completely silent. also, when going over bumps it's quiet, even when in the gas a little. what could this be? the gears were used and they did have a couple knicks and chips, but i deburred all the sharp edges and figured it'd be ok. any ideas?

 

its likely because of the gears themselves

 

i've never had a problem like it before, would it cause any damage?

 

Check to see if the pinion nut didn't come loose.

 

problem with used gears is you need to set them back where they were originally set up, meaning on the same wear pattern, and if you didn't take them out of what ever they came out of, your throwing a blind dart, and if they were originally set up wrong, no matter where you set it it'll make noise