When the hub is pumped full with grease some old grease has to be removed. Grease when heated will expand and will push out the seal. Also never have the bearings to tight as this also will heat up the bearing and grease can't create the film between the cone rollers and cubs. I'm still old fashioned and check tires and bearings by hand.
Forty years ago a Mack service mechanic had the left front bearings to tight. In the middle of the night while driving down the road the oil in them started a fire, lucky it was snowing and put it out with snow. The flames where 2 ft. up.
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ALJO 'Forever Young @ Heart' provide on their travels Music Entertainment to Senior Care Homes