Front Diff fluid leak - probably CV seals but not sure yet

[kcjaz]

So last week, I finally had time to get back to the 200 to get her ready for the season (Moab will be here before I know it) and found oil on the floor by the drivers wheel. Took off the skids and found this:

So I cleaned it up and let her sit a week and found this:


As I was recording the video, the leak running down from the CV wasn’t as obvious as the video shows. Maybe I should always record videos when looking for leaks…

I cleaned it some more with degreaser and used a heat gun to dry it before I take it out to run it a bit to see how bad the leak really is. When I did that I found this:



I wouldn’t think that front diff support mounting bolt would need to be sealed or could be a potential source of leakage but maybe the bolt hole goes through? Nah, no way. I’m guessing it’s just residual oil that collected while the leaking oil was being slinger around. FSM says 114 ft-lb so I’ll check it. Maybe remove and reinstall the bolt to better see what’s going on.

I’m going to check the level and top off to see how much fluid I’ve really lost, then go for a drive…

Edit: those bolts do go through so they could be the source of a leak if loose or the sealant was bad or both. All three bolts were nowhere near 114 ft-lb so I think I found part of the problem.

 

[kcjaz]

Just check gear oil level. Added 230 ml of oil to see fluid at the drain plug. Capacity is 1.9 l so not catastrophic but could have been if not found for much longer. I think this started at COTR in Tennessee in October. I drove home and the 200’s been parked since. Going for a drive now.

 

[kcjaz]

Went for a drive on highway and then put her through the paces in 4lo, CDL locked unlocked, front/rear lockers on and off. Goet back home, put her on the lift and:

Clearly, the diff connection on the driver side and a small drip on the passenger. The diff mount bolts don’t seem to be leaking anymore.

 

[kcjaz]

Pulled the drivers CV today. First time for me most of the afternoon. Had a hard time getting it out of the front diff. A little PB Blaster and figuring out I didn’t really need to worry about the tin dust cover as it just pulls loose when the axle pulls out. This video was very helpful:



Hub was super clean:

Supported hub with ratchet strap hooked to compressor bracket:

Block of wood:

Tools needed:

CV seems to be in good shape:

 

[kcjaz]

I pulled the seal and cleaned it up. It seems perfect. I did find a small piece of what I at first thought was metal but it wasn’t magnetic and I was able to easily cut in in half with my pocket knife. My theory is that this small piece of clay/rock got in under the seal somehow and caused the leak. I am blaming this all on Tennessee. I also found a spot on the face of the axle hole that is scratched and there are some other scratched on the face that would be under the seal. Not sure if this is something to be worried about or not. The pic makes it look like the edge of the face may be nicked but when I run my finger around the seating circumfrence it’s smooth.

 

[kcjaz]

I was looking harder at the seal I pulled out and found this:

My guess is that this part of the seal was at the scratched part of the face (pictured above). I’ll replace the seal but now I’m worried that the scratched area on the axle hole face may cause damage to the new seal and it will leak again. I’ll try installing the original seal (at a different clocked position) and then pull it out again to see if it gets scratched when installed. I don’t see any reasonable way to fix the scratches on the axle hole other than maybe some very light sanding to debur it.

 

[bloc]

Has this thing been regeared? If so, by who?

In the pic of the CV it hasn't been cleaned yet.. I assume you did and the sealing surface there (the larger diameter just this side of the dust seal) is perfect? No nicks?

 

[kcjaz]

Has this thing been regeared? If so, by who?

In the pic of the CV it hasn't been cleaned yet.. I assume you did and the sealing surface there (the larger diameter just this side of the dust seal) is perfect? No nicks?

Yes, years ago. We also moved the diff from my old truck to my new one. It certainly could have been mucked up then.

 

[kcjaz]

The diff swap was done in Nov of 2023 so it’s run for 2 years.

 

[bloc]

I don't see how that damage to the housing could happen with the seal installed, whether from offroading or moving the diff from one to the other. Now while it was all apart for the gear install?

