If your axle lube looks like chocolate milk, then you have water in your differential, and that's BAD! Here's how I realized my problem, and what I did about it.
I'd had the Jeep for about 2 months and somehow never got around to doing the things you should do first. I was getting ready to go up north to go four wheeling, so I thought I should check the gear lube (or at least make sure there was some in there). I unscrewed the little plug from the cover, and much to my surprise, stuff just started pouring out! I say stuff, 'cause it wasn't just gear lube anymore. At first I thought that they must have parked it on a 30% slope, then filled it, to get that much stuff in there. Then I realized that it was half full of WATER! I never personally saw what gear lube and water look like mixed together, so I was expecting to see water separately floating on top of gear lube or vis-versa, but that was not the case. They actually mix together to form chocolate milk. I like chocolate milk, but this had quite a funky smell.
The differential vents through a vent at the top of the housing. The vent is a small hole with a little cap over it to allow air to flow in and out, but keep out big chunks. The purpose of the vent is to avoid pressure building up in the housing as the fluid and air inside heat up from use. Without the vent pressure build up in the differential housing forcing fluid to leak out somewhere it doesn't belong. Unfortunately axle designers don't take into consideration were Jeep owners drive their Jeeps, and because of that, the vents don't do an adequate job of keeping water out while still allowing air to vent. To help keep water from getting in there again, I decided to run a length of hose from the housing to the top of my engine compartment.
I went to "unscrew" the cap in the top of the diff., but what I got was a square piece of metal with a round top on it. It wasn't "screwed" in at all, it was pressed in. Since the square body was tapered, the plug didn't completely seat in the hole, so it left a space between the square sides and the round hole. This is how it's vented. Judging by how much extra fluid was in there, and by the tiny spaces for airflow around the plug, I estimate that they must have parked it in a river for a couple of hours while they ate lunch or something.
Here you can see where the original "plug" type vent was. I put a blue wire
through the hole. See arrow. I decided to drill and tap the hole to accept a
fitting, and run a vent hose up to the top of the engine compartment.
To drill the hole out so that I could tap it to a pipe thread size, I had to
remove the alternator belt and swing it out of the way. It was actually very
easy to reach the differential housing this way. At first I though I would
have to drop the axle somehow!
I went to NAPA and picked up all the parts that I didn't have laying around the garage. I told him what size hole I had and he gave me a drill bit, tap, hose fitting, and 6ft of hose that all matched. I wasn't sure if I'd need the drill bit, but what the hey, I will probably need it in the future.
Off to work I go. I took off the diff. cover and scraped all the RTV junk off. I then used a wire wheel and cleaned the cover inside and out. I took it outside and primed and painted throughout the course of the day. I did the same to the bolts. I always take advantage of times like this to get one step ahead of the rust when I can. The gears seemed to be in great shape considering the quality of the lubricant, so I just wiped everything clean and stuffed a towel in there to begin drilling. The hole was already the correct size, so I didn't need to do this. I moved on to tapping the hole. The NAPA guy gave me a piece of advice, he told me was to put a wad of grease on the tap to collect all of the shavings. Good idea! I put the grease on and every thing was going good. I was almost through the housing when I felt the tap go SNAP! It broke off flush with the housing.
O. K. now what? The tap was turning easy, in fact I was only using one hand? How did I break it? How do I get it out? I looked inside the housing, and could see the end of the tap poking through the hole. It was soooo loose that I turned it out with a needle nose pliers from the inside. It was just a faulty tap I guess. Boy did I luck out! I went back to NAPA to complain, and get a new tap so I could finish the job. When I got there , they didn't have another tap, so the guy was nice enough to lend me the tap from their shop tools :-) .I went back home finish the tap and returned it. The gave me credit for the broken one, so I bought a neat little filter I could put in the end of my new vent hose to keep parts out.
I also bought some gear lube because I couldn't find mine. Everything else just winged along at this point. I threaded in the hose fitting with a little RTV on it for good measure and attached the hose. 6 ft sounds like a lot, but I only had about 5" to spare when I was done. I ran the hose along the top of the frame and up above the battery.
I then replaced the newly painted cover and gasket and cable-tied the hose, leaving some slack for axle droop, but so much that its touching other stuff.
My back axle is already done, but I still need to do the same for my transfer case and my transmission. I'm just going to put a T in the line down by the fame, and they will all share the same vent tube.
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