Boss 302 diff cover breather vent

[Sjohnson1800]

So I purchased a boss 302 diff cover from south Florida parts. And I didn’t realize there was a breather port on the top of the cover. Am I able to plug this or do I need to add a breather vent???

 

[67GTA]

So I purchased a boss 302 diff cover from south Florida parts. And I didn’t realize there was a breather port on the top of the cover. Am I able to plug this or do I need to add a breather vent???

You can if your axle tube vent is working well now and not leaking. The axle tube vent usually becomes a problem once the car is lowered with 3” over the axle exhaust. For a car that sees the track, you’ll want a diff breather can to prevent hot diff fluid coming out the vent. I would recommend adding the breather can while your changing the cover - the penalties for venting issues is a leaky vent, or a blocked vent that blows out axle seals.

 

[Sjohnson1800]

I have a breather can set up already coming off of the factory axle port so I was thinking I could either add a tee and run to the diff cover or just block it off I wasn’t sure. but seeing as this one is higher I guess it wouldn’t be better plug the one on the axle and run a catch can from here??? You wouldn’t happen to know the thread pitch of both ports. When I did my catch can set up I couldn’t find the thread pitch of the axle port so I’m still using the factory bung and would either like to change it or plug it depending on your recommendation. Thanks!

 

[docs302]

If you track your car you will need a vent somewhere on the rear to manage pressure. The problem with the 8.8 on track, and something I personally experienced, is boiling of the differential fluid. It only happened on high speed tracks where I was really pushing high RPM for extended periods. The simple fix is adding a containment system for the boiling fluid. There are a few options and this subject has been covered here with pictures so you can search for them.

The better option is using the threaded 4AN port on the top of the left axle tube just to the left of the diff. It's plugged but you can remove the plug and use that as your attachment point for the overflow hose. One popular method is a vented catch tank attached inside the car in the spare tire area. Lot's of options for that.

Another is what I have currently and that's the over-axle tank like the attachment below. It attaches with the UCA mount where there is room. The nice thing with this system is that it catches the boiled fluid and then allows it to drain back down into the rear when it cools. Plus, it's not inside the car. (https://lmr.com/item/JLT-AX05/JLT-R...term=4585513249447009&utm_content=SC Shopping)

Last and best option is a dedicated differential cooler if you are really going to be tracking/racing your car frequently and want to eliminate boiling the fluid altogether.

 

[TMSBOSS]

With the can already installed on the axle housing and working. I would simply plug the "Extra" vent hole on the cover. I have been running mine that way for years without problems.

 

[67GTA]

After several failed attempts as making the axle port work I eventually moved from the axle to diff cover, using a -4 port plug on the axle. Thread size is 7/16”-20. I’m not sure what size adapter you’ll need on the Boss cover - I’m using the Whiteline watts link.

 

[Sjohnson1800]

Awsome thanks for the info guys!