Hi everyone, here is yet another problem I have with my Ford 9" rear end. Got my coupe all cleaned up and head out on a Saturday night. I get to where I'm going and I walk around back and the whole lower portion of the car is like sprayed with 90W gear oil. No leaks just blowing out vent ,the level was perfect before I left. I added a longer rubber line to the vent and ran it way higher then it was before. Next trip there was gear oil on back of car again but this time the new hose that was attached to the vent had oil all the way to the top. Now the only thing that is different is the vent itself, A fitting was screwed into the housing that is like a 1/8 inch. Could the smaller fitting make the gear oil to blow out the vent tube ? You can blow into the line and it is clear. any help would be great.
As Squirrel asks where is the vent located. Most from the factory are located on the top of the axle tube well above the lube height. Both of my 9" have what is ether 1/8" or 1/4" pipe thread for the vent to screw into and the hole for the fitting is about 1/4". If your vent is located on the top center of the housing the gears might be pushing the lube out.
Axle vents, as Jim and WW64 alluded to, are like real estate. It is all about location. If you look at OEM applications, the vent is almost always a good 20", or more, away from where any gears are moving. There is a reason for that.
I just went out there and measured from dead center of the pumpkin to where the vent is and it's 7 ", I measured from backing plate to backing plate and it's 49 ". On bumps the axle would come up and hit the exhaust which would damage the vent cause they line up perfectly so now I have a low profile 90 angle fitting that runs it more to the side where I ran the vent line up high so......
As has been said, the vent is usually in an axle tube. They are usually 1/4 pipe thread or larger I have seen cases when a vent in each side was needed. What gear lube are you using and could there be any water in the axle? Water can cause the gear lube to create foam which greatly expands it's volume. You might want to drain and refill. Are you certain you have the level correct? Some have a fill plug at a higher level than the check plug.
Most of the original Ford supplied vents have a .060 / .080 hole a short way up the tube from the threaded area ...This will not allow oil to be passed but will allow air to go through ...Think of it as a "restriction" about halfway up... Anything you install with out the small hole will allow oil to escape .....
My 9 inch is 7/16 SAE thread hole . The fitting has a cone shaped orifice in it to allow pressure out only and oil to drain back . The Pan has a crankcase vent that is a 180 piece of 3/8 tube never drips a drop out , but vents out pressure . Something to think about , over fill and tight bearings building up heat , expanding gear oil level causing a leak . I have never seen a 9 in I owned produce one drop of fluid . Sent from my iPhone using H.A.M.B.
Well It's Friday morning and I have my latest attempt at fixing the vent problem in place so I will take her on a little cruise today and see what happens. I'm seeing a rear end tear down and drilling and tapping in my future
How about you take a 1/4" pipe coupler, weld it where it is easy to get to (on the axle tube) and then run a 1/4" (or smaller) drill bit thru that to pierce the axle tube? screw on whatever hose/fitting/vent. done. Spraybomb if desired.
I've got two 8" Ford rears, the vent is on the passenger side of both, and is a 7/16 SAE bolt thread also, not pipe thread. The original bolt/vent held down the brake line coupling block. Maybe 9" rears are different?
The 6-3/4" rear that came out of my '60 Falcon had that, too. I took it out, and put it directly into the '91 8.8 rear that replaced it. There are some things that Ford just left alone.
I machined a spacer with a curved bottom, because the original brake hose wasn't around. I think it's a 7/16" bolt, with the vent built in, probably original to the 57 Ford housing. No leaks from this rear at this time....finally...