Just bought my first BMW - Is there a DIY for replacing the rear differential?

[humsaffering]

I'm in love with the car I bought, It is a 2006 e90 330i with a 6mt.

I bought it for $6500 with 112k miles but it comes with a few issues that I need to fix. I like the color and interior a lot, so I decided to take the risk. There is a hum coming from the back whenever the car is running, almost like an exahust note.The seller told me that he took it to a BMW mechanic, and he was told that he needs to get his differential swapped with a new one, he was quoted $1000 for the job.

I was just going to find a diff from a car that was parting out, is it a tough job to do on my own? There are no DIY's online, I am not sure how I would even approach changing the diff. Would this have to be done at a mechanic? Looking online, my diff ratio is 3.15, would there be any complications if I replace it with a diff from an automatic E90 (which I believe has a higher ratio?).

He also told me the valve cover gasket is leaking, it was burning a quart of oil every six months or so. I figured that this was a common problem and only requires a gasket replaced, but online quotes around my area are running around $700. Is this something I can approach on my own?

I don't think there are any other issues with the car, I'm glad I only spent $6500 instead of buying a 2018 WRX for $26k. I am just worried about the maintenance and I am not sure what I bought into, I just bought it and it looks like I'm already going to be putting in $2k to get it fixed.

[bmwdirtracer]

Welcome to the forum.
I'd first have to caution you to get a second opinion.

The wheel bearings are a whole lot more common cause of a hum, than the diff.

But you said : " a hum coming from the back whenever the car is running, almost like an exhaust note". If you were accurate in this statement, you absolutely do NOT need a diff, OR a wheelbearing.

A diff or wheelbearing can only possibly make noise when the car is MOVING. A diff noise will change, when you go on and off the throttle. A wheelbearing noise will change when you corner to one side, as opposed to the other.

Either noise needs to be confirmed, using a stethoscope, with the car in the air, ABS unplugged, or, at the very least, the DST button held down for 5 seconds. (Whatever you do, it will set codes which must be erased, but you must absolutely do one of these, before you spend a bunch of money fixing something that's not broken.

I don't know you, nor do I know your abilities and what tools you have available, and I mean no offense, at all.
But I would not consider either of these to be a job that should be attempted by someone with "entry-level" tools or experience.

IF your noise is truly present when the car is not moving, but engine running, try seeing whether there's a difference, between being in park, or reverse. or drive.

If the noise is present when the vehicle isn't moving, your diff and wheelbearings are not at fault.

[shadowpuck]

some suggestions:
1) join BMW CCA and ask your local chapter for recommendations on good local shops. take the car there for an inspection (which is best done prior to purchase) and have them diagnose this issue.
2) if you are going to do things DIY - pick up a bentley service manual and also become good friends with good local shops.....
3) maintenance, maintenance, maintenance....

[humsaffering]

Welcome to the forum.
I'd first have to caution you to get a second opinion.

The wheel bearings are a whole lot more common cause of a hum, than the diff.

But you said : " a hum coming from the back whenever the car is running, almost like an exhaust note". If you were accurate in this statement, you absolutely do NOT need a diff, OR a wheelbearing.

A diff or wheelbearing can only possibly make noise when the car is MOVING. A diff noise will change, when you go on and off the throttle. A wheelbearing noise will change when you corner to one side, as opposed to the other.

Either noise needs to be confirmed, using a stethoscope, with the car in the air, ABS unplugged, or, at the very least, the DST button held down for 5 seconds. (Whatever you do, it will set codes which must be erased, but you must absolutely do one of these, before you spend a bunch of money fixing something that's not broken.

I don't know you, nor do I know your abilities and what tools you have available, and I mean no offense, at all.
But I would not consider either of these to be a job that should be attempted by someone with "entry-level" tools or experience.

IF your noise is truly present when the car is not moving, but engine running, try seeing whether there's a difference, between being in park, or reverse. or drive.

If the noise is present when the vehicle isn't moving, your diff and wheelbearings are not at fault.

The noise is only present when I am driving, but it gets louder as the revs go higher. Sorry if that was not clear. I believe it was a certified BMW mechanic who said this, but he wanted $1000. As for the valve cover gasket, I have done spark plugs, ignition coils, brake pads, on my civic and prius but I am not crazy mechanically inclined.

I want to approach it step by step, but just worried. How soon would I ahve to replace both of these before it affects something else?

[bmwdirtracer]

Valve cover gasket job on this car pays 4.9 hours to a pro with all the tools; it is not an easy job, and a first-timer will likely break the hose on the back.

Differential noises usually consist of whining, more under either acceleration or deceleration. Has anyone checked the fluid level? Does the noise change when you corner to either side? I'd still have to recommend that you get a second opinion, from a BMW pro who YOU asked to diagnose it. I would not trust the second-hand information.

There's no way to know how long you have before something bad happens until you get this inspection.

[MarcoZandrini]

The Golden Gate Chapter of the BMWCCA is a very active chapter. Check its website for shop recommendations. Definitely check the differential for fluid but I’m betting the exhaust system is the culprit.