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post #1 of (permalink) Old 12-06-2000, 06:43 PM
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Y is my rear diff breather spitting out gear oil?

after a 40 mile road trip i noticed that my diff breather had shot out gear oil. why did it do this. is it cause the oil is bad? it only has about 8000 miles on the oil. its and amc 20.

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post #2 of (permalink) Old 12-06-2000, 07:23 PM
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Re: Y is my rear diff breather spitting out gear oil?

naw-8000 not too much for gear oil.
bad gear oil? i doubt it.
over filled it? don't know how you could cause it will spill out when filling.
where does the breather hose end at? is this the front or rear diff?

post #3 of (permalink) Old 12-06-2000, 07:29 PM
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Re: Y is my rear diff breather spitting out gear oil?

If it's an AMC 20 it must be a rear diff. The oil got hot and expanded, then took the shortest route out to relieve the pressure. I'd say it might have been a little overfilled? Did you add any funky additives? It might also have been blocked, built up pressure, and when she blew took some oil with it. 8K is not a lot of mileage for the oil, unless you submerge it often or mud run it.

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post #4 of (permalink) Old 12-06-2000, 07:34 PM
 
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Re: Y is my rear diff breather spitting out gear oil?

Mike,
more info,
Have you had it any steep hill climbs or off camber hills lately? Where is the hose located? Where do you live ie: what have the temperatures been like?
One scenario is that if you have a dirty vent tube and accumulated gear oil is not dripping all the way back into the diff, then if the temperatures out side is very cold the air in the axle tubes is cold and dense, as you drive the bearings heat up and cause the cold air to expand, this causes the clog to rise in the vent tube pushing up the oil above it, viola oil leaking out of the vent tube, Remove your vent tube and force some parts cleaner and compressed air through it, and see what happens.
I always install larger than stock vent tube fittings and tubes, it helps in keeping the axle tubes well ventillated, which greatly reduces water being drawn into the axles through the outer seals and bearings.

Jeff
89 YJ
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post #5 of (permalink) Old 12-06-2000, 08:12 PM
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Re: Y is my rear diff breather spitting out gear oil?

i live in colorado at 5000 feet. its cold out the day it did it i started driveing at 8:30 am. so it was real cold out. i did some off camber dirveing a week befroe but mostly on the road in the last week. i dont think it was over filled. so it sould have been the extreem difference in temp. i'll take the hose off and clean it. it is rooted up inside the little space behind the fender whell. where the gas filler is.

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post #6 of (permalink) Old 12-06-2000, 08:13 PM
 
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Re: Y is my rear diff breather spitting out gear oil?

I have this same problem with my CJ-5. After about 10-15 min of highway driving if I stop, it will spit gear oil out the vent tube. I cleaned the vent tube and extended it higher up but it still does this. My vent tube is on the passenger side and runs up to the body tub on the passenger side. Mine is also an AMC 20 rear with 4.10 gears if that makes a differance? Mine would spit out quite a bit of oil until the diff would actually get low on lube. My rear pinion is also tilted up with a degree shim to line it up with the CV driveshaft which I'm sure makes the problem worse. One tip I got from this BBS was to add about 6 ounces of ATF to the diff to help keep it from foaming. It still spits out gear lube but not nearly as much.

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post #7 of (permalink) Old 12-07-2000, 08:09 AM
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Re: Y is my rear diff breather spitting out gear oil?

What's happening is the oil is getting into the tube, as mentioned, probably through off-camber, heat, or whatever means. Now, because the tube is small and capped on the top (a restrictor cap at that), and it is the only vent, the oil won't drain back down the tube. So each time this happens, a little more oil gets into the tube, and it remains plugged, so the diff won't breathe. Now, when you go from sea level to a higher altitude, you're going from a high pressure zone to a low pressure zone, which creates a suction on the diff (equalizing pressures), and causes some of the oil to come out, like sucking through a straw. On the heating issue, it's because the diff is actually being cooled when it's run, the ring gear brings oil into the air inside the diff and cools it slightly. It also disperses the oil around the diff, which has contact with the atmosphere, and is cooler (same principle as air cooled engines). When the jeep stops, the oil heats up slightly (due to lack of the cooling from rotation), and to relieve the pressure, vents out the tube, which has oil in it. There are 2 corrections to this problem:

1) Rip the stock junk off. Pull the fitting off the axle as well (it's pressed in, not screwed), and get a 1/8" NPT (National Pipe Thread) tap. Thread the hole (I use a vacuum cleaner to suck the metal flakes up so they don't go into the diff), and put a larger compression fitting on there (no clamps needed to hold the hose). Thread it in, and use like 1/2" hose, run it to the same spot. I use a small filter for the top, can be found for engine breathers, and are common. The whole mod will cost about $10, including the NPT tap.

2) Put another breather on. This will allow a second avenue for the oil to drain back into the diff. Kind of like a straw. If you put a straw into liquid and put your finger over the end, then pick it out of the liquid, the liquid stays in the straw. Now it you remove your finger from the liquid (add a second breather), the liquid goes back into the glass. It can be done the same way as the first method, which is just what people do, so you don't often find 2 breathers on rigs. It's also a second possible point of intrusion for foreign objects into the diff. The good thing is that you can run a smaller one so it doesn't need to be as large.

Either of these should solve the problem. I went one step further and linked all my breathers together on the jeep, ran the hose up by the roll bar for deep water (mini snorkel). I use 1/2" hose everywhere, and it's clear so I can see if oil (or anything) is in it.

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