Raspy noise from transmission

[yellowbenz]

I'm hoping someone can help me identify this noise and its implications.

The car is 1978 300D with 157000 miles. No vacuum control on this transmission.

The noise is coming from under the car seemingly from the transmission. It is a distinct metallic rasping/rubbing sound at idle or when decelerating. With acceleration or at speed it doesn't make the noise. Let off the accerator and there it is (the noise). I've got a firm first shift. The others are smooth. Readily downshifts and will hold shifts if accelerating. Fluid is pink/red and proper level at temperature.

I'll have to take it about 75 miles for an independent Mercedes eval. Anybody come accross this before? Suggestions?

thanks

Kevin
1978 300D
1979 240D manual

[Diesel911]

If you can hear the sound while it is ideling; get an old broom with a good stick, cut off the broom head, open up the hood and and use it as a stethoscope . Put one end (do not get it caught in anything that is moveing) on whatever you want to hear the noise from and your ear carefully against the stick. Probe around with it until you hear that bad sound and identify where it came from.

[yellowbenz]

Originally Posted by Diesel911

If you can hear the sound while it is ideling; get an old broom with a good stick, cut off the broom head, open up the hood and and use it as a stethoscope . Put one end (do not get it caught in anything that is moveing) on whatever you want to hear the noise from and your ear carefully against the stick. Probe around with it until you hear that bad sound and identify where it came from.

I'll give it a try, but the sound is not coming from the engine compartment. It's clearly from under the car more so on the driver's side of the transmission.

thanks

Kevin
1978 300D
1979 240D manual

[rrgrassi]

I had a Chevy with the TH350 auto that started doing that.

Turned out to be a failing Torque Converter.

What is the level and condition of the tranny fluid?

Also, power steering pumps get noisy if they are running low.

[yellowbenz]

Originally Posted by rrgrassi

I had a Chevy with the TH350 auto that started doing that.

Turned out to be a failing Torque Converter.

What is the level and condition of the tranny fluid?

Also, power steering pumps get noisy if they are running low.

Thanks for the reply. The fluid is pink and proper level checked with the car at operating temperature. It does sound like it is forward in the transmission in the area of the torque converter. Say for the sake of argument it is failing, is there anything preemptively to do about it or should I just drive it and prepare for replacement in the future?

Thanks

Kevin
1978 300D
1979 240D manual

[Bill Ladd]

The used transmission I put in my SD made that very same noise just before it grenaded.

Not sure what went bad -- sent the tranny back from where I got it for warranty replacement.

Soon as the report back with the problem, I'll post here.

[TX76513]

Just another thought - look at your transmission just below the front support bracket is the transmission scraping their? A bad motor mount will allow the transmission to touch. When in the upper RPM.s the engine torque keeps it elevated unless you hit a dip in the road.

.02

[Diesel911]

Originally Posted by yellowbenz

I'll give it a try, but the sound is not coming from the engine compartment. It's clearly from under the car more so on the driver's side of the transmission.

thanks

Kevin
1978 300D
1979 240D manual

You have a gold mine in the fact that it makes noise at idle. It gives you a really good chance of finding where where the sound is comming from. usually it is the other way around you hear the sounds when the car is moveing and when you get out you cannot hear it.
Put your car up safely up on some jack stands; get under and listen again; you can still use that broom stick to listen with.
Lastly sounds are deceptive the hood padding and the fire wall often block sound comming from the engine compartment and it sounds as if it is comming from under the car.
What ever you find please let us know.

[rrgrassi]

Tranny fluid should be bright red, not pink. Pink indicates contamination by water.

[yellowbenz]

I checked it again today and it's red, I think the pink color was from the bright sun when I checked the first time. Would anyone recommend putting a floor jack under the oil pan, gently jack up the engine while running to see if the noise goes away? This would be testing the theory regarding motor mounts I hope.

thanks

Kevin
1978 300D
1979 240D manual

[Diesel911]

Originally Posted by yellowbenz

I checked it again today and it's red, I think the pink color was from the bright sun when I checked the first time. Would anyone recommend putting a floor jack under the oil pan, gently jack up the engine while running to see if the noise goes away? This would be testing the theory regarding motor mounts I hope.

thanks

Kevin
1978 300D
1979 240D manual

The pan on my Preowned car is a little caved in as if someone put a jack under it.
Find the thread on changing the motor mounts.
I believe it said if you put a piece of wood to spread the load over the whole pan (I am assuming the small steel pan) area before you use the Jack it would be ok to lift the engine off its mount to change the motor mounts (2 pieces of 3/4 inch thick plywood stacked togeather I think would do it and save them to use again).
Meaning it should also work for the purpose that you want.
Again it is best to read the thread and get the exact details.

[rrgrassi]

I use an 18" long piece of 4"x4" wood. No pan damage yet.