As for why it would leak now.. if the seal wasn't installed perfectly flat it can take a while for the interface between it and the CV to cause problems.

I know the seals aren't super cheap but I'd throw a new one in to full depth and see what happens. Again, assuming the sealing surface of the CV is perfect.

 

[kcjaz]

I don't see how that damage to the housing could happen with the seal installed, whether from offroading or moving the diff from one to the other. Now while it was all apart for the gear install?

As for why it would leak now.. if the seal wasn't installed perfectly flat it can take a while for the interface between it and the CV to cause problems.

I know the seals aren't super cheap but I'd throw a new one in to full depth and see what happens. Again, assuming the sealing surface of the CV is perfect.

I think I’ll use some gasket shellac on the seal when I put the new one in. I agree the damage doesn’t seem like it occurred wheeling. Something hit the metal part while swapping CVs around. Then I think the seal was scratched during install. It may have been leaking for a while just very slowly and I didn’t notice. The big leak was the three mounting bolts on the support bracket. Hopefully the re-torque will solve that.

 

[bloc]

I think I’ll use some gasket shellac on the seal when I put the new one in. I agree the damage doesn’t seem like it occurred wheeling. Something hit the metal part while swapping CVs around. Then I think the seal was scratched during install. It may have been leaking for a while just very slowly and I didn’t notice. The big leak was the three mounting bolts on the support bracket. Hopefully the re-torque will solve that.

Sounds like a good plan.

 

[kcjaz]

Cleaned up the diff and inspected it throughly. It’s seems to be in good shape for 183K miles and a lot of off road. I did notice some slight “scaring” on the sealing surface that you can feel with your finger. I tried measuring where the seal would be on my spare CV and compared it to the markers on the old one. I think the “scaring” or ring is inset a bit. Perhaps the seal was set in too far. O should have noted the depth before I pulled the seal out.

 

[bloc]

You may be able to use the calipers to measure the seal position in the diff case based on where that shoulder on the CV sits.. then check seal position.

 

[kcjaz]

You may be able to use the calipers to measure the seal position in the diff case based on where that shoulder on the CV sits.. then check seal position.

Good idea. I’m a bit worried about the scratches on the axle causing a leak if that is where the seal rides. I guess I’ll find out. FSM provides the depths:

The FSM is a bit confusing when it says “tap out the 2 oil seals”. I believe they just mean left and right sides as there is only one seal per side.

 

[bloc]

I believe they just mean left and right sides as there is only one seal per side.

That would be my read as well.

 

[kcjaz]

That would be my read as well.

Hey, any reason to replace the hub side seals? They look fine so I wasn’t planning on it but order a pair just to have in case I find something unexpected on the other side when I pull the axle.

 

[bloc]

Hey, any reason to replace the hub side seals? They look fine so I wasn’t planning on it but order a pair just to have in case I find something unexpected on the other side when I pull the axle.

I planned to do mine whenever I throw in CVs.. but they are mostly holding dirt/grime out of the bearings vs holding fluid into the diff.. so their seal doesn't need to be quite as air tight.

 

[UPR LC]

Good idea. I’m a bit worried about the scratches on the axle causing a leak if that is where the seal rides. I guess I’ll find out. FSM provides the depths:
View attachment 4091659
The FSM is a bit confusing when it says “tap out the 2 oil seals”. I believe they just mean left and right sides as there is only one seal per side.

Can you buff out the area where the seal rides on the axle/CV with some scotchbrite pads or steel wool? I wouldn't think you would hurt anything by doing so, and it is more likely to prolong the life of the seal. Would be worth doing to extend seal life since removing axles is not the easiest/quickest job.

I would do the same for the area of the diff housing that was damaged (dented and scuffed).

 

[kcjaz]

Hope to get back to the 200 this week end and reinstall the CV I pulled. Looks straight forward:

I tried getting new snap rings but they didn’t show up in my parts order. Since I’m not trying to remove them risking breaking or bending them, they should be fine to reuse. I’m not 100% sure what “hypoid” gear oil is Googling that I believe is just the 75W-90 gear oil I use in the diff.