Synthetic Gear Oil Too Thin For Axle Gears/Seals?! Front Diff Is Leaking...

midwestdenaliguy · January 9, 2023

Noticed my front passenger side axle is leaking oil. 2016 Sierra with 170k miles. I don’t have any grinding noises and the leaking oil is clear (changed it 20k miles ago). Figured it's probably time to replace the seal. So I called a couple differential/transmission shops near me to quote replacing the seal and one said to first swap the synthetic oil I put in the differentials with conventional and see if that stops the leak. He claims synthetic oil is too thin for axle seals with higher mileage and it seeps through them, plus is doesn't stick to the internals the way it should. Is there any validity to that? What doesn't make sense to me is that I've ran full synthetic in the front/rear diffs and transfer case for over 80k miles now (with one change in there) without any leaking until now. Should I switch to dino oil or go to another shop that will replace the seal?

Edited January 9, 2023 by midwestdenaliguy

rav3 · January 9, 2023

Before you do that, which I don't think is correct, put about 2 Oz of At-205 sealer in it & see iff it doesn't fix ur leaking. I just did this a couple months ago on wife's SUV on rear diff. It started leaking after I changed the GL5 oil (75W90) Red Line in it. I squirtted about an Oz. Of AT205 in diff. Case & it stopped the leak within a week. Good stuff. It softens & swells seals.

midwestdenaliguy · January 9, 2023

20 minutes ago, rav3 said:

Before you do that, which I don't think is correct, put about 2 Oz of At-205 sealer in it & see iff it doesn't fix ur leaking. I just did this a couple months ago on wife's SUV on rear diff. It started leaking after I changed the GL5 oil (75W90) Red Line in it. I squirtted about an Oz. Of AT205 in diff. Case & it stopped the leak within a week. Good stuff. It softens & swells seals.

Cool, thanks for the suggestion. Did you top off the diff with oil first then add an ounce of the sealant?

rav3 · January 9, 2023

No, it was a little low when I removed the fill plug, so I added 1 Oz because my diff only held about a quart & then top it off.

steelerdude15 · January 9, 2023

1 hour ago, midwestdenaliguy said:

Noticed my front passenger side axle is leaking oil. 2016 Sierra with 170k miles. I don’t have any grinding noises and the leaking oil is clear (changed it 20k miles ago). Figured it's probably time to replace the seal. So I called a couple differential/transmission shops near me to quote replacing the seal and one said to first swap the synthetic oil I put in the differentials with conventional and see if that stops the leak. He claims synthetic oil is too thin for axle seals with higher mileage and it seeps through them, plus is doesn't stick to the internals the way it should. Is there any validity to that? What doesn't make sense to me is that I've ran full synthetic in the front/rear diffs and transfer case for over 80k miles now (with one change in there) without any leaking until now. Should I switch to dino oil or go to another shop that will replace the seal?

I don’t believe the mechanic’s claim. I wouldn’t think you would have been able to go over 80,000 miles using synthetic fluid without a seal failing earlier or your dif already failing per his logic. It sounds like to me it’s just the seal failing at 170,000 miles and not because of the synthetic fluid.

Grumpy Bear · January 10, 2023

3 hours ago, midwestdenaliguy said:

Noticed my front passenger side axle is leaking oil. 2016 Sierra with 170k miles. I don’t have any grinding noises and the leaking oil is clear (changed it 20k miles ago). Figured it's probably time to replace the seal. So I called a couple differential/transmission shops near me to quote replacing the seal and one said to first swap the synthetic oil I put in the differentials with conventional and see if that stops the leak. He claims synthetic oil is too thin for axle seals with higher mileage and it seeps through them, plus is doesn't stick to the internals the way it should. Is there any validity to that? What doesn't make sense to me is that I've ran full synthetic in the front/rear diffs and transfer case for over 80k miles now (with one change in there) without any leaking until now. Should I switch to dino oil or go to another shop that will replace the seal?

