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Q: Rear diff grinding noise

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My truck will go into reverse but not in to drive. When I give it gas in drive it seems like it wanted to go but something is holding back. I looked underneath the truck and the drive shaft will turn half a rotation when given gas.( 2000 rpm) the. I forced it up to 3000-4000 rpm and the car went forward but made a loud grinding noise coming from the rear diff but it still goes into reverse just fine. Also the truck will roll back in neutral but not forward

My car has 169000 miles.
My car has an automatic transmission.

Try unbolting the drive shaft from the rear axle and place the vehicle in neutral to see if the vehicle will roll in either direction first. If it acts the same as when the driveshaft is connected, then the rear differential should be drained and the cover removed to inspect the internals. It is possible that the ring gear or pinion gear may have broken or sheered a tooth or two. This may be preventing the vehicle from moving one way and not the other. If this doesn’t help, then have the vehicle towed - from the rear - or flat bedded to your nearest repair shop for a diagnosis.

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