Rear differential leaks

TMCINTOSH11

MEMBER
2002 DODGE RAM
4.7L
V8
4WD
AUTOMATIC
275,000 MILES

Hi, I'm not new to differentials but I'm also not really too experienced with them either.
On my truck I noticed a while back there was a drop of oil hanging on to the edge of the driveshaft u-joint and saw were oil had been flown all through the underside of the bed so I figured the pinion seal is starting to go bad. I hadn't messed with differentials in a while but I thought I'd see if it needed fluid so I got the recommended fluid type from the dealership and starting adding some to it. I know this may be wrong but I was taught to add oil until it started oozing out and then it was full, so that's what I did.
So shortly after I looked under the truck one day and noticed some type of fluid that splashed all over the inner side of the rear driver side tire and a drip from the heat shield on the hub, I thought it was brake fluid but the hoses were bone dry and so was the caliper, so I got some on my finger and sniffed it and it was differential oil.
So with this information I started researching online but I didn't see much of what it was except a possible axle seal leak, then I came across a forum that said that overfilling the pumpkin can lead to the breather being unable to vent any pressure and cause fluid to go either one side or the other, he said it's going to go somewhere.
So far there isn't any performance issues or even the slightest noise coming from the rear differential, I been driving it this way and I'll have the pinion seal fixed here shortly, but should I be worried about the axle leak or could it be because of too much fluid? From now on I'm going to check the fluid first with my finger before I put anymore in.
Thanks!

6 Replies

KASEKENNY

MECHANIC
18,907 POSTS

This is part of the problem with forums is they are misleading in most cases because they don't give enough detail to know if it is the same as what you have.

They are correct that if you overfill a differential then it can cause these venting issues. However, what they are saying is if you fill the diff from the vent hole with the fill plug installed and you fill it past the fill plug and basically fill the case with fluid. This will cause it to push the fluid out the axle tubes and leak all over the hubs and brakes.

Also, you are correct on how to fill this. You pull the plug and when it runs out, you put the plug back in.

https://www.youtube.com/watch?v=v6PjkozhrAc

What I would suggest is start with what you know is leaking. Replace the pinion seal and then clean the entire undercarriage with a degreaser and hose and then recheck it every other day to see if there is any new fluid.

Here is the process from the manual that will help with this. Please let us know if you have other questions. Thanks

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Saturday, April 17th, 2021 AT 5:35 PM

TMCINTOSH11

MEMBER
176 POSTS

Thanks Kenny,

Yeah, the forum was referring to filling it the same way I was, they said it's supposed to be filled to just below the fill hole but I'm going to take your advice instead because I was always told that's how it's filled anyway.
Thank you for the information on the pinion seal replacement, I'll have it done soon and let you know how it goes.
I checked the fluid with my pinky finger yesterday and it was completely submerged in fluid so I know it not going anywhere quick.

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Sunday, April 18th, 2021 AT 4:37 AM

DANNY L

MECHANIC
5,648 POSTS

Hello, I'm Danny.

Just here to add. You added differential gear oil the correct way. When you remove the fill plug and add oil and it starts oozing out (vehicle being level) that is the correct way. Before replacing the pinion seal which is costly I would use a good strong degreaser and clean the underside of the bed and the differential assembly including the brake backing plates to verify the leak before having the pinion seal replaced. Pinion seal replacement is costly so I would double check the leak first. Also, If the axle seals are leaking you might want to pull off a rear rotor or brake drum (depending which brake option) to see if the parking brake shoes (Disc) or brake shoes (Drum) are contaminated with the gear oil. If contaminated the rear brakes will need to be replaced. Hope this helps and thanks again for using 2CarPros.

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Sunday, April 18th, 2021 AT 5:23 AM

TMCINTOSH11

MEMBER
176 POSTS

Thanks Danny,

I guess I can't say how long either leak has been occurring, the first one I noticed was the pinion seal because I happened to notice a small amount under the rear end, it was only about the size of a half dollar coin, and I saw a drop hanging on the bottom of the driveshaft u-joint. So afterwards I decided to just get some differential oil and start filling it, it took a full quart before it was full, then when I went to check the fluid about a week later I noticed what's in the picture, so I don't know if this had just started happening or if it's been ongoing. So far now I haven't had to put any more oil in it for a good minute, I use my pinky finger to check the level and each time it completely submerged in oil in it. I'm going to check it again tomorrow or next day.
I guess now my questions are which should I replace first? And is the pinion seal causing the axle to leak?
And based on the picture what is the severity of the leak?
Thank you so much for all your help!

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Tuesday, April 20th, 2021 AT 5:31 PM

KASEKENNY

MECHANIC
18,907 POSTS

That is a pretty substantial leak. I doubt the pinion is causing the axle to leak so if it were me, I would replace them both. However, if you are going to start with one, then start with the pinion.

Let us know what other info you need.