1990 Ford Bronco, 150k miles, 9" rear end (axle code 19). Truck has started
leaking diff oil out the top of the vent hose on the axle, OCASSIONALLY.
When it does, look out, it leaves a drip about 1.5 feet long (I park facing
uphill in my driveway, but it's not real steep-when parked on this hill, the
vent hose fitting on the axle is about level with the filler plug). What
would cause this leak? It does not do it often, just every now and then.
I've noticed that when changing my oil, the diff ALWAYS needs oil, and lots
(a quart or more) it may be leaking out the hose while I'd driving but I
can't really observethat-skid plate on the gas tank has a midsize oil mark
where the vent cap is fastened to it. Does anyone have any ideas? I
thought that perhaps air is becoming entrained in the fluid causing it to
expand, then when the car stops, the air comes out of solution, but above
the vent line and displaces the oil out the vent. Please respond to the
group.

 

I could be wrong and probably am. But I think that valve is there for overflow. So if you've been adding to it, it's just dumping what it doesn't need.

 

 

Your overflow hose could be clogged! There is a possibility of pressure building up and blowing oil through the seal. I would suggest you remove the hose and see that it is clear. Remove the differential cover and completely drain the unit. While the cover is off check to see the breather hose hole is clear. Throughly clean the mounting surfaces and re-seal with a quaility RTV silicon, refill to the bottom of the threads and then keep an eye on it.


Bob

 

I have the same problem...What do you do in a case where the differential does not allow access? (Mine the sealed no back access-type diff)

 

The Ford 9" requires pulling the axles out of the third member before you can remove it and service the seal. As there is no inspection cover, the third member must be unbolted and pulled forward to service it and the gasket. Itsa gonna be a heavy little bugger too, so take the necessary steps to ensure gravity doesn't kick in when you least need it to. (Transmission jack comes in handly right about now). The axles must be pulled far enough out the clear the splines in the differential. Requires removal of the outer bearing retaining plate (behind the drum brake assembly) and a slide hammer attached to the wheel flange to tap the bearing free of the axle housing.

As for the problem of the axle dumping oil from the vent tube, make sure that the end of the tube is above the top of the axle housing and check to be certain there is nothing in the housing that shouldn't be....like water! If the vent tube is damaged, water can come into the housing through the hole. Not good.

 

I did a little investigating under my truck and in the Hane's Manual last night. It looks like I have a bad pinion seal. The manual said that I need to take the wheels and brake calipers off to eliviate stress to the whole unit. Then It states that I would need to remove the drive shaft, get torque specs on the pinion/yolk nut (use the torque wrench and rotate entire assemble around a few times to determine torque measurement). At that point it suggests reomvoing the nut and using a dual-jawed puller to remove the pinion, seal and so forth. Have you ever done this before? I have worked on many engines, but not diffs? Is it very difficult? Any suggestions? Do I still need to pull the axles...the book said nothing about it. Thanks for your help so far!

 

If its the pinion seal, no, you shouldn't need to remove the axles. You will have to deal with getting the flange or U-joint yoke off the rear end though so you can access the seal. This requires dropping at least the rear portion of the driveshaft from the rear end. I have not personally performed this repair but someone here has and will be able the shed more light on the process. May want to toss this question out in the transmission, tansfer case, and differential forum.

 

Thanks Joe I will try posting...and even do a little searching over there as well! Thanks Much!!!!

 

what would happen if water went inside the differential? Passing through Tucson, AZ last month I drove through about 30 min. worth of heavy rain. That is as heavy as it gets here in the Southwest. I was having problems with the abs speed sensor and when I replaced it noticed that the breather hose had been torn off at the connector. I am going to clean out the diff tonight and put fresh new oil. Aside from the obious, missing gear teeth and all, what should I look for.

 

sluggslime,

Look for "sluggslime" of a grey/brown color inside the axle housing. Its what happens when oil and water try to mix...you get this really nasty looking, smelling, feeling sludge that settles to the low points inside. Not pretty and potentially fatal to the gearing. At any rate, I would drain and inspect the rear end and clean anything that looks like that out. If there is no damage to the gears etc. put it all back together and refill it. Get the vent hose replaced ASAP.