Oil dripping from the rear...

[starship1701a]

i just noticed oil on the parking stall floor, looks like from the rear end area, it's clear and thick... haven't had a chance to get under the car yet...

Does anybody know about leaky rear ends? common? uncommom? easy fix? difficult?

Furthermore, not knowing how long it's been leaking, how bad can it get if i lose too much oil?

[TxGR8White]

• Rear diff cover gasket can cause leaks
• common on older cars (any car)
• easy fix - get a new gasket
• if you lose too much oil, it can get expensive - seized gears

[starship1701a]

thanks Steffen... so no chance it's anything else right? at first it looked like gasoline...

[TxGR8White]

thanks Steffen... so no chance it's anything else right? at first it looked like gasoline...

well, since my cyrstal ball is out being repaired, I can't tell you with 100% certainty that this is what it is. My response was based on your description. If it was gas, you would have smelled it and it most likely wouldn't be "thick" as you pointed out.
I would check the input shaft to the differential and see if your leak orginates there. It might also be leaking in both areas.
My advice is generally to thouroughly clean (degreaser and power wash) the unit , and then you will be able to see exactly where the oil is coming from.
Do not ignore or put this off - you haven't lived unti you try to replace a differential....

[IcemanBHE]

You have not lived until you froze a diff driving down the highway.

Can you say 3 loops and in the ditch? I can.

(Make sure you fix the lube leak.)

[llcarlos]

• Rear diff cover gasket can cause leaks
• common on older cars (any car)
• easy fix - get a new gasket
• if you lose too much oil, it can get expensive - seized gears

I took my M73 in and the dealer says the rear subframe has to come down to change the cover gasket on the diff. They checked the service menu and the fix is listed as a 5.5 hour job. It's a pretty good leak and left a one foot diameter spill. So on this visit they just made sure the diff was full and sent me home until next week. I don't want my exhaust sawed off. I saw the leak and the cover. Not much room but it would be a design flaw to not be able to remove the cover and replace the gasket easily. Is an M73 different? They've only seen my car and have limited experience.

[testify]

I'm surprised the said the subframe had to come out. The diff pops right out of the subframe with 3 bolts once the axles are disconnected, and there is nothing on the subframe in the way of dropping it.

[llcarlos]

They also have to do an alignment after the job is done. It leaks too much to leave it. Car seemed better with fresh fluid too.

[llcarlos]

I'm surprised the said the subframe had to come out. The diff pops right out of the subframe with 3 bolts once the axles are disconnected, and there is nothing on the subframe in the way of dropping it.

Yes they said the diff has to come out OR the subframe has to be dropped. I can't remember exactly what I saw but yes why wouldn't the diff drop straight down or why wouldn't the diff cover just drop straight down If there are gears behind it
maybe it can't clear the bar that runs across the diff? Did they not want to try to take it off because then it would really be leaking if they couldn't finish the job. Does BMW not show the procedure in their manuals? So confused. I told them you guys said it was easy.

[testify]

The diff cover has two bolts that go through it that attach the diff to the subframe. The cover is actually a structural part of the differential. The diff has to come out before you remove the cover.

Book time is book time, but anyone with a lift and basic hand tools can get the diff out of the car and opened up in 20 minutes.

Figure 45 minutes or an hour if you're working on your back with jack stands.

[llcarlos]

Thanks testify. That makes more sense. No sawing off the exhaust. No alignment. Just undo the bolts and lower the diff. It's a modern BMW dealership. They have all the tools. Why would they not know to just drop the diff?

[dragon850]

Differential does not have to come out just needs to be lowered to the point of the rear cover clearing the sub frame bar. Tell them to take a hike and go find another shop.
However on M73 you do have to cut off the exhaust to lower the diff, for some reason BMW did not put the exhaust section on flanges, good time to ditch the center resonator and go with an X pipe!

[XAlt]

What about the output seals?

[llcarlos]

Differential does not have to come out just needs to be lowered to the point of the rear cover clearing the sub frame bar. Tell them to take a hike and go find another shop.
However on M73 you do have to cut off the exhaust to lower the diff, for some reason BMW did not put the exhaust section on flanges, good time to ditch the center resonator and go with an X pipe!

So should they just lower the diff and leave the subframe alone? It stinks that they have to cut the exhaust. And it should take all of 20-40 minutes except for cleaning up the mating surface and replacing the gasket work and repairing the exhaust?

[8eights]

Take it to a indy muffler shop and have flanges installed on the rear of the exhaust for easier access to other repairs, Like the older cars, then lower the subframe as mentioned, Clean old gasket off, Put a thin lair of Reinzosil on the diff and cover and reassemble with new gasket, it will never leak in this section of the diff again.

[llcarlos]

Ok I'm panicking for nothing. First they don't have to cut the exhaust they just have to remove it. Second, it doesn't really matter how they do it as long as they put it back together and it doesn't leak anymore. They won't charge me 5 hours, that's just the book rate. I don't trust any other shop in my city. The indy is cheap because he doesn't offer the same service as BMW. I ask him a few years ago and he said he would never work on an E31 again. Too many badly neglected 8s here. I think he said one had such bad coolant he was dumbfounded. Now the question is whether to lower the diff or lower the subframe. I'll let them figure it out but it would make sense that the diff is attached to the subframe so the diff should be lowered.

[kiwiCSi]

Have we eliminated the input (pinion) seal?
That was leaking on my CSi when I first bought it - seal replaced and no more leaks.

[llcarlos]

Yes it has been eliminated. Car was up on the BMW hoist and we looked it over. I knew there was a problem when the tech went twice to talk to the service advisor. Then they filled it up and sent me home because of time and the holiday. It's an M73 so a bit different than the others I guess.

And how did the pinion seal get replaced? I would like to know the steps and how long it took. Should be almost the same for the diff seal.

[kiwiCSi]

Dealer did it during Inspection II service - I merely supplied a new (BMW) seal, and didn't actually observe the job being done.
Wondering what the outcome was for the OP of this thread?

[8eights]

2 hour job.

[llcarlos]

I'm surprised the said the subframe had to come out. The diff pops right out of the subframe with 3 bolts once the axles are disconnected, and there is nothing on the subframe in the way of dropping it.

I think they want to lower the sun-frame a bit to get at some of the bolts. They have to remove the exhaust. They are not removing the wheels, springs, or shocks but the car will need an alignment after this job. They said this is quicker than removing the half-shafts and the other drive-line parts, propeller shafts? I have no idea. I trust the dealer and I have no other shop choice. It's too far to BC.