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82 300D, ISU Formula
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Ive been hearing and feeling this loud "clunk" as my transmision shifts as I come to a complete stop. Ive noticed it for a year now, but it has gotten progressively worse over time. The only time it occurs is when the car is cold and hasnt been running too long. Problem completly goes away after 10 minutes of driving or so. Transmission shifts flawlessly into any other gear.
 

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1985 Euro 300TD Turbo, 1983 Euro 300TD turbo, 1979 Euro 240TD and 1981 300D converted to euro.
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If it ever got hot before it might have left some crap behind in the filter? When was the last time you serviced the tranny and do you know if you are getting enough or tomuch vacuum to it?
 

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1982 300D,1986300E, 1991300TE AND GROWING
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I ALSO HAVE A CLUNK IT HAPPENS WHEN TRANS IS SHIFTING INTO 1ST ON SLOW DOWN. IM CHECKING MY FLUIDS.IN THE REAREND TRANS FLUID IS FINE. I WILL KEEP POSTED WITH ANY NEWS
 

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Mine seems to do that while decelerating at around 25 mph when the trans shifts out of top gear. After reading some previous posts on this site & on mercedesshop.com, I'm beginning to think it may be a vacuum problem stemming from those switches on top of the valve cover. One of them is for the EGR & the other affects the trans. A leaking switch or vacuum line, Paul.

1984 300CD Signal Red Ext. Black Int.
 

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That's a vacuum problem. Many people have needlessly replaced the transmission in their MBs due to entirely fixable situations like this. Work your way through the vac system with a hand pump. Replace all rubber hose connections as a matter of course. Get up under the dash and check the ignition switch vac connections. Check IP vacuum control valve for steady decrease from 15" to 0" @ WOT. In short, look everywhere for possible leakage.
Also, you may need to check modulator PRESSURE. There's pressure and vacuum at work there, be sure it's getting the pressure it needs. May need to pay a pro to diagnose this.
In my case I have a vac pod in the dash climate control that's leaking, causing clunking when I roll to a stop for a traffic light for instance. All I did was put a check valve on the line going from the engine compartment inside the cabin(just in front of yellow check valve) and it fixed the problem, but I only get A/C from the two side vents, not the center vents. Someday I'll pull the dash and fix it properly, but that's a huge inconvenience. It heats and cools so I don't care where the air comes from.
If you want to do some overkill on your car get some Redline Shockproof diff oil and put it in there, also some syth ATF and a fluid and filter change. Fix that vacuum problem and you will have a smooth shifter for sure.
 

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1982 300sd turbo
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daughter was cruizing in her 116 when she says tranny went clunk and will not go into gear,,,can see linkage is moveing shifting selector on trany as shifting , but no go,,,, foward or reverse,,,has me stumped[:(][:(] shifting lever moves to easy,not like when working,,shaft selector broke????thanks in advance for any help
n0rt[xx(]
 

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81' 300SD, 82' 300D
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N0RT75O - 5/22/2005 10:52 PM

daughter was cruizing in her 116 when she says tranny went clunk and will not go into gear,,,can see linkage is moveing shifting selector on trany as shifting , but no go,,,, foward or reverse,,,has me stumped[:(][:(] shifting lever moves to easy,not like when working,,shaft selector broke????thanks in advance for any help
n0rt[xx(]
Maybe shifter bushings?
 

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G320 & E500
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The first thing I would check is other vaccuum problems...
Do your door locks hold a vaccuum when you unlock the doors in the morning?
Does your engine shut down properly?
Are all of the flaps working properly on your A/C?

All of these things are signs of vaccuum leakage. Any one of these things can cause the engine to shift hard (or cause any of the other items listed to happen.

Chuck
 
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it must be a vacuum leak....i too have this problem, but only on occasion...........and i have new trans filter, Amsoil ATF, and she still does the clunk, sometimes. i thought its either vacuum related, or a bad rubber bushing somewhere.
 

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AMSOIL300CDT - 5/23/2005 10:40 AM

it must be a vacuum leak....i too have this problem, but only on occasion...........and i have new trans filter, Amsoil ATF, and she still does the clunk, sometimes. i thought its either vacuum related, or a bad rubber bushing somewhere.
This is going to sound hilarious... but get this...
When I had a vacuum leak in the doors, the engine would not shut off properly.
When you locked the doors. The engine would shut off.
 

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1982 300sd turbo
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got in touch with tech. today and he thinks its internal as no reverse and fluid is up,,,,,,think i'll swap out the motor and trany from mine as it has some rust issue's and will let me go ahead and look for a 123 ,,,,,,those 116 are famos for rusting out so is a good thing hers is in decent shape,,, mine was a little more rusted ,,,,will keep everyone posted on how it turns out[:D]
n0rt
 

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W-1-2-3 Go!
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For the clunk sounds, I have heard that it's sometimes the flex discs. I forgot where I read it, but that's what I heard. When I adjusted my transmission I noticed the clunk more, so I kept adjusting. It would sometimes make a sound but oftentimes it won't. So check the modulator and adjustment cables too, it might simply be in need of adjustments.

Nort, any word on the shifter bushings? If it's too easy to move those are the first ones I'd check. Goodluck!
 

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1982 300CD
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I made my transmission clunk, and then made it stop.

It involved the white transmission vacuum valve on top of the IP, next to the ALDA.

Here's what I did.

I took the unit off the car (two allen bolts and a clip), opened it up (two screws), loosened the nut, and overtightened the spring attached to the shaft inside. Then I tightened the nut, then put it all back together. It shifted hard, and clunked when downshifting into first.

Fixing it can be done while it's still on the car. To fix it, I took a 8mm socket with a short screwdriver handle, and carefully loosened the outer nut just a little. The inner spring loaded shaft loosened itself 1/4 turn. I then retightened it. Now it shifts smooth, and downshifts aren't even noticable.

It is a problem of not getting enough vacuum. Too much will make it flare. That valve is supposed to close, stopping the vacuum when the throttle increases.
 
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the white plastic part, where that vacuum line connects?

u probably cant make a pic, can u?
 

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1982 300CD
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I'm including a pic of the little bugger.

When you press on the throttle, linkage pushes a lever on the back of this part which turns a shaft which puts tension on a spring which in turn closes the vacuum valve inside. That valve cuts vacuum to the line which runs to the transmission modulator.

You need to have it just right. Too much tension on the spring and it will STAY closed all the time, making your shifts hard and clunky. Not enough tension, and it will never close the valve, making your transmission flare out between gears.
 

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remember back when i asked if i was missing a vac line? thats it right there....the round "connection", on the front face of it....
 
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maybe this valve is bad, causing my clunk, and my motor not shutting off.......ALL my vacuum lines are SEALED..........
 
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