Differential Leak

Went to change my differential and noticed the lower half looks wet. Also, on the inside (top) of the heavy skidplate, I can see where the fluid has been puddling.

Is it as simple as taking the cover off and replacing the gasket? Or will I have to take a bunch of other stuff off?

Not sure how to scale down the images.

 

How does gear oil corrode your skids plate?

 

My bad. I took a screw driver and scraped the skidplate and it was just a pile up of dried gear oil that had the perfect texture of rotting metal. That one had me perplexed too. I need more sleep.

 

That looks like the front diff, correct? If so, it's likely the axle seals that are leaking and not the clamshell itself. If it's the clamshell, you have to pull the whole diff out to separate and reseal it. PITA to do.

 

FML, I was afraid of that.

Saw a vid on how to do that and don't think I could do in the garage. May have to end up having to pay a mechanic.

 

Start with replacing the axle seals. You don't have to drop the diff to do those, just pull the axles out. Not hard but it will take some work. Be a good time to replace the CV boots as well if they look iffy.

 

Looking at those pics again, it actually looks like the drain plug might have been seeping, which would also leave the diff looking wet. Make sure you use a new seal for the plug when you reinstall it. They are all over on Amazon for cheap.

 

Thanks guys. @xtremewlr I didn't think of that. I will try wiping down the front differential today to get the gear oil off, so I can see if it's a leak or not. If it's a leak, I will try the axel seal replacements.

I changed the fluid in the rear differential, front differential, and transfer case. Used 75W-90 Mobil 1.

I used all new washers from this kit on Amazon.
https://www.amazon.com/dp/B08K8S3B2D

For reference 4th gen 4Runner part numbers for crush washers and fill/drain plugs (from link above)

Transfer Case Fill Gasket 90430-18008
Transfer Case Drain Gasket 90430-18008
Front Differential Fill Gasket 12157-10010
Front Differential Drain Gasket 90430-24003
Rear Differential Fill Gasket 12157-10010
Rear Differential Drain Gasket 12157-10010

Transfer Case Drain Plug 90341-18006
Transfer Case Fill Plug 90341-18006
Transfer Case Breather Plug 90930-03172
Rear Differential Drain Plug 90341-18057
Rear Differential Fill Plug 90341-18006
Rear Differential Breather Plug 90930-03031
Front Differential Drain Plug 90341-24014
Front Differential Fill Plug 90341-18032
Front Differential Breather Plug 90930-03136
Oil Pan Drain Plug 90341-12012
Oil Pan Drain Plug Gasket 90430-12031

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4th gen 4Runner Torque and Fill specifications

Front Differential
Drain Plug - 10mm hex bit, 48 ft/lbs
Fill Plug - 10mm hex bit, 29 ft/lbs
Fill quantity - 1.5 qts

Rear Differential
Drain Plug - 24mm socket, 36 ft/lbs
Fill Plug - 24mm socket, 36 ft/lbs
Fill quantity - 3+ qts

Transfer Case
Drain Plug - 24mm socket, 27 ft/lbs
Fill Plug - 24mm socket, 27 ft/lbs
Fill quantity - 1.5 qts


In my poorly lit workspace (garage, at night), I didn't notice the wet looking front differential until the next day when I went back under to inspect my CV axels more closely, which badly need replacing.

Both inner boots are leaking with grease all over the place, but not torn. So the CV axels are next. I'm going to have to buy a lift and jack stands for that.

 

I wouldn't replace the CV axles, just reboot them. Especially if they are still OEM CVs. Aftermarket CVs are not nearly as good as OEM and even with leaking or torn boots, they are likely not bad and just needs new boots and grease. Boot kits come with new grease and rebooting would save you a ton of money over replacement axles.

Spray the diff down with brake cleaner and call it good. Give it a while/couple hundred miles and then check to see if the front diff looks wet again. If you are doing CVs, you can replace the axle seals at the same time.

 

Going to buy some brake cleaner today to spray the front differential.

Took a few more pics.

Skid plate where the front differential oil had leaked on it.




Drive shaft going to front differential.





Front Differential fill plug, is it supposed to stick out that far when tightened to torque spec and using new factory crush washer? Never noticed it sticking out that far.

 

As long as the fill and drain plugs tighten down to torque spec with the new washers on them, don't worry about it. Hose the diff down good with brake cleaner and check for leaks after a few hundred miles.

 

CV axel inner boot, drivers side leaking.







CV axel inner boot, passenger side leaking.

 

Yeah, replace the boots, not the axles. Those are for sure OEM and are far better than aftermarket. That is a minor leak on each of them, so the CV joints will be fine still.

 

This is great to know. Thanks for all your help and knowledge. Really appreciate it!

 

Both inner boots on my 2003 V8 were torn when I bought it. So probably for quite a while. Replaced the boots and I'm still running those axles without issues. I've put close to 60k miles on the truck since I bought it.



You can get replacement boots cheap that come with fresh grease and the clamps needed. You just have to get a crimping tool for the clamps which you can find on Amazon.

https://www.offroadsolutions.com/products/replacement-cv-boot/
https://www.amazon.com/s?k=cv+boot+crimping+tool&crid=28E9Z3AIEPSP1&sprefix=cv+boot+crimping+tool

I used the orange, high angle boots from OffRoadSolutions since my truck is now lifted but the standard boots will work fine for your application up to 2" of lift or so.