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  #1  
Old 05-11-2009, 10:24 PM
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300SDL: loud grinding transmission 722.321, noise in P and N position

I have lately some strange noises when I start in P and shift through N (in order to get to D). The sound is horrible and loud like grinding gears.
Other wise the car shifts great and drives great.
This noise is not always there but I had it several times now and I can't ignore it any longer. This sound scares me.

Reading in a manual I found this:
light grinding noise noise in 'P' and 'N' position:
"This condition is normal if a 'rolling' noise of front planetary gear is heard. If noise seems too loud, or if in doubt, a similar vehicle should be used for comparison"
I found this statement odd because it doesn't tell what causes the problem of the loud noise.
Another connection between P and N might be the starter lock-out switch?

Is there anyone in the forum who knows about this noise?
I'd need help.

Martin

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  #2  
Old 05-12-2009, 03:47 PM
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No one? Is there no one who knows this P and N grinding noise?
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  #3  
Old 05-12-2009, 04:15 PM
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If it Swims like a Duck...

Loud Grinding Noises signal self destruction to me...
(But,I don't have a 722.3 Tranny...AND when I did,it NEVER did that!)
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Old 05-12-2009, 04:21 PM
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I assume you are asking for "guesses" as there is no way to give you specific advice with that information. Check the easy stuff first - shift rod bushing and transmission mounts.
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  #5  
Old 05-12-2009, 04:27 PM
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Loud noises of any kind are often a bad sign in any transmission.
Did you check you linkage to see if the bushings aren't worn out or linkage is damaged? Is your transmission selector moving smoothly in all ranges?
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Old 05-12-2009, 04:59 PM
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Quote:
Originally Posted by lietuviai View Post
Loud noises of any kind are often a bad sign in any transmission.
Did you check you linkage to see if the bushings aren't worn out or linkage is damaged? Is your transmission selector moving smoothly in all ranges?

Noise is only heard in P and N- when the car is not moving at all. The car drives fine and shifts excellent without any noise as soon as it is moving.
This grinding noise doesn't occur all the time.
I think the noise is not there when engine is cold. But often if the engine/trans is warm.

I have checked the transmission fluid level and it was a bit high but nothing serious that could possibly cause this noise?
Transmission selector is moving smoothly. I haven't checked the transmission linkage. I will check his tonight.
Thanks for any input.
Martin
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  #7  
Old 05-12-2009, 05:04 PM
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Quote:
Originally Posted by TX76513 View Post
I assume you are asking for "guesses" as there is no way to give you specific advice with that information. Check the easy stuff first - shift rod bushing and transmission mounts.
I have not more information but will supply as much as I can.
I will check shift rod bushing and transmission mounts and report back.
Can the noise in P and N occur with a bad bushing and trans mount condition?
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  #8  
Old 05-12-2009, 05:04 PM
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Martin, hopefully it's shift linkage bushings. My SDL eats them.
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  #9  
Old 05-12-2009, 09:48 PM
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Relief valve noise? Front pump?
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Old 05-12-2009, 10:01 PM
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Quote:
Originally Posted by TX76513 View Post
Martin, hopefully it's shift linkage bushings. My SDL eats them.
I was under the car this evening and inspected the transmission. The shift linkage including bushings seems to be fine and so is the transmission mount- the rubber part at the rear end of the transmission.
Unfortunately I couldn't find anything that doesn't look good from the outside.
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  #11  
Old 05-12-2009, 10:06 PM
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Quote:
Originally Posted by babymog View Post
Relief valve noise? Front pump?
I don't know how the relief valve or the front pump sounds.

If it sounds like metal grinding teeth of a gear box (as if you shift with a manual transmission without the clutch!) then it is the noise I am talking about.

Again the weird thing is that the sound is only there in P and N position ...NOT when I am driving- in D the transmission sounds fine and it shifts nicely as before.
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  #12  
Old 05-12-2009, 11:53 PM
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Drain the tranny and torque convertor and then pour the fluid through a coffee filter and look for solids, (metal and fiber), then drop the pan and look for bigger pieces of the same. In this case more is not better.
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  #13  
Old 05-13-2009, 08:35 AM
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Quote:
Originally Posted by blindwolf View Post
Drain the tranny and torque convertor and then pour the fluid through a coffee filter and look for solids, (metal and fiber), then drop the pan and look for bigger pieces of the same. In this case more is not better.
Good idea. I am about to order a new filter and gasket- just in good hope that there is not much of any solids. I don't think that there are because the grinding is 'only' at idle in P and N for very short seconds. But who knows.

I am still questioning where this sound in P and N comes from and why it is not always there.

Just in case...If I can't get find any reason other that some inner parts of the trans are damaged what is my best choice:
1) buy a reman trans and install myself. What tools, how much time?
2) what is the best address/source for a reman transmission?
Martin
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  #14  
Old 05-13-2009, 08:44 PM
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ReMan Tranny

1.Mercedes may have one...Call a couple of dealers to compare prices.

2.A member here does ReMans, in Atlanta.
J. Hodgman of "Blue Ridge MB / AMG East" (404)-805-1357

3.OR, http://www.peterschmid.com/
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Last edited by compress ignite; 05-13-2009 at 08:51 PM.
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  #15  
Old 05-14-2009, 12:46 AM
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Its a grind

I am not a tranny expert but here is my guess. When the trans is in Park or Neutral the pump is disabled. No pressurized fluid is being supplied to the valve body or clutches. The only parts rotating are the converter and the input shaft and the gear attached to the other end of shaft inside the transmission. It sounds to me that the bearing that supports the input shaft is slowly failing and the wobbling shaft grinds the gear mentioned above against other components that are not rotating inside the trans.
If this is the case a complete rebuild may not be necessary as the worn component is at the front of the trans. You might be able to just have those components changed.

Thats my two cents worth

EddieE

87 300 SDL 325K

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