Moly or Metal?

[atomicshawn]

Has anyone had a front axle seal leak allowing birf grease into the front diff fluid?

About 10k ago I installed 4.88's and ARBs. After 500 miles I changed fluid and the rear was fine, but the front was dark and metallic looking. Nauseated at the thought of going through the front again, I filled it up with new fluid and hoped for the best. 500 miles later I changed out the fluid again, same thing. Another 500 and did it again, same thing, fluid dark and metallic looking and the rear was clear. I figured at that point the damage was done and continued to drive it and waited for something to happen, abnormal noise, excessive play, something. Nothing abnormal ever occurred.

Today, 10k later I changed the cases again. The rear fluid looked great with a small amount of metal on the magnet. Again, the front was dark and metallic looking, not better or worse than before. Then I noticed the magnet on the front was actually cleaner than the rear, very little metal. So now I'm wondering if maybe I have a bad seal and molybdenum is contaminating the fluid. It looks about that color.

When I assembled it I packed the birf housings a little before I installed the axles so I may have carried some grease in that way, but you would think after 3 oil changes it would be gone.

Thoughts?

 

[Offroads4x4]

Did you replace the axle inner seals? This is the seal that goes out when you have birf soup. Also did you check for any groves and use some Emory cloth to the seal area on the axle shaft to clean things up?
Marlin makes a HD seal for it but many swear by the old factory ones. Use the search function under birf soup.

 

[timer00]

Sounds like a slow leak over time. The front almost always will blend with some grease over time due to the design. I wouldn't worry until you have thin oily grease shooting out all over the brake dust cover and tire like what happened to me and made me have to do the front end ASAP.

 

[atomicshawn]

Did you replace the axle inner seals? This is the seal that goes out when you have birf soup. Also did you check for any groves and use some Emory cloth to the seal area on the axle shaft to clean things up?
Marlin makes a HD seal for it but many swear by the old factory ones. Use the search function under birf soup.

I did replace the inner seals with a kit I got from Kurt at CO. I dont remember if I cleaned the seal surface, it's been a while. I probably jacked up one of the seals when putting it together, I do remember struggling not to lay the wieght of the axles on the seals when I slid them in.

 

[-Spike-]

The birf grease, in my experience, always migrates into the diff. Shouldn't be an issue, not enough gets into the oil to do anything. Oil getting into the birf is a different story, can wash out the grease and then leak out the wiper seal, leaving you with no lube.

 

[atomicshawn]

I get what your saying about "birf soup". And I'm thinking that is in reference the more likely scenario of seal failure which would be gear oil in the housing, not the other way around. Maybe if I over packed the housing, but I don't think I did. It does seem like one housing is a little more weepy than the other though and maybe that’s a sign.

 

[atomicshawn]

The birf grease, in my experience, always migrates into the diff. Shouldn't be an issue, not enough gets into the oil to do anything. Oil getting into the birf is a different story, can wash out the grease and then leak out the wiper seal, leaving you with no lube.

So the discription I'm giving sounds like moly in the diff, and it is common?

 

[-Spike-]

In my personal experience, yes. I wouldn't worry about it, especially if the magnet is clean. You should check your breather tubes though, if they aren't allowing air back in, temp changes can cause the grease to get sucked through the axle seals.

 

[atomicshawn]

In my personal experience, yes. I wouldn't worry about it, especially if the magnet is clean. You should check your breather tubes though, if they aren't allowing air back in, temp changes can cause the grease to get sucked through the axle seals.

Yes that makes total sense... So I just went out and disconnected the front breather and blew on it. It passes air, but there was a pretty good amount of resistance. My Mity VAC is at my shop and I have never calibrated my mouth so I cant say exactly how much, but it took a while to get air through it. So is that box the breather goes in a filter of sorts? If so there should be some resistance right? I'm sure the pressure changes are slow so maybe its accommodative enough.

