There is a hole in the rear axle. Is this normal? Will this be a problem?
I think you are talking about the ventilator hole on top of the axle.
When the gear lube heats up it greats pressure inside the axle housing, the ventilator releases the pressure.
Otherwise the pressure could push gear lube pass the axle seals into the brakes drums and out the pinion seal.
It should have a
vent cap that screws into the threaded hole.
Group # 5.387 part # 3738462 ventilator
GMC axle explodedChevy axle explodedGMC and Chevy 1/2 ton axles are virtually the same.
Venting the Differential Jim Carter Tech article
There usually is no problem unless you plan on submersing the axle in water, like living in a flood plane area.
That is probably what happened, the truck was driven in high water.
The cap might of been broke off and you will need a Easy Out to back out the threads that are still remaining in the axle housing.
