[BimmerG0d]

Hi guys,

Lately I’ve noticed when I’m on the highway going 60+ and let off the throttle/Accelerator and the car is slowly slowing down I hear a hum from about 50mph going down 40mph from the rear of the car, if I accelerate the sound goes away. What do you guys think I should look at?

I have a 2007 328xi with 149k miles.

Thanks

[Dunt1]

Diff? Have you ever changed the oil?

[Volasko]

Without some sort of video its hard to tell, but wining when you get off the throttle does sound like a differential issue. You have a x-drive so it could be either front or rear.

[gbalthrop]

Originally Posted by BimmerG0d

...Lately I’ve noticed when I’m on the highway going 60+ and let off the throttle/Accelerator and the car is slowly slowing down I hear a hum from about 50mph going down 40mph from the rear of the car, if I accelerate the sound goes away...I have a 2007 328xi with 149k miles.

Whine on deceleration, but NOT when holding steady speed on level, or accelerating, is usually from too-loose contact between the pinion gear (driven by Driveshaft) and the Ring Gear. I have NOT had any occasion to get into the BMW Differentials, but the same probably applies, even though TIS calls those components by different names. Here is TIS page dealing with replacement of what is commonly called the "Pinion Shaft Seal". Note the first two photos, and the "Flange Nut" and "Bevel Pinion":
https://www.newtis.info/tisv2/a/en/e...th-lid/4LWolh0

With older differentials with which I am familiar, there was simply a "Pinion Nut" which was torqued to a specified figure upon assembly which properly established gear mesh between the pinion gear and ring gear by compression of a "Crush Sleeve". This differential would appear to have a similar internal setup, due to the fact that the second photo shows "Mark Installation Position of Flange Nut to Bevel Pinion". Upon reassembly after changing the seal, one would restore the Flange Nut to exactly the same position. If too loose, whine would occur on deceleration. If too tight, further compression of "Crush Sleeve" would occur, AND wear of gears (or worse) would occur.

The E9x setup is more complicated, requiring special tools. On a Jag XJ-6 built 30 years ago, I had sudden onset of decelaration whine from differential and immediately took vehicle to Jag specialist who properly reset pinion nut (which HAD loosened), all in ~ 1 hour while I waited, and NEVER had any issues, whine, etc. for ~ 15 years of ownership thereafter.

I have no idea whether BMW Indy's or Dealers have torque spec for re-torquing loose "Flange Nut" as the Jag Indy had years ago, but they SHOULD if the setup is as I described.

ANYONE who has done this or had it done who can confirm/correct?

George

[ramp]

Interesting info. My e91, 6 speed manual is experiencing this same issue. Get on it and is fine. Drive around slow and pronounced noise on deceleration.
Just had all the fluids changed 3 months ago.

[ramp]

Dropped off at shop to diagnose where noise is coming from.

[e90yyc]

gbalthrop

My original front diff is whining... definitely pinion related. I’ve got a replacement on the bench and am putting new seals in. The pinion seal instructions (TIS) are very clear that you must not replace the nut, and must return it to the exact position it was from the factory. I’ve watched a YouTube video of a guy rebuilding one of these diffs, and for the torquing down of the new pinion nut, his method relied on “feel,” in that you’d tighten down a bit, check for play, tighten more, and so on. I’m not overly fond of those ambiguous methods, but this guy clearly had experience and knew how to do this. Me? Not so much.

If my whining (and OP’s) can simply be fixed by tightening the pinion nut a bit more, that would be great. The weather where I live is absolute dogshit right now, so unfortunately I can’t try this out for a bit. When it warms up, I would be open to trying to tighten the nut down a bit more and see if that helps. I guess if the diff grenades, at least I have a replacement waiting.