S430man

05 S430 4matic 158k miles. I've had it for 1 year and 3k miles. 2nd owner had the car from 30k miles to 155k and it appears to have been maintained at a dealership. However, the maintenance is unknown.

Discovered a noise in the driveline that needs identified. It is consistent with the shift into and through 3rd gear comfort mode around 28mph. It sounds like the Jetsons (a high pitched, consistent, fast wha wha wha wha) with a noticeable whine as the shift goes into 3rd and remains with 3rd gear. The sound is speed sensitive and loudest with acceleration/load. The sound comes from the passengers floor near the wheel well. It is most noticeable when cold and improves when warmed up. It seems like it is more noticeable with time. I think it is only 3rd gear, but I will confirm when I next get on the highway.

I just replaced the Lower Control Arm on the passenger side along with both sway bar links, passenger air shock, and front pads/rotors. The passenger drive shaft felt good and the boots were good. Bearings were good and tight. Everything is tight and the suspension is squeak free now! This makes the noise more noticeable and it's on my mind...

What are some things to try to isolate the noise?

- I'm guessing it is transfer case or trans related. Next time I'm out I will try to get a video of it.

S430man

Here is a video with the noise. It is hard to hear but if you listen for a high pitch repeating noise that is tied to the RPMs of the 28mph shift point, it is there.

https://youtu.be/odbZz4ibKug

S430man

Ok, so the noise remains constant with the engine speed in that one gear only regardless of turning or breaking. I did the manual shift and the noise is actually in gear 4 and only in gear 4.

The noise has been quieter now that I'm driving around trying to get a good recording of it. I have a new theory that this may be related to the car sitting a lot (<3k miles last year) and maybe with some regular driving it is getting the fluid moved around and the noise is going way?

S430man

Did trans fluid and filter change with Pentatosin 134 fluid with genuine mb filter/gasket. The old fluid was no longer red, but still clear and smelled normal.
The pan had no metal but a good layer of black gunk. Cleaned the pan and magnet. The sound improved for a few miles then slowly returned. Not as noticable as before, but still there.
Maybe this is heading in the right direction? Maybe because I only dropped the pan and didn't flush the torque converter when the old fluid mixed with the new fluid the sound returned?
I bought 10L of fluid and still have 6 after first exchange. Maybe I should drain and fill again?

S430man

Just a little gunk on it, very happy there is no metal flakes!

Unfortunately also found this... Got to clean it up and see how bad it is. Reading around, this is expected for this age and miles. Gonna try some molly lube to rejuvinate seals. Seen others here had success. Figure it can't hurt.

gakali

Generally speaking, a whine from a transmission while in a specific gear signals a hard part issue such as a bearing or gear set. Something that is "activated" while in that particular gear. Under load would more likely be a gear set issue. Maybe research the power flow through the transmission while if fourth gear to narrow it down if you really need to know, as some minor gear set noises aren't necessarily a reliability concern.

Sadly, my rear main is a bit juicier than yours and I see a tranny re-and-re in my future. At least being a rear wheel drive simplifies my job...

S430man

Thanks for the info. It is helpful to know it is not a reliability issue. Thankfully it is not noticable when the stereo is on.

Hope you fare well on your repair.