The local auto parts store sold me from what I thought the pinion bearing for the pinion on my new set of gears,but for some reason this bearing just slips on and off with no effort.Considering this is the bearing thats needs to be pressed on.Do you need to put the pinion shim so that the bearing doesn't come off.

I went to several stores I bought two different bearings,same part number

HM89249 is this the correct one that needs to be pressed on the bearing?

 

Both bearings are pressed on. The inner bearing (near the gear) is pressed on using hydraulic press. This bearing also secures your bearing shim pack.

The outer bearing will be forced on when you install the pinion, outer bearing, crush sleeve, yoke and nut and begin to tighten everything up.

You must have the wrong bearings or wrong pinion.