front axle diff breather - free advice

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Well, I've noticed quite a few posts of folks doing their birfs and thought I'd reiterate some sage advice many have posted about doing the differential breathers at the same time (or soon thereafter). I had been doing this on trucks for a long time based on the thoughts about sucking water and/or dust into the oem breather and fouling up the gear oil leading to some kind of bad consequence. On the 80, the first thing I noticed was that the plugged breather seemed to be responsible for my inner axle seals blowing and then leading to doing a full birf job just because of the two seals. I routed the breathers based on George Scolaro's website info, tying in the tranny and xfer case ones to one breather mounted up to the top of the DS firewall. I guess I always figured that the oem breather was just a crap design and got plugged from road dust etc.

Well, today I got to see what was probably the culprit and thought I'd pass along the experience to nudge those along that still haven't replaced the breathers after spending so much precious time and money doing the birfs. First, as above, the breather is extended using fuel line to a valve cover type breather (much like a little K&N) and the gear oil is all synthetic and filled to the FSM specs. I was working out in the Coachella Valley of southern CA (Palm Springs area) where the daytime highs are in the triple digits already. I had a full truck of gear and three big guys (all 200+). I had the A/C on high and was late so we were blasting on the I-10 somewhere north of 80 and south of 100. The truck is turbo'd w/315's and stock gears. Ran like this for about 2.5 hours. After stopping I went out later to run an errand and noticed the entire DS wheel well and pretty much everything under the hood on the DS was wet with something. I thought it must have been a power steering hose - nope. Kept looking and finally traced it back to the differential breather! So it probably was not more than half a quart of total loss - don't know haven't pulled the diff fill plug yet - but obviously with the front driveline always engaged it is possible to get the gear oil to move up three feet of tubing and out if you get it really, really hot. So maybe under less stress the oil just makes it to the oem breather and gets it gummed up and jammed. Enough hot runs and you toast your inner axle seals. Just a thought but I had a pretty convincing real world test that made me glad I had done the breather extensions. I'll drain the diffs and refill just to make sure I didn't miss anything. Hope this helps someone.
Cheers
Mike R
 

turbocruiser

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Very interesting information - I would expect some expansion of the oil but that is truly incredible. Makes my mind go to thought two : does tying the tranny/transfer into the diff breather perhaps possibly introduce gear oil into the tranny? That we would not want would we? Thoughts? Thanks again man, very interesting. :cheers:
 
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Yeah, I'm already second guessing having them all connected now after this experience. I guess maybe one step forward, two steps back - right?

I'll probably change out the tranny and xfer case just to start from a known condition.
 

Cruiserdrew

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Mike-That doesn't sound right. Even if thermal expansion made the diff oil expand in volume by 20%, It wouldn't come close to overfilling the axle and blowing out the breather. Something odd must be happening. Check the axle and see how underfilled it is, and I would look for something else happening. I recently ran 80 mph for 12 hours going to Moab and had no gear oil coming out the breathers. Now it was only 65 degrees, not 90 degrees but still the point remains. I would check to see of your 3rd member to axle bolts are tight, and if you somehow could have ingested significant water in your travels. Is the gear oil heavily contaminated with grease, causing it to foam, and the foam blew out the breather? There is no way that the thermal expansion alone (in reality 10% or less) could have caused this. I'll be interested to hear what you come up with.
 
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Thanks Andy. Yeah, I took a lot of physics too and can't believe it. So I'm out now trying to clean everything up and start the draining...just when I thought I'd have the time to do something fun!
 

turbocruiser

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Cruiserdrew said:
Mike-That doesn't sound right. Even if thermal expansion made the diff oil expand in volume by 20%, It wouldn't come close to overfilling the axle and blowing out the breather. Something odd must be happening. Check the axle and see how underfilled it is, and I would look for something else happening. I recently ran 80 mph for 12 hours going to Moab and had no gear oil coming out the breathers. Now it was only 65 degrees, not 90 degrees but still the point remains. I would check to see of your 3rd member to axle bolts are tight, and if you somehow could have ingested significant water in your travels. Is the gear oil heavily contaminated with grease, causing it to foam, and the foam blew out the breather? There is no way that the thermal expansion alone (in reality 10% or less) could have caused this. I'll be interested to hear what you come up with.

Well, theories will spring forth, i'm sure, and i'm hoping. Some things to think through in no order of importance.

First, for this to have happened does not necessarily mean that only the oil expanded so as to fill up the volume of the diff as well as the volume of the extended tubing. That measurement of potential volume seems so much greater than the actual volume of oil in the diff that on the surface it seems impossible to make the oil expand enough ... which is what you are saying if i'm reading you right drew, and which makes sense given how much the oil does expand with those typical temperatures (you can look those expansion rates up btw to really get accurate, or, just ask Cary, he's got em memorized most likely).

