For the last couple of days I have been getting a roar louder than usual from the rear diff. and a vibration...I jacked the truck up today, put it in gear, and noticed something I thought was strange.

The Plastic peace in the pic....Should it be spinning with the rear-end or should it not move at all...Does this mean my pinion seal is bad???and needs immediate replacement, or is it suppose to do this?

Thanks in advance to those who respond quick....I need to see if this is trouble so I can get it in the shop today!

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yes that is your seal. it should be spinning.

 

are you sure that it's not a tire problem?