 

[IdahoDoug]

To be sure on that breather, I'd just use fuel line to extend it up into the engine bay. Zip tie the tip up high and pop an ordinary cheap inline fuel filter on it. On the axle end, it will fit right onto the nipple the factory hose uses. Now you'll never generate a vacuum in the diff and it's protected up higher.

That snorkel tip typically gets clogged, causes a vacuum in the diff housing each time you park and things cool and sucks a little grease into the diff housing. It's nothing to worry about as long as you're replacing the grease that normally weeps out the birfield sweep seals onto the spherical axle ends to keep the seal lubed by design, plus what you're losing into the diff.

DougM

 

[-Spike-]

Yes that makes total sense... So I just went out and disconnected the front breather and blew on it. It passes air, but there was a pretty good amount of resistance. My Mity VAC is at my shop and I have never calibrated my mouth so I cant say exactly how much, but it took a while to get air through it. So is that box the breather goes in a filter of sorts? If so there should be some resistance right? I'm sure the pressure changes are slow so maybe its accommodative enough.

That retarded thing is a check valve, throw it away and extend the lines like Doug suggested. The pressure change when you run a hot axle through a cold creek or puddle is probably faster than you might think.

 

[Tyler93]

Moly in the diff is common. I change my front diff gear oil every 6 months due to moly contamination. I have never done a front axle rebuild (owned 2 years) and my birfs don't click. I do add moly to the knuckle on occasion and I have no signs of birf soup.

 

[kidglove13]

If diff fluid is not leaking at the knuckles you are fine no need to tear it down again.
Moly in the diff is common.
Just change every few months and make sure the knucles have enough grease.
Nothing to worry about its all good.

 

[atomicshawn]

So I wish I had consulted you all with this issue months ago, worrying about whats going on in that front diff has given me an ulcer. Much thanks.

That retarded thing is a check valve, throw it away and extend the lines like Doug suggested. The pressure change when you run a hot axle through a cold creek or puddle is probably faster than you might think.

Again, perfect sense Spike. We do hit a puddle from time to time...

 

[atomicshawn]

So almost a year later here I noticed my wheel bearings were getting a little loose so yesterday tore down the hubs to pack em. I noticed the drivers side birf housing looked a little dry so while I had the hub apart I zipped off the spindle to take a peak...

So my little hypothesis that if the axle seal goes bad gear oil would likely end up in the birf housing before birf grease would end up in the axle fluid? Yeah, WRONG! The housing was almost dry. Over time it all must have migrated into the axle...

 

[lt1fire]

Yeah the heat from the diff sucks the grease the other way

 

[Tools R Us]

In my experience, it is normal for some grease to migrate into the axle and some to be lost past the wipers, etc, so it needs to be replenished through the plug to maintain proper level.

 

[atomicshawn]

In my experience, it is normal for some grease to migrate into the axle and some to be lost past the wipers, etc, so it needs to be replenished through the plug to maintain proper level.

I replaced the axle seal thanks to Kurt at Cruiser Outfitters who I think had the only 80 series front axle seal in Utah!... pretty fortunate to have that resource. Anyway, the seal was totally destroyed so I couldnt tell if it was damaged but I suspect it was, that seems like a lot of grease to be gone in 15-20k. But I think I'm going to take Tools' advice and make checking birf grease part of regular maintenance.

Hey Kevin, how do you check for proper grease level and how often?

 

[Tools R Us]

...
Hey Kevin, how do you check for proper grease level and how often?

The easy/quick way; look at the grease build up line on the ball, it is often thicker/heaver up to the grease level, much less higher up.

More accurate way; turn the steering all of the way towards the side that you are working on, remove the plug, using a flashlight look into the knuckle. If you can see the spindle bushing, etc, it is low.

The knuckle needs to have an air space, 1/2-3/4 full, not totally full. When filling it is difficult to tell how full it is, so I add, drive, check, repeat, until happy with the level. Most times, only add 1/4 tube of grease at a time.

I check/fill a couple of times a year. Most that I see consume ~1/4-1/2 tube a year, this depends on miles, how hard the rig is used, etc.

 

[kidglove13]

I have found that using a long zip tie as a dip stick works well also.