It could be that the oil gurgled with air up that tube over a period of time, or that the tube and filter combination served somehow as a small siphon and "encouraged" the fluid up, or that the end of the breather was somehow not allowing air in and that this along with negative pressure pulled grease from somewhere else, water from somewhere else, etc, effectively increasing the volume of fluid in the diff to then migrate up the tube???

Anyways, I dont have the answer just a lot of little thoughts about it but this is super cool and I would love to learn whatever comes of this. :cheers:
 

flintknapper

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Who knows.

The extended breather on my full size Bronco does the same thing (the rear one). I have it routed up to a spot along side the fuel filler cap, probably three and a half feet of line. I find small amounts of gear oil on the outside everytime I do any highway driving.

It is not thermal expansion that does it... IMOP. Not in the sense that fluid is expanding to that degree anyway.

I believe that gear oil or (tranny fluid) is being splashed around enough to form a bubble at the bottom of the tube and then increasingly heated and expanding air is forcing it up the tube and out the opening. NOT FLUID.

I think this occurs over and over in small amounts until the diff. reaches a point where it is no longer getting any hotter and it quits.

You have all seen a bubble of air pushing brake fluid ahead of it when bleeding brakes. I think the same thing is happening sometimes with open ended breathers.



EDIT: O.K. looks like turbocruiser beat me to it. I agree however.
 
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ok, a little more info. One thing I failed to remember and mention is that since I did the turbo, and it wasn't a "real" US-spec Safari unit, I had to source my own tranny oil cooler. I went with the oem mazda rx-7 turbo oil cooler - which just happens to have its own thermostat. I can hear a collective "Ahhhhhh". So I'm pretty sure if it was stuck this would jack the pressure up enough to force out some through the breather. I was a bit suspicious of this since I was able to get my "A/T" light to come on back in March on the DV trip.

Second ok, the fluid was tranny fluid not the diff gear oil. It was harder to tell for me with the sun setting now but I confirmed it. So I'm moving on to draining and refilling the tranny fluid first and pulling and replacing the mazda cooler t-stat first. I'll go ahead and separate the breather lines too since it still sounds like there could be some cross-contamination.

Thanks for all the input. It really helps to get several points of view on what to check/ look for while trying to keep the truck tight. BTW, no lights or gauges or complaints so I'm pretty happy with that!

I realized that every post should have a pic - some "on the job hazards" are different than others!
 

Cruiserdrew

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Cool-that makes a lot more sense. There are almost 4 gallons of tranny fluid to heat up and not much extra space. Does the trany fluid look brownish like it got really hot? It sounds like you need a new tranny cooler for sure. Good luck.
 

MaddBaggins

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Speaking of breathers, I traced my xfer case and tranny breather and found that they both go over and into the tranny dipstick tube. I followed them with my hand while lying under the truck. I couldn't find anything defintive in the FSM on where they are routed.
Is this a stock config? If thats where they run to I feel pretty comfortable about their stock height.
I have already extended my diff breathers. :cheers:
 
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yes, check here (http://george4wd.taskled.com/breather.html)

MaddBaggins said:
Speaking of breathers, I traced my xfer case and tranny breather and found that they both go over and into the tranny dipstick tube. I followed them with my hand while lying under the truck. I couldn't find anything defintive in the FSM on where they are routed.
Is this a stock config? If thats where they run to I feel pretty comfortable about their stock height.
I have already extended my diff breathers. :cheers:
 

LandCruiserPhil

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Clown where do you have your new A/T cooler mounted and does it also run thru the bottom of the radiator? Is there any air flow to the cooler besides the fan? IIRC the light comes on around 230 degrees hot enough to burn normal A/T fluid. I asked about the A/T light coming on before and only a couple poster replied and they where very heavy or towing. I'm wondering why or how your A/T got so hot?
 
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Phil, it is mounted just below the intercooler and does still incorporate the resevoir at the bottom of the radiator. Air flow is not optimial and I've been scheming to place a small temp controlled elec fan or pair of them on it to increase flow. Strangely though the only two times I've ever gotten my AT light to come on is in DV! Last year I did it with the SC on and was really rallying hard up Pleasant Canyon trying to catch up to the group. I had just driven pretty agressively from Riverside to Ballarat without stopping and then continued up Pleasant Canyon. I did engage the CDL once I hit snow and that's when the AT light came on. I stopped and it was pretty toasty under the hood. Second time was this year with the current turbo setup. I really think it's the t-stat on the mazda unit but am replacing it today so will know more. I spoke with Andy and others at DV about this and not a single person had ever had the AT light come on, so I'm pretty interested in what I'm cooking in there..
 
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