lewylou78

I recently discovered a very noticeable knocking sound that occurs whenever I let go of the clutch (fully) during low speed shifting (in 1st & reverse gears). It seems to be drivetrain related and the vibration can be felt in the stick shift when I hold onto it. Almost feels like something is loose or there is a lot of play in the drivetrain. My car is new with a little over 300 miles.

I can even be traveling at very slow speed in 1st gear and when I let go of the clutch, you can hear the knocking. It's very obvious & loud whenever I let go of the clutch really quickly in 1st or reverse, it sounds like something is about to break. Also, when I shut off the car, the knocking sound is present just before the engine cuts out.

Even my mom and neighbor heard it when I was backing out and both asked me what that sound was. I said I didn't know, but it sure doesn't appear normal to me when I was able to replicate it on my own so I took it to the dealer where I bought the car from and they had some mechanics inspect it.

They tell me that it's completely normal (which I find hard to believe). They said there has to be some "play" in the driveshaft or it will snap. I guess the only way for me to find out if it's normal is to find another 6-spd manual in the area (which will be tough) and test drive the car. Either way, to me it's an issue and I almost wish I didn't buy the car now because this problem witll continue to bother me (even if it turns out to be normal).

Was just wondering if anyone here that owns a 6-spd manual has ever experienced the same type of knocking sound from the drivetrain as described above.

eminnet

I also have 6MT and about 21.000 km since October 2008 and never had such issue.

Crisqo

no problem here...

Sportstick

Nor here.......

Derspeed

Never noticed. Get a second opinion.

lewylou78

Hmmm, well I found a 6-spd manual near by and I will go check it out tomorrow to see if that car has the same issue as mine. I just hope I didn't buy a lemon.

Derspeed

You're still under warranty. Make them fix it until they puke.

kirillbenz22

same here no problems like that in first gear, dont worry im sure the dealer will fix it without a problem

lewylou78

Well, there was a new 2010 C300 6-spd that I test drove today and it made the same knocking noise as my car makes so that tells me its either normal or there is a problem with the manual transmission that Mercedes is not telling people about.

Even the sales guy at the dealer seemed stunned when I showed it to him. He said they will call Mercedes to see why the car makes the noise. They were saying it made that noise because it wasn't prepped, but I was like that won't change anything.

Are you guys letting go of the clutch quick enough in 1st or reverse gear? I thought it was just my car, but I confirmed it on another car today so it's not just my car. I'm now convinced that every manual C300 has this, at least every 2010.

C300Sport

Are you depressing the clutch while the trans is under load? either accelerating or decelerating. If so I would expect a little bit of slapping around in the trans. Otherwise, there seems to be an issue.

Sportstick

Could someone help you try to capture a video?

lewylou78

It happens as I let go of the clutch when accelerating in either 1st or reverse gear. If you baby the clutch then it is hard to detect, but if you drive a little aggressive, it's easy to notice. I found this out not by driving aggressively, but when trying to squeeze into a tight spot on a hill and I had to press/let go of the clutch many times while accelerating.

Spec_Davis

hey bro sorry to hear about your problem but my C300 6spd has no shifting problem. Maybe you need to break it in it only has 300 miles on it.

lewylou78

The other new 6-spd manual C300 that I drove yesterday was much smoother when shifting through all the gears, but when driven aggressively, it also made the knocking noise. That car only had 20 mile on it.

On the other car, even when I put it into 6th gear it was smooth. On my car, I always feel some type of vibration (through the shift knob) when shifting into 6th gear, it's been like that since I had it.

I think the rear tranny mount is bad/defective on my car (even though the dealer said everything was fine). I just ordered a new one and will replace it to see if that helps.

If the new mount doesn't help, then I will trade the car in for a new BMW, I'm not going to waste my time with this car because this problem will lead to other problems down the road.

Doanster

Sorry to hear of the problems. I don't notice any of the same symptoms. The only thing even remotely close is 2nd gear can sometimes be a bit harsher to engage vs the others, but certainly not anything alarming or occuring w/ regularity. How aggressive is your "aggressive shifting"? Are you banging the gears home, so to speak?

*You* ordered a new transmission mount or the dealer is replacing under warranty? If it's on your dime, it seems premature to do so IMO before getting a better diagnosis or getting more miles on the car.

Good luck and keep us 6MT owners posted!

lewylou78

It has nothing to do with shifting or driving aggressively. The knocking happens when you let go of the clutch pedal (all the way) very quickly. As for shifting into 6th and feeling vibrations, that happens during normal shifting.

Yes, I purchased a new tranny mount for $32 and will install it myself, screw the dealer. Two dealers told me nothing is wrong already, but if nothing was wrong then it wouldn't be happening like it does. I told them to inpsect the motor mount, but if you don't remove it, then you can't really inspect it can you? By showing the problem to so many people already, I'm sure I stressed the mount even more so I don't see it getting better, if anything it will get worse.

Sportstick

The great philosopher, Henny Youngman, told the following tale:

A man went to a doctor and said, 'Doctor, it hurts when I do this'. So, the doctor said, 'Don't do this'.

So, why do you let go of the clutch pedal very quickly?

lewylou78

I don't do it, it happened unintentionally. Honestly though, no matter how fast you let go of the clutch, it shouldn't make that type of noise.

RLE

This is out in left field but does the exhaust system have any excessive motion? Grab one of the tailpipes and see how much lateral motion it has which should be almost none.

Why do so many people have problems with New Jersey MB dealers?

The "maybe it wasn't prepped" excuse suggests that the car was loosely slapped together and the dealer prep process would discover all the loose bolts? BS.

lewylou78

I haven't looked at anything underneath the car yet. Once I get under there, I will look at the mount and everything around the transmission (including the exhaust). I just drove the car and I could here it during regular driving now so I'm 95% convinced it's the rear engine mount (tranny mount).

I almost laughed at the guy when he said it wasn't prepped yet so maybe that's why? He told me some automatics don't have all the gears working prior to prep. I don't know if that's true, but I just didn't think that prepping the car would change anything for a manual equipped car.

I did some research and Mercedes uses the same rear engine mount on all c-class rwd cars (C300 and C350), but maybe there should have been a more heavy duty mount for manual transmission cars since there is a clutch involved. I don't know, but I will get to the bottom of this when I come back from my business trip next Friday.

lewylou78

UPDATE: Turns out it's not the rear tranny mount making the noise, it's the driveshaft. It just has too much play in it. Don't know if a RWD car is suppose to make these types of noises, but I can hear it everyday now and it's driving me crazy....crazy to the point that I'm going to get rid of the car and get something else.

Spec_Davis

hmm... i will have to check for that noise myself Thanks Lew for the heads up.