[2fast4]

2008 335i automatic trans.

Lately I hear thump or bang noise from under the car.
Noise is described as dull "thump" as if hitting carpeted wall with hammer -
- in parking lot low speed decel a bit and hit gas to accelerate, the thump,
- on freeway speeds hit gas go WOT it downshifts from 6 to 3rd or 4th gear, the thump.

I've searched and so far culprit could be guibo disk, center support bearing, low auto trans fluid, trans mount, motor mount.

It does NOT go thump from dead stop which is likely CSB so the confusion.
I want to hear from you guys. Got 185k miles on the clock.

[Saif2018]

Originally Posted by 2fast4

2008 335i automatic trans.

Lately I hear thump or bang noise from under the car.
Noise is described as dull "thump" as if hitting carpeted wall with hammer -
- in parking lot low speed decel a bit and hit gas to accelerate, the thump,
- on freeway speeds hit gas go WOT it downshifts from 6 to 3rd or 4th gear, the thump.

I've searched and so far culprit could be guibo disk, center support bearing, low auto trans fluid, trans mount, motor mount.

It does NOT go thump from dead stop which is likely CSB so the confusion.
I want to hear from you guys. Got 185k miles on the clock.

Have you serviced the gearbox, oil, Seals, sleeves and Solenoids?

[cozzyman]

Originally Posted by 2fast4

2008 335i automatic trans.

Lately I hear thump or bang noise from under the car.
Noise is described as dull "thump" as if hitting carpeted wall with hammer -
- in parking lot low speed decel a bit and hit gas to accelerate, the thump,
- on freeway speeds hit gas go WOT it downshifts from 6 to 3rd or 4th gear, the thump.

I've searched and so far culprit could be guibo disk, center support bearing, low auto trans fluid, trans mount, motor mount.

It does NOT go thump from dead stop which is likely CSB so the confusion.
I want to hear from you guys. Got 185k miles on the clock.

Check the propshaft Rubber guibo.

[2fast4]

Originally Posted by Saif2018

Have you serviced the gearbox, oil, Seals, sleeves and Solenoids?

Only mechatronic sleeve replaced + oils at the intervals.

[2fast4]

Originally Posted by cozzyman

Check the propshaft Rubber guibo.

I will take down the exhaust + shield and check it. It's so hot in Az.

[iqraceworks]

Originally Posted by cozzyman

Check the propshaft Rubber guibo.

....and also the driveshaft u-joint.

[Renner335i]

I had a issue like this. On and off gas i had a loud thump and bang. It was alot more noticable at lower rpms and started to be more violent. Mine ended up being the differential. Pit a used one in and all was good. I could barely turn the diff by hand. I had to use alotttt of force to move it.

[2fast4]

Update: I took down exhaust + shields.
Good news - Guibo disk is in perfect shape. Not even fine cracks.
CSB rubber in great shape. Fine cracks present though. I push upon the shaft and CSB rubber flexes a bit.
Trans mounts also in perfect shape with fine cracks.
U-joints looks good and there is no slop/slack when turning.
I'm surprised these are in great shape.

However rear diff, there are 2, 1 mount 1/2 of the bushing is broken. The other is almost all good, less torn then the other one. Overall, I think they might be OK?
What do you guys think?

Next stop, motor mounts.

[2fast4]

Originally Posted by Renner335i

I had a issue like this. On and off gas i had a loud thump and bang. It was alot more noticable at lower rpms and started to be more violent. Mine ended up being the differential. Pit a used one in and all was good. I could barely turn the diff by hand. I had to use alotttt of force to move it.

I think you hit the nail on the head...my diff 3 mounts(2 lower front + 1 rear top) are broken though not severely.
If I try to turn the driveshaft it turns smoothly.
I have not yet got to the engine mounts...hot Az weather.

How hard is it to replacing the 3 diff mounts?