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Is there a vent/breather on the differential of the AD trucks? I am leaking axle grease onto the wheel and brake on the passenger side of my 53. Sounds like the seal but before I do anything I want to make certain the vent/breather (if there is one) is not blocked. where will i find this critter?
Thanks.

Olblu49,
I have a 52AD. The vent is on the top of the axle housing on the drivers side. It is half way between the diff and the hub. Hope this helps.

Thanks! I'll look for it first thing tomorrow. I imagine it can be removed and cleaned if necessary.

It's a small pipe fitting with a sheet metal cap. Unscrew it and it's off.

My '54 GMC one was not threaded. It has grooves that look like threads at first glance but if you look closely they are not. I turned and turned before popping it out with needle nose vice grips. Then I popped it back in with a whammer.

I found the vent fairly easily. Guess I should have looked before I posted! But as you get old you find yourself lying under a truck for much longer than it takes to make the repair!
When I found it the metal cap was pretty well stuck in place. With a bit of effort from my pliers I freed it so that it swivels with just finger pressure. Don't know that by freeing it up will help it vent. I tried to pry it off but did not want to do any damage. Thanks.

They usually plug up internally. Sometimes you can pry the cap off, then you can run a wire down, sending the grit into the oil in the housing. Wire brush around the base and look for threads. That will tell you if it unscrews or has to pull. It really needs to be unplugged, or your new seals will blow out when the oil gets hot.

Eliminate the cap all together. Get one of those cheap coil air hoses, cut a section off, and run it up to the frame rail, or even the firewall, like I did. Mine didn't have threads, so I took a brass 1/8" NPT nipple and tapped it in with a hammer. Works like a charm! No worries about the little cap plugging again!

Axle vent

Cletis - earlier you mentioned that your breather looked threaded and so does mine. However now that it is out there is no easy way to pry the cap from the stem. big61fourby mentioned using a 1/8 NPT and tapping the fitting in. May try that but really would like to pry that cap off. It is presently soaking in a can of WD40.

Withthe help of a propane torch I freed the cap and it swivels/rocks nicely now. Won't need the NPT fitting after all. Thanks all for the help.