Author Topic: Whaling buzzing sound from dash when cold.  (Read 79 times)

OLDGOLD

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  • W116 Enthusiast
  • Location: Dallas, TX
Whaling buzzing sound from dash when cold.
« on: 05 March 2019, 06:01 AM »
Hello! When it's below 25 degrees Fahrenheit, like it's been in Dallas the last couple days, and I start driving the vehicle a few miles after cold start I will get a sudden, very loud buzzing noise from the dash. The noise seems to go away once I let off the accelerator pedal and the vehicle slows down. It's super loud and sounds similar to the light switch buzzer, but more of a whaling noise combined with it. This happens after letting the vehicle warm up at idle for 15 minutes. I've also noticed that the brakes become more stiff and the engine takes a hair longer to shut off. I'm nearly certain that this has to be vacuum related, but why does this only happen on the coldest days of the year below 25 degrees? I've checked the vacuum lines near the fuse box under the hood, but I must be losing vacuum elsewhere. The sound seems to be coming from inside the dash on the right side of the instrument cluster.

I've also noticed that the heat won't work even with the engine at operating temperature, unless I cycle the ACC temp wheel to full cold, then back to heat, then it usually works. I know that these are supposed to be great winter vehicles, since they are German after all, but is this normal? I couldn't imagine living somewhere cold like Alaska, Finland, Canada etc. and having these sort of issues.

Any help would be appreciated!

Diesel 617

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  • 1980 300SD 0M617.950
  • Location: Illinois
Re: Whaling buzzing sound from dash when cold.
« Reply #1 on: 05 March 2019, 06:56 AM »
Sounds like the dash sound occurs while driving. Pull your instrument cluster and remove the speedocable and pour a about half a cap full of trans fluid down the cable. No more ear piercing horror sounds from the dash :)

Leaky vacuum, hoses shrink from the cold and the seal quality is wearing out at 40years of age.

You have automatic ACC? Could be a sign the servo internals are starting to leak causing corrosion, or the amp if it is original is starting to go faulty. Test the resistance on the motor would help you answer this question.
https://forum.w116.org/mechanicals/1980-300sd-climate-control-monovalve-manipulations/msg131665/#msg131665
1980 300SD
2 OM617.950 complete with transmissions
1980 450SEL Transmission (for sale 150kmi 100$ + freight)

In my imaginary garage
European 1974-76 450SEL 6.9 Green Velour

OLDGOLD

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  • W116 Enthusiast
  • Location: Dallas, TX
Re: Whaling buzzing sound from dash when cold.
« Reply #2 on: 05 March 2019, 09:07 PM »
The servo and amp were replaced with the electronic upgrade kit.

I was asking a technician today and he though it could be from a tear in a rubber diaphragm under the dash that shrinks in the cold possibly. I’ll try the trans fluid.