[Polaris8030]

At the last oil change, shop notes said "rear differential leaking badly". I asked the mechanic how bad is bad and he said that it should be the next thing on the fix list, price tag : $900. I asked if the fluid could be all removed and then new fluid added back in .. Apparently that's not an option at the shop.
Then later, I pulled up the notes from the oil change at 45K .. Different shop ... Also notes differential leak
A look under the car shows grease on the differential, ostensibly, from the deteriorating seal. I, don't see any leaks around either axle.

Given that leak precedes 2 oil changes and I've done 25K miles without noticing (not sure how to test either ) .. How urgent is this fix based on, what you see .. In other words, next week or next year, and 2 nd question .. Can a flush and fill work for the time being ?

Photos
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Thanks
B P

[Nitrousbird]

Your pics are all X's.

I sure hope you wouldn't pay $900 to fix a diff leak. Why would you need to flush and fill for a diff leak? If it isn't bad, top off and be done. If you have enough miles, just drain, refill and top off as needed.

If it is bad, drain, fix, refill, done.

[kkasson]

Also can't see the pictures, but on the E90 the diff cover is fairly difficult to remove. You can't just remove the cover because one of the diff mounts is in the way. I'm not sure if you need to fully remove the differential from the vehicle or if you can just remove the mount, but even removing the mount is a fairly big job I believe.

Assuming the cover is where it's leaking, the fluid will be drained when the cover is removed. The differential doesn't have a drain plug, only a fill plug. So you can't exactly do a drain and fill...if you want to remove the fluid and replace it, you have to use a pump to pump the old fluid out of the fill plug and then refill it with new fluid. But if the cover comes off, all the fluid will drain out anyway.

I would just refill it in the mean time and see how low it is. With the vehicle level, you just remove the fill plug and oil should drip out of it. If there's no oil dripping, you pump oil in until it begins to slowly flow out of the fill hole, then it's full.

It uses a special fluid, I wouldn't recommend using standard gear oil. Others have done so and it hasn't caused any immediate harm, but it originally came with a special fill. It's Castrol SAF-XO fluid, you can get it at the dealership but it's expensive. Something like $50 a liter. I found that it was a lot cheaper at the BMW motorcycle dealership. I paid $21 for the liter, which is only slightly more expensive than normal gear oil. It's sold as Final Drive Oil for the motorcycles, but it should say SAF-XO on the label. It's the same fluid.

I would be sure to take it to a shop that specializes in BMWs for whatever repair you do. I'd also buy the oil myself and bring it to them.

[Polaris8030]

Photos fixed, Sorry .. A little new to posting on forums through a phone ... The copy paste was broken.
Thanks for the responses .. I like the idea of pumping out the old and pumping in the new for the diff fluid ... Something I can totally do ..
Kkasson .. Thanks for the tip about the oil from the motorcycle dealership. One question .. How many litres am I looking at replacing ?

Thanks
Brian

[bdhh]

If you can get all the old oil out it takes slightly more than 1 litre so buy two

[Manberg]

Thats not that bad at all, its not leaking to a drip. Have you had to add any oil to it? If not or just a small amount I would worry about it. Id have it checked at every oil service like its sounds you have been doing.

[kkasson]

On the forums I've always seem it said to be 1 liter, but the book is saying the full filling capacity is 1.2 liters.


But yeah, doesn't look very bad so I'd definitely just refill it for now and see what happens. The motorcycle dealership sells the oil in 1 liter bottles and either 200 or 250ml bottles, so that will get you exactly what you need if you end up needing to refill it completely.

You might start with getting the small bottle and just topping it off with that.

[Ozzie335i]

If you end up needing to put in new gaskets and seals you might consider an MFactory LSD. Not much more than 900 if bought during a sale.

[Manberg]

I replaced my diff with a MFactory LSD because of a leak that led to failure. Mine was actually leaving oil marks on the ground though.

[Hacksaw]

Not a bad leak but considering how much one of these diffs holds.. I would check the oil level at least.

Mfactory LSD is the way to go..why a proper LSD was never placed in this car is beyond me. All the ingredients of go fast and then you get to the diff and it leaves you with that sad feeling. With an M3 in the livery I will be making this diff disappear soon enough. For A to B... sure it does its job. But for a "drivers car" it doesn't fit honestly.

[muncie21]

If you don't have extra money to burn, I'd wait until I saw drips on the driveway. That's ghetto I know, but a man's gotta have priorities

[Underground6t9]

I don't understand if you know you have a leak why not fix it. People always wait till the last minute when something breaks. Know if you cant afford the fix go buy a different car that requires less maintenance. Live within your means.

[BravoJohny33]

Originally Posted by Underground6t9

I don't understand if you know you have a leak why not fix it. People always wait till the last minute when something breaks. Know if you cant afford the fix go buy a different car that requires less maintenance. Live within your means.

Because sometimes you can just fill something and be good for a year. Much cheaper to just fill the diff every year than replace. My car has had an oil pan leak for over a year now and its not been a problem at all. The shops around here want 1100 + to fix the leak.

[mrw84]

Originally Posted by Underground6t9

I don't understand if you know you have a leak why not fix it. People always wait till the last minute when something breaks. Know if you cant afford the fix go buy a different car that requires less maintenance. Live within your means.

This, or learn to fix it yourself.