Pinion seal replacement + diff fluid question

[TexaZ3]

About to replace pinion seal on my diff, and having not done it before - do I need to drain the fluid in order to change it? I just did the fluid change like, 1000 miles ago, so would hate to discard perfectly good fluid.

If I do - is the Castrol 75W-140 SAF-XJ + FM still the way to go? Or is there something better out there (aside from super overpriced OE fluid)? Thanks!

[COVID-19]

Don’t know if you need to drain any but I started doing this for diff oil.

https://youtu.be/lUpOFxGtN-E

[Slideways]

If you are trying to save and reuse the diff fluid, one way would be to thoroughly clean the drain bolt area and drain the fluid into a clean container (an empty OE diff fluid bottle or maybe a 10W60 container rinsed with brake cleaner). I was trying to think of a clean method of saving the diff fluid as well if replacing the diff cover.

[TexaZ3]

I'm not really trying to save diff fluid, I'm trying to save my time and money. If the fluid will leak out when changing pinion seal, then I'll just replace it - I just don't want to spend the money and buy it, if I don't really need it. All the videos I see don't show anything leaking out, but then again, I don't know if the diff is already drained at that point.

[bigjae46]

You may need to top off the fluid afterwards but a majority of the oil sits in the bottom of the case. The pinion bearings do not sit in oil. The pinion is lubricated when the ring gear spins and forces fluid over the limited slip carrier. If you look at the inside of a diff cover, it is curved to aid in the flow over the carrier.

[TexaZ3]

You may need to top off the fluid afterwards but a majority of the oil sits in the bottom of the case. The pinion bearings do not sit in oil. The pinion is lubricated when the ring gear spins and forces fluid over the limited slip carrier. If you look at the inside of a diff cover, it is curved to aid in the flow over the carrier.

Terrific - thank you!

[sapote]

About to replace pinion seal on my diff, and having not done it before - do I need to drain the fluid in order to change it?

Look careful to see if the pinion shaft is located higher or lower than the diff oil filling hole. I think it is higher or about the same.

[M3GA]

No need to drain fluid, though check level when done. If removing the diff to replace pinion seal, know that there's a weep/breather hole in the back cover. So if u stand up the diff (pinion facing up) fluid will leak out.

Ask me how I know 🙄

Sent from my SM-G960U using Tapatalk

[TexaZ3]

No need to drain fluid, though check level when done. If removing the diff to replace pinion seal, know that there's a weep/breather hole in the back cover. So if u stand up the diff (pinion facing up) fluid will leak out.

Ask me how I know 🙄

Sent from my SM-G960U using Tapatalk

Thanks, no - not taking diff off. Will make sure to top off!

[Slideways]

No need to drain fluid, though check level when done. If removing the diff to replace pinion seal, know that there's a weep/breather hole in the back cover. So if u stand up the diff (pinion facing up) fluid will leak out.

Ask me how I know 🙄

Sent from my SM-G960U using Tapatalk

Is it possible to replace the diff cover while leaving the fluid in the unit? Any chance of fluid leaking out of somewhat older front or side seals?

[M3GA]

Is it possible to replace the diff cover while leaving the fluid in the unit? Any chance of fluid leaking out of somewhat older front or side seals?

Need to drain fluid if messing with the diff cover.

Last year I removed the diff, pain in the a$$ job and replaced pinion and axle seals and front bushing. Then a few weeks later pressed out the bushings in the diff cover, 2 rear and top cover bolts were a pain while diff in car but doable. Used new paper seal, but u can use gasket maker.

Sent from my SM-G960U using Tapatalk

[Slideways]

Need to drain fluid if messing with the diff cover.

Last year I removed the diff, pain in the a$$ job and replaced pinion and axle seals and front bushing. Then a few weeks later pressed out the bushings in the diff cover, top bolts were a pain while diff in car but doable. Used new paper seal, but u can use gasket maker.

Sent from my SM-G960U using Tapatalk

Forgot to mention that the diff would be out of the car and tipped towards the front seal.

[M3GA]

Forgot to mention that the diff would be out of the car and tipped towards the front seal.

Yeah u could do that or stand it up safely, cover upwards.

Sent from my SM-G960U using Tapatalk

[mtpktz]

Does everybody recommend Castrol + FM? Or something like LiquiMoly + FM?

[TexaZ3]

Does everybody recommend Castrol + FM? Or something like LiquiMoly + FM?

I think BMW fluid is Castrol SAF-XJ + FM, so safe to say that's probably is the way to go. Amazon has SAF-XJ on sale right now for $25 per liter.