Not true. Change the seal. They have a life.

midwestdenaliguy · January 10, 2023

19 hours ago, steelerdude15 said:

I don’t believe the mechanic’s claim. I wouldn’t think you would have been able to go over 80,000 miles using synthetic fluid without a seal failing earlier or your dif already failing per his logic. It sounds like to me it’s just the seal failing at 170,000 miles and not because of the synthetic fluid.

17 hours ago, Grumpy Bear said:

Not true. Change the seal. They have a life.

Thanks gentlemen, I share the same thoughts. Even when I pressed him on why the seals didn't leak in the previous 80k miles of synthetic he said it may have finally worn enough to allow it through. Well duh, hence why the seal needs to get replaced. Needed a sanity check here and you guys gave it, thanks. Interesting enough 3 shops have now said they won't do just a seal replacement. They rebuild the entire diff so people don't come back. They have enough business to turn people away apparently. I'd change the seal myself but with a 2 month old, 2.5 year old, working full time during the week, and a wife that works nights and every other weekend...there just isn't time to get these projects done myself.

newdude · January 10, 2023

21 hours ago, midwestdenaliguy said:

Noticed my front passenger side axle is leaking oil. 2016 Sierra with 170k miles. I don’t have any grinding noises and the leaking oil is clear (changed it 20k miles ago). Figured it's probably time to replace the seal. So I called a couple differential/transmission shops near me to quote replacing the seal and one said to first swap the synthetic oil I put in the differentials with conventional and see if that stops the leak. He claims synthetic oil is too thin for axle seals with higher mileage and it seeps through them, plus is doesn't stick to the internals the way it should. Is there any validity to that? What doesn't make sense to me is that I've ran full synthetic in the front/rear diffs and transfer case for over 80k miles now (with one change in there) without any leaking until now. Should I switch to dino oil or go to another shop that will replace the seal?

Synthetics too "thin"? A 75w90 is a 75w90. I see he's still drinking the old timer kool-aid. This all stems from early on synthetics that contained ester that could lead to seal degradation and leakage.

170k if that's the original seal is quite impressive. See them at work leaking way sooner than that.

Time for a new seal! Stick with the synthetics.

As for an entire rebuild, for a seal leak? If the fluid ran low I can understand it.

Edited January 10, 2023 by newdude

elcamino · January 10, 2023

Don’t make the mistake of thinking that mechanics know better, they go by the old petroleum adage of "Thicker is better".

Go walk the Walmart parking lot on a warm summer day and you will have to hop, skip and jump to avoid stepping in leaked oils. Seals are the weakest link. Lube would be very clever to only leak on one side but not the other.

Edited January 10, 2023 by elcamino

steelerdude15 · January 11, 2023

8 hours ago, midwestdenaliguy said:

Thanks gentlemen, I share the same thoughts. Even when I pressed him on why the seals didn't leak in the previous 80k miles of synthetic he said it may have finally worn enough to allow it through. Well duh, hence why the seal needs to get replaced. Needed a sanity check here and you guys gave it, thanks. Interesting enough 3 shops have now said they won't do just a seal replacement. They rebuild the entire diff so people don't come back. They have enough business to turn people away apparently. I'd change the seal myself but with a 2 month old, 2.5 year old, working full time during the week, and a wife that works nights and every other weekend...there just isn't time to get these projects done myself.

Rebuilding the entire diff so people don’t come back… Yeah, sure. More like they’re just trying to make as much money off people as they can.

I hope you can find a mechanic who won’t give you the run around and would change it for you.

midwestdenaliguy · January 11, 2023

13 hours ago, steelerdude15 said:

Rebuilding the entire diff so people don’t come back… Yeah, sure. More like they’re just trying to make as much money off people as they can.

I hope you can find a mechanic who won’t give you the run around and would change it for you.

Yeah it's crazy locally how a lot of these shops say they're 1-3 months out and are giving insane quotes or telling you the repair has to be way overdone. I'll just keep an eye on the oil level and top off as needed until I find someone who's not trying to rip me off. Appreciate all the input.