Dom99GT

Need some advice, filled my diff to the top of the fill plug, now after a short drive it's purging from the spring relief valve on my 88 foxs left side Axle, is this normal because of overfilling? Never seen it before

mongolchuck

Should only fill it until it just starts to run out of the fill hole. Also unthread the vent and check to make sure it's clear, and reseal it with some thread sealant. There should also be a hose with a little breather on the vent.

Boss_Hotrod

Be sure to fill it to the factory hole on the front of the diff. The covers usually have a fill hole higher than the factory one which can cause over filling.

Buck Sergeant

Dom 99GT, momgolchuck and Boss Hotrod are right on the money. I can't stress how important it is to replace that axle tube vent. I was told there is a TBS stating to replace said vent with a new OEM vent. I did it on my 2014 GT after changing rear-end gears and am now breathing easier.