Rear End Vibes
 

Stock 1991 Pickup, 4WD, Ex cab with 250k miles on it. I recently replaced my rear third member with a rebuilt third from East Coast Gear Supply. When I replaced the third, I replaced rear wheel bearings and all seals. Before I did the third member swap, I had zero vibrations. When I drove away from the shop after the swap, I detected a pretty bad vibration around 45mph that can be felt all the way to 60. After that it's hard to detect. The vibration is still there when I put the truck in neutral at speed so it's not engine related.

I've had the tires and wheels balanced (no change), I replaced one axle that was out of spec (no change), I replaced both rear brake drums (no change), and had my driveline looked at by a driveline shop. They balanced my driveshaft and inspected U-joints, carrier bearing, and CV joint, and said all looked to be in fine shape. They did note that there was an excess of grease packed into my slip yoke to the point where it was difficult to get the shaft back into the truck and attached to the pinion flange. They took out the excess grease which they said was packed hard like a rock and the vibration has decreased, but is still definitely there. The guy also said that when he listened to the rear third member with a stethoscope it sounded like I had a bearing starting to go bad, like one of the bearings was moving freely out of it's retainer (this before I told him it shouldn't be since it's a brand new rebuild from ECGS).

At this point I'm wondering if there was some issue with the third member (maybe it got dropped during shipping and bent the pinion flange just slightly?) and might see about getting another one sent to me under warranty unless I get some other ideas. Thanks for the help.