1990 300SE downshift clunk??? - Mercedes-Benz Forum

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post #1 of 14 (permalink) Old 06-07-2017, 01:52 PM Thread Starter
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Cool 1990 300SE downshift clunk???

Hey MB enthusiasts!

Just picked up a W126 from an acquaintance. At 244000 miles, the body and engine is in surprisingly good shape. I picked up a parts car for $160. I think I'm in love. haha

I've got a problem. I understand these cars start in 2nd gear. I hear a clunk and I am mildly jolted forward when downshifting from 4th(?) gear back down to 2nd gear. This only happens when I am coasting to 15 mph from 33+ mph to a stop. Downshifting from 3rd gear to 2nd gear is smooth as butter. Upshifts are fine, too

What I have done to avoid the clunking is to put my car into N and coast to a stop when I am in 4th. I know my car does not like that though, as my tachometer will drop from neutral idle of ~1500 rpm to 500 rpm, then to a stable idle of 700 rpm when shifting back to D.

If there is FGS I don't know about, this changes a lot of things. Should I check for this? There are no vacuum leaks.

Any suggestions?
-JC
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post #2 of 14 (permalink) Old 06-07-2017, 03:11 PM
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U joints , drive axles, flex disks , would be my first considerations.

Does it clunk going from drive to reverse and or reverse to drive?

Have someone listen to you shift from drive to reverse with your foot on the brake , if one side is louder than the other its a drive axle , if it sounds centered it could be u joints flex disks or but i doubt it the differental.

Not outside the realm of possibility the tranny mount of differential mounts.
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post #3 of 14 (permalink) Old 06-08-2017, 04:21 AM Thread Starter
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Quote:
Originally Posted by Richter Rox View Post
U joints , drive axles, flex disks , would be my first considerations.

Does it clunk going from drive to reverse and or reverse to drive?

Have someone listen to you shift from drive to reverse with your foot on the brake , if one side is louder than the other its a drive axle , if it sounds centered it could be u joints flex disks or but i doubt it the differental.

Not outside the realm of possibility the tranny mount of differential mounts.
Thanks!!! I will check and report back!
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post #4 of 14 (permalink) Old 06-18-2017, 06:14 AM Thread Starter
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Can I use a decent condition rear flex disc sourced from my parts car to replace the front flex disc on my main car??
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post #5 of 14 (permalink) Old 06-18-2017, 10:28 AM
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I would say ONLY if both flex discs (F and R) are the same part number and (more importantly) if the flex disc has absolutely no cracking in/on it.

While you're at it, take a minute to fill in your profile, "UserCP" at top of the page. It helps us help you, especially with having you car model there so we don't have to scroll back and forth to remember what you have (some of us here have memory challenges ) your general location is a plus too, never know, one of us might be just around the corner

Some days it's just not worth chewing through the restraints
My Stable:
'91 560SEC "Ursula"
'91 300SE (sold) "Sadie"
'98 Yota RAV4
'02 S-10 Truck
'72 SeaBird boat, "Riff Raft", overhaul restarted, will have new transom wood, new stringers and deck, plans are to upgrade to a V6 Chevy engine, virtually a brand new boat with a 45 year old hull

Dif-tor heh smusma I'm surprised that NOBODY has asked me what this is / means LOL
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post #6 of 14 (permalink) Old 06-19-2017, 11:53 AM Thread Starter
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Originally Posted by wooky_chew_bacca View Post
I would say ONLY if both flex discs (F and R) are the same part number and (more importantly) if the flex disc has absolutely no cracking in/on it.

While you're at it, take a minute to fill in your profile, "UserCP" at top of the page. It helps us help you, especially with having you car model there so we don't have to scroll back and forth to remember what you have (some of us here have memory challenges ) your general location is a plus too, never know, one of us might be just around the corner
thanks for the advice a genuine MB front flex disc is not that expensive ($65) on pelicanparts.com, so it'd be wise of me to install a new part huh....

while i'm down there, I should probably install a new transmission mount. the genuine MB is quite expensive ($235 ish). Should I purchase a merle tranny mount for around $15? Are there any better quality mid-priced alternatives?
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post #7 of 14 (permalink) Old 06-19-2017, 02:39 PM
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If you can find a Lemforder tranny mount I'd get one of those, I had to settle with a Meyle mount last year. A word of advise, stay away from anything "URO", junk parts that woun't last til the end of your driveway. If it was me on the flex discs, if there is any "iffy" I'd go ahead and put new, ANY cracks in the rubber is a "no go". Lemforder would also be good on flex discs, same with motor mounts, those I found and installed

Some days it's just not worth chewing through the restraints
My Stable:
'91 560SEC "Ursula"
'91 300SE (sold) "Sadie"
'98 Yota RAV4
'02 S-10 Truck
'72 SeaBird boat, "Riff Raft", overhaul restarted, will have new transom wood, new stringers and deck, plans are to upgrade to a V6 Chevy engine, virtually a brand new boat with a 45 year old hull

Dif-tor heh smusma I'm surprised that NOBODY has asked me what this is / means LOL
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post #8 of 14 (permalink) Old 06-21-2017, 07:34 PM Thread Starter
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Quote:
Originally Posted by wooky_chew_bacca View Post
If you can find a Lemforder tranny mount I'd get one of those, I had to settle with a Meyle mount last year. A word of advise, stay away from anything "URO", junk parts that woun't last til the end of your driveway. If it was me on the flex discs, if there is any "iffy" I'd go ahead and put new, ANY cracks in the rubber is a "no go". Lemforder would also be good on flex discs, same with motor mounts, those I found and installed
seems lemforder tranny mounts for a 300se are hard to come by. how about fortifying the two holes of the Meyle mount with silicon glue??
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post #9 of 14 (permalink) Old 06-21-2017, 10:12 PM Thread Starter
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Flex discs...

here is the front flex disc... not too bad????
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post #10 of 14 (permalink) Old 06-21-2017, 10:17 PM Thread Starter
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rear flex discs...

here are the rear ones. notice the cracks....
do you think these could be contributing to my downshift clunk??
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