325ix Vibration coming from car at higher speeds

[SMJ325ix]

I just had the rear diff replaced. I took my car to the local BMW shop to have a "thump, thump" feeling checked into.
The techs at the shop I take it to had explained the rear diff was shot and the bearings went bad and that was what was making the faint "thump, thump" feeling and the vibration at around 70 mph.
However, that thumping is still there at very low idle through, say a parking lot.(as it was before) Not as noticeable at times but its definitely there.

Tonight however, I wanted to see if the vibration was completely gone at around 70 mph??.... I took her up to 85-90 and the vibration was really bad!
Especially when you let off the gas then it was vibrating pretty strong, felt like it was coming from the rear. So that's got me both puzzled, and pissed as this was supposedly all taken care of!
Not to mention, the bearings in the transfer case are shot (whining when on a lift).... so they'll have to be replaced.


Any ideas here guys?
The car only has 81,000 miles on it, so I 'm thinking the fellow I bought it from initially let something go for the rear to have gone bad?? (Hence the replacement of the rear diff)

Thanks in advance.

[flyboyx]

sometimes low mile cars have more problems from just sitting that a high mile car that was well maintained.

there really isn't enough info provided to give you a definitive answer. however, the rear guibo might be a place to look. check your axle boots to see if they are ripped or have been that way for a really long time. you might have a bad axle. driveshaft could be out of balance. just to name a couple things.

[SMJ325ix]

sometimes low mile cars have more problems from just sitting that a high mile car that was well maintained.

there really isn't enough info provided to give you a definitive answer. however, the rear guibo might be a place to look. check your axle boots to see if they are ripped or have been that way for a really long time. you might have a bad axle. driveshaft could be out of balance. just to name a couple things.

Actually the low mileage car here was both well maintained and driven weekly (albeit not for any long distances) by the "original" owner. The guy I bought it from, who knows what he did or didn't do??
But I have a ton of receipts for the car, but all of those are from the original owner, not one from the cars second owner, (as I'm now the third owner).
Boots on axles are fine, I checked those right off the bat. Though I still wonder about the axles regardless.
Driveshaft being out of balance or bad axle being just slightly out really makes sense for what I'm feeling,...I'm going to have to mull over a few things to get to the bottom of this.

Thanks for the info and suggestions,.. much appreciated. Have a great Christmas!

[gw ix]

Also check wheel bearings and tires.

And check the air pressure in your tires. I know this sounds stupid, but 9 out of 10 that I check are off.

[SMJ325ix]

Also check wheel bearings and tires.

And check the air pressure in your tires. I know this sounds stupid, but 9 out of 10 that I check are off.

Thanks.
Could the wheel bearings really cause that kind of vibration, or that much?
Actually topped off the air in the tires a few days ago....and wheels look fine all over as well. They were put on in August of 2011, and not many miles were put on by the previous owner. I was looking for flat spots and could not find any...

[flyboyx]

anything is possible but normally, a wheel bearing will just cause a loud noise that you can make go away for a moment by sideloading the car such as taking a turn.

not that this is your problem, but i once had a bad vibration with my ix. it turned out that 3 of the 4 tires had a few ounces of water in them.

[z122643]

So...

I just replaced my rear wheel bearings. (to add to the flavor the ball bearings in the bearings were rusted, just to get the idea of how bad my bearings were)
Wheel bearing noise/vibration is usually most noticeable at low speeds (10-30). I doubt you have a bearing problem.

TO CHECK: have the car lifted (on a mechanics lift not jack stand stilts) have someone in the car and engage first gear (or drive if automatic). You just have to get the tires moving (5mph). Place your hand (yes your hand) on the bottom of the rear shock mount of each side. Feel for vibration, it will be obvious. If you can't tell, it isn't the problem!

You say the rear diff has been worked on? Replaced? Was the thumping there before replacement or after?

Because your symptoms are classic driveshaft imbalance. This could have happened when the driveshaft was removed in order to replace the diff. The rear driveshaft is actually two parts, so as to be adjustable. If the rear portion of the driveshaft was slide out (accidentally) and slide back in a different position, that is enough to create an imbalance. Symptoms would be vibrations from low speeds increasing in severity at higher speeds. Especially when not under load (taking your foot off the gas).

*as a side note, it is also completely possible that your mechanic (by accident) forgot to tighten the 4 bolts that are on top of the diff which secure it to the chassis. These bolt are not easy to get to and can be easily overlooked.

Please tell us what you find out.

[vert_this]

"search" the problem tons of IX's with similar issues. I had one that I nor an independent could resolve. Some say CV's some say SUBframe mounts, diff., wheel bearing, rotors, driveshaft, tranny mounts u name it. So research it or it will cost you tons. I gave up and went back to 2WD's.