Guess the cause of my e46 diff/drive shaft knocking sound!

[mlmcelligott]

Howdy, I'm brand new here so hi everyone

My e46 320d has developed a knocking noise from the rear diff area. Initially my mechanic thought it was the doughnut / universal joint / guibo (No.2) and the center mount support bearing (No. 7) so they were changed. It’s improved a bit (cant feel the knock off the drive shaft tunnel now) but theres still a slight knocking sound when pulling away in first or accelerating out of a turn in second. From 3rd up it drives fine. My indy told me he couldn’t see anything else without removing lots of covers or the diff to inspect the rest.

Could it be the rear center mount bearing (No.14) or diff mounts or something else?

[Valdelisbmw]

diff back mount or damaged boot floor

[JohnH]

Hi,
Welcome along. As Valdas suggests it could well be the floor. My first e46 had the torn boot floor / subframe issue and it sounded like that.
It's not the end of the world to fix and @[Valdelisbmw] has done plenty of the at this stage.

[Valdelisbmw]

Hi,
Welcome along. As Valdas suggests it could well be the floor. My first e46 had the torn boot floor / subframe issue and it sounded like that.
It's not the end of the world to fix and @[Valdelisbmw] has done plenty of the at this stage.

John ,don't scare him :hehe!: it could be just diff back mount :happy:

[JohnH]

Hi,
Welcome along. As Valdas suggests it could well be the floor. My first e46 had the torn boot floor / subframe issue and it sounded like that.
It's not the end of the world to fix and @[Valdelisbmw] has done plenty of the at this stage.

John ,don't scare him :hehe!: it could be just diff back mount :happy:

Ha! Fingers crossed

[Ford 2]

Could be an output shaft either, was that checked ? Mine was gone ever so slightly, slight play and would tick ( knock ) under acceleration at times and go away other times also

[mlmcelligott]

Could be an output shaft either, was that checked ? Mine was gone ever so slightly, slight play and would tick ( knock ) under acceleration at times and go away other times also

how do you check it? I had the boot full on the way home and noticed the problem was more apparent with a bit of weight in the back

[Ford 2]

Well the output shaft is the drive shaft going to each wheel left and right..jack car up and hold the inner drive cup at the diff, then move the wheel while holding the cup tight and feel/listen for any play, try both sides, any metallic noise will be a wore cv possibly, can't really change cv so in my case I put a full drive in it, there unequal lenght

[John_D]

My money is on the diff bushing, very common problem.

[mlmcelligott]

Thanks Guys, while looking for videos on youtube to learn about the read diff bush I found this video about worn diff mounts. The thud sound you can hear in the video sounds very similar to the shudder I hear and feel as I pull away. Gonna have my mechanic have a look at them

https://www.youtube.com/watch?v=GzLZkJPJsbs