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leaky rear differential vent tube

cerberusaardvark

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1994 Explorer xlt
I've got a 94 with a 97 rear end disc conversion and lsd. I also have a solid diff cover that claims it can hold an extra quart inside. Since the two years I've put it in, the vent tube continues to leak disgusting stinky diff fluid. It's a very slow rate.. maybe a couple drops a day. I tried extending the vent tube up above the spare tire hangar and lengthened it by aabout inches but it still leaks.

Can I put a check valve inline or just straight up seal it off?
 



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Does the vent tube leak from the end of the hose, or around the other end, at the metal fitting on the axle?

If it's 'leaking' out the end of the hose even when it's up around the spare tire, then it's probably from vapors that are condensing. That's probably either from water in the axle, or perhaps it's a poor quality gear oil. If it's a limited slip, you might want to be extra sure that friction modifier is used.

The transfer case vent hoses on Explorers come with a cap on the end to prevent debris from getting in there, so you might try to grab one from a junkyard Explorer and use that on the axle vent hose.

If it's just seeping around the axle end where the hose attaches, get a new hose clamp to attach it, the old one might be getting weak and not sealing. You can also use some grease between the hose and fitting to make a seal, or clean it up and then use some black silicone to make an oil-tight seal.


DON'T just 'seal it off' - axles are vented because they build up heat and pressure - if you seal it, heat will build up pressure, and it's going to blow something, either the seals on the ends of the axle, the diff cover, or the pinion.
 






jd4242

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May be a stupid question but did you still fill it up to the stock fill hole?? You didnt add an additional qt after it started coming out the hole right?? It shouldn't leak gear oil out the vent tube..small vapor or water/oil mix drops but thats even rare. .I think its over filled..
 












Maniak

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Yup, overfilled.
The cover will hold more fluid but not that much more [MENTION=62]Maniak[/MENTION] has a post somewhere on here about it.

Umm... yea.. I wasn't thinking that day.....

I kept adding fluid using the new fill hole in the new cover not realizing that the hole was higher than the axle tubes... I ended up with more than 2 quarts too much in there.... Lots of fluid ended up in the axle tubes...

~Mark
 






cerberusaardvark

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yes its coming out of the end of the tube... and it been doing that for two years and whenever i stick my finger in the new fill hole in the cover i still feel the level. i figured it would just reach an equilibrium eventually but i guess not. i used a 75 140 gear oil... even made a post on here a few months back about whether it was ok or not or to use friction modifier or not. the consensus was that it should be fine. im not adverse to draining it and filling back up with some synthetic formula and adding the modifier.

so even if the new diff cover has a hole that is higher than the old one for the purpose of holding more fluid to help with cooling i should continue to use the old hole as a fluid level indicator??

at this point my spare tire is soaked and im super over leaking from the back
 






jd4242

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yes its coming out of the end of the tube... and it been doing that for two years and whenever i stick my finger in the new fill hole in the cover i still feel the level. i figured it would just reach an equilibrium eventually but i guess not. i used a 75 140 gear oil... even made a post on here a few months back about whether it was ok or not or to use friction modifier or not. the consensus was that it should be fine. im not adverse to draining it and filling back up with some synthetic formula and adding the modifier.

so even if the new diff cover has a hole that is higher than the old one for the purpose of holding more fluid to help with cooling i should continue to use the old hole as a fluid level indicator??

at this point my spare tire is soaked and im super over leaking from the back

Yes use old fill hole..only way to get extra fluid in is if the cover is larger, sticks out farther. .not because it has a hole higher than stock, stock fill hole should always be used.it allows air space in the tubes for gasses to escape through the vent
 






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The covers that 'hold more fluid' hold more fluid in the differential because they allow more volume. The higher fill hole shouldn't be used as a level indicator since that puts more fluid in by overfilling.

So yeah, use the factory hole as the indicator, or mark the diff cover just below the factory fill hole so you can fill it from the rear.

You could probably just use a vacuum pump or syringe with some plastic tubing and remove some of the fluid that way, rather than a complete drain and refill if the gear oil is still good.
 






jd4242

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The covers that 'hold more fluid' hold more fluid in the differential because they allow more volume. The higher fill hole shouldn't be used as a level indicator since that puts more fluid in by overfilling.

So yeah, use the factory hole as the indicator, or mark the diff cover just below the factory fill hole so you can fill it from the rear.

You could probably just use a vacuum pump or syringe with some plastic tubing and remove some of the fluid that way, rather than a complete drain and refill if the gear oil is still good.

Why not just pull the stock plug out and let whatever drains, drain out????:scratch: No need for syringe or complete change..
 






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Why not just pull the stock plug out and let whatever drains, drain out???? No need for syringe or complete change..

Because the stock plug can be a PITA to remove and get to compared to a plug that's on the rear cover, and just letting gear oil spill all over the differrential will make for a real mess.

Sucking gear oil out of the cover filler hole seems like the easiest, cleanest method to me. Less mess, less work.
 






Maniak

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I guess I'm spoiled.... I can easily get to and take out the factory fill plug on our explorer. I don't even have to use a jack...

On the Mustang (also has an 8.8 solid axle) I just use jack stands and hold it up by the frame (well, what constitutes the frame on the mustang) and let the axle droop. Now I can easily get to the drain plug...

Also, we don't have rust here so I'm sure that helps....

As for the mess.. I just put a drain pan under it, and if I had to remove what I over filled I'd just put a pan under it, open the plug let it drain, put the plug back in and spray it with brake cleaner..

~Mark

Edit: It just occured to me.. I don't know if pulling it out of the factory fill will work though.. If you over fill it by quite a bit, then drive you will have quite a bit in the axle tubes.. That means it isn't in the diff itself...
 






jd4242

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Because the stock plug can be a PITA to remove and get to compared to a plug that's on the rear cover, and just letting gear oil spill all over the differrential will make for a real mess.

Sucking gear oil out of the cover filler hole seems like the easiest, cleanest method to me. Less mess, less work.

Personally that sounds a WHOLE lot harder..first I gota find a pump, second you know how hard it is to suck or pump rear end fluid.third it would be a guessing game to what level to leave it at and last you need to clean the pump and everything else you used...pulling a plug seems MUCH easier to me..
 






4x4junkie

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I've had this issue with the '99 axle I have under my BII.

On mine, the problem is the vent connection is not at the very top of the tube, it's down a bit toward the rear. Combine this with a bit of pinion uptilt for keeping the angle correct and it turns into a hard-to-win battle without running the axle dangerously low on fluid.

Not wanting to drill a new hole and risk metal shavings falling into the axle, my solution was a small canister as a reservoir inline with the vent hose mounted vertically up near the framerail (homemade from four inches of 1" copper pipe + two caps with 3/8" brass barbs soldered into them). This catches whatever fluid comes out and holds it there until the axle cools down then it simply drains back down into the axle.
 






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