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Discussion Starter · #1 ·
I'm getting a clunk in the drivetrain when I go between throttle on and off. I can notice it most prominently when the car is rolling slowly - a slight touch on the throttle, then release and it clunks in either direction.

From inside the car, it feels like it might be directly under me, which could place the problem at the u-joint/bearing at the center of the driveshaft.

I sometimes feel vibration as well, but I don't think the vibration is wheels or tires, because they would always vibrate at certain speeds, not sporadically.

The flex disks appear to be OK. But I can't see that center joint. The exhaust, and then a heat shield are in the way.

Is the u-joint a likely cause of the clunk, and if so, how easily can I drop the exhaust to get at it?
 

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Discussion Starter · #2 ·
I should mention that the car has 85,000 miles on it
 

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Sith Lord
72 280SE 88 560SEC 92 E500 6.0 95 SL320 14 GLK350
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Not sure about the V8 configuration, but you can remove the rubber joints that hold the exhaust in place.

Removing it entirely would be a hassle, as you'll have to disconnect the headers.
 

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Discussion Starter · #4 ·
So, if I just drop it at the back end, but leave the exhaust all connected so that it just sags. That might give me enough room to romove the heat shield and work around the exhaust.

I also realized that I'll need to get the rear wheels off the ground, rather than driving up on ramps, to be able to inspect it properly. If the wheels are free I should be able to turn one of the wheels back and forth to find out where the excess play is occurring.
 

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Sith Lord
72 280SE 88 560SEC 92 E500 6.0 95 SL320 14 GLK350
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Ideally, is to raise the car on a 4-points jack with all wheels in the air.
 

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They seem all different but on my 95, I have removed all driveshaft componets 3 times without removing the exhaust. I don't have a cat conv though. Even when I did I think I may have been able to get to all that stuff. Even with the cat I just had one flange on the crossover under the bellhousing that would need unbolted if I were to remove the exhaust to clear any part of the drive train. The rest is just hangers, if I recall. I did have to tighten some flex disc bolts when it was doing the same as yours. They did not look loose and they weren't really loose, just not tight enough. It was very hard to see where it was slipping on the bolts but it was. Tightened them with a 16", 1/2 drive, breaker bar and its never done it again. Though they have a torque spec and it is pretty critical, I personally prefer my own feel based on the size and type of bolt and what it needs to do.
Oh, and if you do remove the drive shaft, don't make the same mistake I did and not mark every point it comes apart WELL with something that won't come off. You want to align it at the exact same as it was. Plenty of good pics before you do anything is a good thing too with about anything you do on these.
 

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Discussion Starter · #7 ·
... I did have to tighten some flex disc bolts when it was doing the same as yours. They did not look loose and they weren't really loose, just not tight enough. It was very hard to see where it was slipping on the bolts but it was. ...
Thank you. That is very good to know. I will inspect the flex disks more thoroughly and try tightening them.
 

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Discussion Starter · #8 ·
I was able to ge enough clearance under the car, with ramps at front and one rear wheel off the ground using a jack stand. That allowed me to turn the rear wheel back and forth so I could see where the clunk is coming from.

Bad news, I think. The play is occurring inside the transmission housing. Everything else appears to be snung from the rear wheel, all the way past the front flex disc.

This sounds like its going to be expensive.
 

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I'd get it on a lift to check better. About any garage will do that. I don't know what method you used to check but if you find it really is coming from before the drive shaft I'd check the drive plate for breaks or loose bolts just because it's easy to check. It has a 2 bolt cover at the bottom of the bellhousing.
 

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Discussion Starter · #10 ·
I'd get it on a lift to check better. About any garage will do that. I don't know what method you used to check but if you find it really is coming from before the drive shaft I'd check the drive plate for breaks or loose bolts just because it's easy to check. It has a 2 bolt cover at the bottom of the bellhousing.
Alchemy, to clarify, is this drive plate between the transmission and the front flex disk? I usually associate "bell housing" with the housing over the torque converter at the front end of the transmission. If I understand you correctly, you are referring to a housing at the back end of the transmission, but not inside the transmission itself.

Speaking of bell housing: while I was under there I discovered some leakage at the bell housing that has the two rectangular rubber plugs ( I assume are to access a torque converter drain plug) it has never dripped on my garage floor, but the housing was damp with oil or tx fluid.

I have also noticed lately what feels like a downshift as I'm coming to a stop. Perhaps it is related to this clunking.
 

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Alchemy, to clarify, is this drive plate between the transmission and the front flex disk? I usually associate "bell housing" with the housing over the torque converter at the front end of the transmission. If I understand you correctly, you are referring to a housing at the back end of the transmission, but not inside the transmission itself.

Speaking of bell housing: while I was under there I discovered some leakage at the bell housing that has the two rectangular rubber plugs ( I assume are to access a torque converter drain plug) it has never dripped on my garage floor, but the housing was damp with oil or tx fluid.

I have also noticed lately what feels like a downshift as I'm coming to a stop. Perhaps it is related to this clunking.
No, the drive plate between the flywheel and torque converter. I used to call them flex plates because they are supposed to give there before other places. I have had loose and broken ones before but not on an MB.
I am apparently missing the "rubber plugs" on mine but there are 2 holes that I've used to turn the flywheel (with a large screwdriver) to tighten the 6 drive plate bolts. The only reason I said I would check there is because it's easy to take the 2 bolt cover off and look. Beyond that I dont know how the output drive in the trans looks or what it could be in the trans, if it is something in the trans. Myself, if I knew for sure that it was something in the trans I may see about removing a stuff on the trans output to see if I could see something without taking it out yet. Then if I needed to I would take it out and start taking stuff off of the output end. I don't think its very complicated there.
 

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Here are some forum links to my trans troubles and a couple manuals. It shows me removing it, fixing it, screwing it up and putting in a used one. Note that in one of those manuals it shows stuff you can do without removing the trans.
There are other more formal and orderly stuff on trans R&R in the forum elsewhere.
I'm personally not convinced yet it's inside your trans because a clunk is usually something else.

http://www.benzworld.org/forums/r129-sl-class/1533044-bad-atf-leak.html

http://www.benzworld.org/forums/r129-sl-class/1538697-722-transmission-repair-manuals.html

http://www.benzworld.org/forums/r129-sl-class/1539361-no-shift-no-upshift.html
 

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Discussion Starter · #13 ·
Thank you so much for those links. I didn't think to search the forums other than the R129. There sure is a lot of info
 
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