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Rear Diff oil, should it look like this?


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This is my 1st time changing the rear diff oil.  I had a local shop change it in the spring before a big trip and they said it was 'very nasty'.  I just assumed the PO had not changed it in a while. 

So, after 8-9 months and ~11k miles, is this normal?  Or is there something else going on I need to be concerned with?  Oh, and the smell!  It was nearly vomit inducing.

IMG_2085 - Copy.jpg

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That is the colour diff oil often looks like when it has been running with water in the oil. That make you want to vomit sulfur smell is not uncommon among diff oils and the strength of it depends a lot on the type and manufacturer of the oil and gets stronger the longer the oil is run. More common among dino oils than synthetic.

Edited by saddlebum
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I agree, most oil has a milky look if it has some water present. I'd change it with a quality oil that meets the spec, carry on, and change it again after maybe 2 oil changes. Too cheap and too easy.  Did you find any signs of metal shavings?  Who knows, local shop could have been using old opened oil that added to the problem. 

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Chocolate milk oil like that is almost always water in the oil. Diff oil just stinks, even the new fresh bottle stinks.

I would change that out and change again after 1 full tank of gas, and keep doing changes after each tank of gas until all that nasty stuff has been flushed out. After that I would keep a close eye on the oil after a run in the rain or washing it, you may have a bad seal that is letting water in. You will need to get that fixed if you do or gear and bearing damage WILL happen.

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I would want to know how water got into it. Bad seals are often the cause. High pressure washing can force water in past the seals since the seals are designed to to keep oil in not water under high pressure out. The same holds true if you ever submerged the axle in water wear the axle seal or the vent is under water.

Edited by saddlebum
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Ah, that makes sense.  I'm planning to take it to the local dealer in January to get it ready for some 2022 travels.  I have a list of things for them to look at/do, so will add that to the list.

It hasn't seen much of any rain at all, just a couple of light rains (I was lucky), but I have been to the carwash with it a couple of times.  I'm always careful to stay back quite a ways with the pressure hose, but perhaps not careful enough.

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Hey Guys,  While I never underestimate my ability to do stupid shtuff, I have always been aware of the damage high pressure washers can do and know to be super careful.  I was just out looking @ my Venture to see how/where I could have gotten water into the rear diff while washing.

I'm scratching my head, because even if I wanted to, it sure looks like I would have to try pretty hard to even hit any part of the rear diff directly with a blast of high pressure water.  So, I went to the exploded view dwg on partzilla (attached) to see where the vulnerable areas are and now have a couple more questions.

1) What is item #23, the 'breather'?  Is that a possible point for water entry?

2) I have never pulled the rear wheel myself, so unsure of what that entails, but I've had a small local independent shop do two rear tire changes for me.  Not sure how to ask this, but is there an opportunity to not get something put back together correctly that would create an opening for water to get in?  Perhaps via the axle or leaving out an o-ring, seal or possibly pinching one of those?

Other than doing another gear oil change in a few hundred miles to see how it looks, I won't be digging into fixing any potential problems here but will leave that to my local dealer techs, if need be.  Just trying to educate myself on possible causes so as to have a semi-intelligent conversation with them when that time comes.

Thanks, so appreciative for all the knowledge here.

diff.jpg

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The breather is a possibility, it allows air to escape when the pumpkin heats up and then allows air back in when it cools down. If it weren't for the breather then air would be transferred past the seals , and that would spoil the seals with contaminates. The breather should have a filter in it to prevent any contamination, but it may be compromised. It may be plugged, but then I would suspect to see some oil residue around the seal areas.

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6 hours ago, Marcarl said:

The breather is a possibility, it allows air to escape when the pumpkin heats up and then allows air back in when it cools down. If it weren't for the breather then air would be transferred past the seals , and that would spoil the seals with contaminates. The breather should have a filter in it to prevent any contamination, but it may be compromised. It may be plugged, but then I would suspect to see some oil residue around the seal areas.

This also is a very good point. To add to it, when the diff cannot breath air gets drawn in through the seal but cannot escape. As the diff warms up and since the seal will not allow the air to escape pressure builds up in the diff compressing the moisture in the air to convert to water. As the diff cools a negative pressure forms in the diff allowing more air to enter the diff. further cooling depending on how much can cause condensation to add further to the water build up in the diff. As this cycle continues the water content in the diff builds and eventually you get enough water contamination to turn the oil into that tasty looking light fudge color (But Don't be tempted to sample it). After awhile if left long enough you will get a seal failure and you will see signs of oil leakage.

Some years back Rockwell decided to install breathers in their truck diffs that were a third the size of what they used to be and because they were so small they would plug up with dirt and as a result we had numerous trucks coming in with the above mentioned issue all coming in with early wheel seal failures and that lovely brown liquid fudge. We eventually figured out the cause was that these undersized breathers were plugging up cause the scenario I also described above. Since the hole was too small to go back to the larger breather and drilling and tapping was out of the question due to warranty we started replacing the Rockwell breathers with the J tube style breather that Eaton used on their diffs. and the problem was solved. It was so prevalent that eventually Rockwell's warranty fix for this issue was to use the Eaton breathers. Following rear ends went back to the larger breathers and the issue disappeared. 

Edited by saddlebum
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4 hours ago, circa1968 said:

@Marcarl @saddlebum I just renewed my membership last month and you guys are making me feel guilty as I've already gotten more than my $12 worth here!  Thank you!  The knowledge...I appreciate you guys!

Your Welcome but it if were not for the founder of this site and the members of the site the knowledge possessed by those members on this site that have it would not be able to share it with those that have need of it.

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2 hours ago, saddlebum said:

Your Welcome but it if were not for the founder of this site and the members of the site the knowledge possessed by those members on this site that have it would not be able to share it with those that have need of it.

Are you confirming that we are possessed?

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I would suspect the vent is where your getting water in. There probably at one time a piece of foam like material in it to keep crap out like dirt. They have a tendancy to deteriorate over time and then its pretty much free flow. If it does not vent, they build pressure and will blow out the seals. If you are not showing any drips, I would say the seal is OK. Depending on how old the fluid is, it could be just old and moisture gets trapped in there over time and fluid will look like that. Run some dino gear lube for a few hundred miles or more. I think I would go maybe at least 500 and drain a little and see what some looks like drained in a solo cup or something. Once you get a good sample put some synthetic in it and let er rip.

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@djh3 @saddlebum @Marcarl  Thanks guys!   I will report back in a few hundred miles.  In the mean time, I looked up the breather and its only ~$14 on partzilla, so maybe worthwhile just changing it as a precaution anyways.  

But its a perfectly round and smooth chrome knob.  Any idea how one goes about getting that sucker off and a new one back on?  More on the re-install, I can gorilla the old one off, I'm sure.

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On 11/28/2021 at 7:10 AM, N3FOL said:

Did you ever cross a small river or crossed a flooded road?  Just throwing out possibilities. 

No, nothing like that, a little bit of light rain while riding but that's it.  I suspect the water was most likely drawn in through the breather as it was cooling down - and I was washing the bike.   I would give the bike a good 15-20 minutes of cooling down before washing, but perhaps that is not enough.

I was also in the midwest during some hot/humid days, so that is another possibility for drawing in moisture while cooling down after a ride.

I will probably just change it with each oil change from now on.  Its easy and inexpensive.  I would like to change the breather too, as a precaution.  Will report back if I can figure out how to remove it.

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