Hoping someone can put some insight on an issue I’m having. Ihave a 2005 c55 with about 73XXX miles. The other week I was driving home onmanual mode using the paddle shifter, I then notice that when I downshift from 3rdto 2nd at a high RPM (over 2300 rpm) I get this loudticking/clicking noise from somewhere in the front passenger area, it’s almostlike its coming from the front passenger tire. It sounds pretty bad, it’s likea really fast ticking/ almost grinding noise that will last for about a secondor two. I thought that it had something to do with the front axle or suspensionbut I don’t feel any type of shaking or vibration inside the car whatsoeverwhen driving on full automatic mode. I have tried to recreate this sound bydownshifting from different gears and it just happens from 3rd to 2nd.I have no clue to what it could be, has someone here experience this before? Ishould also add that I have the 1st - 2nd jerk during cold start ups and goes away afterdriving for a while. someone else in this forum posted a solution to this and that’s replacing the PWM solenoid. Not reallysure if the PWN solenoid has anything to do with the clicking noise I hear. I hope its not time to rebuild the transmission cause that would suck!

 

If the noise is only happening when shifting, it has to be something with those 2 gears. But with only 73k miles it's hard to believe your trans could be going bad already? It just doesn't seem right. The only other thing I would think of that could make a grinding sort of noise would maybe be the differential but you would hear that all the time.

If you can, see if you can get a video of the noise it's making and post it here so we can be of more help. Also, if you have a second car to drive try not to drive the C55 to avoid further damage. If you have no choice, then take it to a certified repair shop to at least diagnose and then decide if you want someone else to fix or try to fix it yourself.

 

that's what I thought too.. but the sound doesn't seem like its coming anywhere from the transmission at all and its smooth on S and C mode. And if its the transmission I assume it would happen all the time when it goes on that gear but it doesn't. I'll try to get a video of it this afternoon and post it here.

 

Hard to tell without hearing it. I would check the headers and heat shields, maybe an exhaust leak or something is loose.

 

I just took a video of earlier on the way home from work. You can hear it clearly after shifting down from 3rd to 2nd. I don't know how to paste the actual video here but here's the youtube link..

 

Wow, haven't heard anything like that before. When was the last time the transmission fluid and filter was changed?

 

Last transmission fluid change was less than 10k miles ago.. I periodically check the tranny fluid since I bought the dip stick for it. It's always on level and the fluid is still bright, No burning smell.

 

Whoa, that sounds terrible! I have no idea what that could be, it's just like a quick grind and that's it? That's the only time it makes that noise?

 

What it kind of sounds like is when you are driving a true manual and you downshift into second but don't quite engage it all the way, release the clutch and the gears grind. Maybe it has something to do with either the flywheel or torque converter?

 

Another suggestion: if it could maybe be something wrong with the TCU programming and not engaging the gears properly in manual mode, maybe it's an electronic issue. I don't know where the thread is but try searching "Sneaky ECU rest" which I think should reset the TCU as well. If that doesn't work, try the full on reset by disconnecting the positive terminal from the battery, waiting at least 5 minutes, and reconnecting. If the problem is still there, then it's likely something mechanical and not electrical.

Just a few thoughts...

 

Yup that's it.. It doesn't happen on any other time.. Not even when shifting up on the same gear at the same RPM. Just seems to happen on 3rd to 2nd down shift. I should also add that if I don't manually downshift and just let it downshift on its own that it doesn't do it..

 

Sorry for the multiple posts but I keep thinking of other ideas after I already posted I am very scatter brained right now...

You say it's fine in C or S mode, try pushing the buttons while in one of those modes to engage the shifting, so you are shifting between gears but still in C/S mode and not full M mode (it's slightly different). Try shifting down from 3 to 2 while in either C or S and see if it still makes that noise.

Report back with all of the above and see what you can find.

 

I haven't tried it on C mode but I have on S and I doesn't do it.. its weird.

 

OK, so based on that info, that's telling me that your TCU is shifting between 3rd and 2nd gear as it should when in S mode, but for whatever reason when you're in M mode and shift from 3rd to 2nd, it's doing something different that's causing the gears to grind similar to when you F up a true manual downshift.

