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Diff fluid from vent, Ford 9"

6K views 14 replies 10 participants last post by  AlwaysWantedA55 
#1 ·
I am just starting to drive my car after an 8 year build. I have a narrowed Ford 9" with a Detroit Locker. I've noticed small deposits of diff fluid on my floor, but haven't found an active leak. Today after 30 minutes on the freeway, it was pushing oil out through the vent....I would guess it's probably put 4-6 ounces on the floor.

The housing is fabricated, the vent is on the top of the axle tube. I'm guessing that the heat from my freeway cruise caused it to build pressure, and it's getting rid of some oil--meaning I may have overfilled it.

Is that a reasonable assumption or could this indicate a problem?
 
#2 ·
If it built pressure, that would imply that the vent hole isn't big enough, or was blocked temporarily.

You might have overfilled - usually you'd only fill to the bottom of the fill plug hole on the 3rd member. I see some fabricated housings with a fill port on top of the housing, which is nice for convenience, but you still should have the normal fill port open when filling.

Now that it's puked some fluid out, you might run it where it is for a bit and see if it continues to push fluid out and whether the fluid level remains where it is now.
 
#4 ·
I had that problem with my recent install....also a Ford 9". In my case it wasn't a heat/pressure problem, the gear was just spitting oil up at vent. I never had more than a drop or two on floor, but I had lots of spray on the back of my car after driving. I ended up using a heavier gear oil (Lucas 85/140), adding a long vent hose up toward floor of car, and picked up one of these from Currie enterprises.
http://www.currieenterprises.com/CE-9028F

Not sure if it was one, or a combination of all that solved the problem, but its not spitting gear oil any more.

Ace
 
#5 ·
The vent hose should be at least 12-14 inches, and preferably have a loop in it to prevent oil from coming out the top.
My 9" Ford hose is 20" long with a wide loop, and extends up towards the body about 12 inches.
 
#6 ·
While putting a hose or hose loop on the vent will do something, that's primarily for trucks and SUVs to keep water out of the axle, as in when launching a boat, or just driving through high water.

When I referred to the "fill plug" on the 9", I'm talking about the one on the driver side of the 3rd member.
 
#7 ·
Some gear lubes foam and 'twist up' in the housing and can climb out a flush mounted vent. My solution is to run tubing with a loop to a hole in a nearby section of frame/crossmember. my experience is the loop with a vent on the end up in the frame solves the problem. As a trade, help me seal up oil leaks on my 400SBC with 6"rods (wrist pin in oil ring land with support) rev-limited to 6600 using 10-40 Rotella. leaks front cover and rear seal.
 
#10 ·
if the engine has an exhaust system with mufflers, this doesn't work in my testing. Open headers and no problems.

I had a problem with the same thing on a small block, ended up being the new, cheap 7 quart pan being built poorly and not aligned/sealing correctly. I tried a bunch of different gaskets, finally dumped that pan and went to a good quality pan and problem solved.
 
#14 ·
4 to 6 ounces sounds like a lot more than spitting some oil out of the breather because the axle spun some oil off. I would think that much would lead you to being overfilled. The oil is expanding and being pushed out of the vent. I guess if it is overfilled, it will eventually get low enough to stop spewing, but, like mentioned earlier on, look for the pipe plug in the side of the cast case/pumpkin side and remove it. let anything run out until it stops, or fill it until it just starts to come out.

If it still does it....it is another's turn.
 
#15 ·
I agree...I'm using a fabricated 9" housing from S&W Racecars. I don't have the car home now so I can't look, but from looking at pictures of my build it looks like the filler hole MAY be slightly higher on the housing than the level of the vent--so filling it to the opening would then be over-filling it. I'll get down to my shop tonight, get it on the hoist and take a good look. Meanwhile, I've got a catch can on the way--fitting for the vent bung into a hose, feeds into a vented catch can, returns the oil to the housing when everything settles down. May be overkill, but I really don't want to dump oil
 
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