Leaky front diff breather

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.


Feb 2, 2004
Hayward, Ca.
I know there are threads out there, but I am kinda stumped. I did the front axle service on my 93 a few months back after buying a terribly neglected triple locked 80. After a few weeks of driving (after service), I noticed that my breather was puking front diff oil out. I checked for the condition of the front diff gear oil and it was contaminated with some moly birf grease (gear oil was black). I drained, refilled and temporarily left the breather off as I thought it might be a bad oem breather and all was fine for a couple months while driving like this. Well, about a month later, knowing that there was a open front diff breather hose under there, I decided to go to Mr. T and get a new oem breather and slapped it on. 2 weeks later (present-if you're following), I find my front puking diff oil again.. Why does my rig not like oem breathers? I have other 80's and I am running oem breathers and all is fine. Should I just slap on a small fuel filter instead of the oem breather and call it a day? As mentioned before, seems everything is fine once there is a fully vented filter or no oem breather on...
Last edited by a moderator:
The front axle breather check valve is crap.

Get 8' of 3/8" fuel hose (or similar) & plug into the axle, run other end up the firewall & near the master cylinder.

Ziptie it there & cap with a cheap inline fuel filter.

Problem solved for good.

Bonus points - run some more 3/8" hose from the rear diff all the way up to the firewall & cap the same way.

You now have extended height breathers & they never plug / choke.

My 450 had an issue even when I swapped check valves with the black 80, the above fixed it so I did it to both.
Sounds like your axle is way too full of lube. Norma full level is below axle shaft, so how would it get grease clear up to the top of the axle tube to acess the breather?
  • Like
Reactions: RFB
It's 1/4" fuel hose, not 3/8".

The gear oil level increases because it has sucked moly from the birfs.

When you swap the breather, did you remove the fitting and clean and open the fitting as well as the hole in the axle?

When I did mine, the fitting and hole we're clogged so I had to use a pick to scrape the hardened gear oil/grime from the inside of the fitting as well as the hole. If the axle cannot vent, it will push gear oil out to the birfs as it heats up. Then as it cools, it sucks in moly from the birfs. Lather rinse repeat.

Yes, the level can increase, as I had it happen in mine. Once I cleaned the fittings and did the hose and fuel filter, the problem disappeared. That was 5000 miles after an axle rebuild. I now have 48000 on the rebuild with no recurrence.

Users who are viewing this thread

Top Bottom