Try the ECU reset by disconnecting the positive battery terminal and waiting 5 minutes (I would wait 10 just to make sure). See if that works.

However, I will tell you I'm not sure whether or not that will reset the TCU. I know it resets the ECU and I would think it should reset everything but I honestly don't know.

Maybe I should search TCU reset and see if that is a thing

 

Another important question, is the car stock or has it had any sort of tuning done?

 

no worries man.. I could use all the help I can get on this one. I was going to take it into a indy mechanic here to get a price on swapping out the PWM solenoid but looks like I might need them to do a lot more..

 

Stock.. everything is OEM.

 

+1,

Looks like something gotta loose, insulation around the Exhaust manifold or (Exhaust around tranny area).,!

prefer to jack the car & see careFULLY...

ZAYED,,

 

Maybe you can't fully reset the TCU: https://mbworld.org/forums/c32-amg-c...une-issue.html

So if it is stock though, I wouldn't think the TCU would be a problem. I don't think it's something loose that's rattling because then it would happen all the time and not only in M mode.

 

yeah I don't think its anything loose, if thats the case then it should happened more often than none. but this issue only happens at a very, very specific moment.

 

Before spending $$$$, jack the car, take a shorty look, and try to move all insulation...

ZAYED,,

 

definitely sounded like grinding... maybe something is hitting the driveshaft? (exhaust shield maybe?)
if I was you I would drop the pan asap and check the magnets... she might be done..

 

sorry for reviving a somewhat old tread - but has someone else here experience this before? I haven't been driving the car as much - I think I put maybe 2-300 miles in the last 3 months and car seems to be working just fine when I leave it at full automatic sport mode. I'm thinking of trading the car in sometime next year so I don't want to spend a whole lot of money rebuilding the tranny.

 

Finally got a chance to take the car in for a proper diagnosis and results were not good.

Can't believe it - I've had crappier cars last longer than this mercedes.

I called a few trans rebuilders in my area and their quotes range from $2200-4700 depending on what they find when they open this gearbox.

 

Uhmm.. I might have spoken a little too soon. Shortly after writing my last post above I was sitting in my living room looking at my bank account trying to figure out how I can afford this transmission rebuild and gave up not long after..lol since I couldnt find anyone in this forum that has similar issues to mine - I did a google search out of boredom, "tiptronic transmission grinding". One of the first things the popped up from the search was a Porsche forum. Looks like somebody with an expensive 911 is having similar issues with his tranny. This person took the car back it to the dealership for diagnosis and it turns out that the fix was a simple ecu reset and all grinds are gone. At this very moment I remember something that happened my car as soon as I picked it up from the mechanic earlier today. The throttle response was a lot sharper than what I was used to and the transmission actually shifted a lot smoother and more crisp. Almost like what everyone here described after a successful ecu reset. So I'm sitting on my couch thinking the mechanic this morning might have reseted my ecu while working on the car and could it be that my issue could possible have gone away just like the Porsche guy? I said no way a simple ecu reset could could fix anything mechanical. Well let's just say that curiosity got the better of me and I decided to take the car out for a spin. I put the car on manual I tried downshifting at from 3rd to 2nd at 2.5k rmp (where I would previously experience the grinding noise) and it downshifted PERFECTLY with no grinding noise whatsoever. I said this can't be true - so I tried downshifting at a even higher rmp 3.5k (previously this would also trigger the grinding noise) no grinding noise - just crisp gear change and sharp throttle response. So I drove around block a few times downshifting and up shifting aggressively at different gears trying to recreate this grinding noise that has haunted me for while but the only noise I heard was the rumble of the 5.4l v8 under the hood. Went back home, sat on the couch and pondered on what just happened the last 15 mins. I still couldn't believe it so I got back in the car and took her for a spin for a second time and I still can't replicate the grinding noise no matter How shift manually...... I still have my doubts about this simple and unintentional fix but for now everything seems to be working good and I guess only time will tell. I'll call the shop tomorrow and ask them exactly what it was they did to my car when they had it and I'll keep y'all's posted.