Help with vibration or rattle when accelerating from a stop. 1980 300SD Diesel - PeachParts Mercedes-Benz Forum

WrightSounds · #1 07-26-2013, 04:47 PM

My 1980 300SD started to vibrate or rattle (not grind) from what seems like under the hood and in front of the passenger seat. It happens right when I accelerate and usually vibrates twice before it stops. I'm not feeling any vibration in the gas pedal or steering wheel. The car is driving, shifting very well.

ALL noises only happen after stopping completely and then accelerating. Once it's moving there is no noise. If I let off the brake and start to idle first before accelerating, it doesn't happen. It happens almost every time when I turn LEFT. It happens sometimes when I'm going straight and not yet at all when I'm turning right.

I recently repaired my air filter canister since the three mounting bolts had sheared off. I thought it my be that again by it's still nice and snug.

Any common things that it could be? My common sense says it's wheel related or maybe the brakes are sticking? I'm a car-repair newbie and while some stuff I'm fine with tackling myself (maintenance, minor electrical stuff, etc) most things are out of my comfort range and overall knowledge. Just hoping to get some ideas from y'all so I have an idea of potential problems before I take it in to a shop. Knowing is half the battle

ROLLGUY · #2 07-26-2013, 05:12 PM

Just grasping at straws, but could be a collapsed motor mount. I had a similar problem with one of mine. The two metal halves can touch each other and make a rattling sound like you describe. The weight of the engine will cause pressure to be added or subtracted depending on which way you turn, and make the noise only one way.

WrightSounds · #3 07-26-2013, 08:29 PM

Thanks Rollguy. They look good to me but I'm inexperienced. The rubber looks pretty thick and the metal above and below aren't close to each other.

But what is the circular mount-thing right next to the motor mounts? Are those shock mounts? Wow, whatever they are, they look like total $h!t. Like, non-existent. I'll take some pics by tomorrow and post them to the thread.

ROLLGUY · #4 07-26-2013, 10:02 PM

If you grab the valve cover and try to rock the engine back and forth (passenger side to driver side), you may be able to hear the sound you are having. If it feels very tight, then the sound is probably not bad motor mounts. Another way to tell is to have someone sit in the driver seat with foot on the brake and shifter in drive, and then you throttle the engine. Try it in reverse as well. If the engine moves a lot, then you have bad motor mounts. You will also hear loud and clear if they are bad.

sleepstar · #5 07-27-2013, 12:36 AM

check the condition of the exhaust mounts where it's attached to the transmission

rrgrassi · #6 07-27-2013, 01:54 PM

There are other things to check as well, like the transmission mount. Also check your flex disks and the center u joint and carrier bearing.

WrightSounds · #7 07-27-2013, 05:47 PM

Thanks so much for all the suggestions guys. I've got some research to do to find out where all those parts actually are

before I check them out

I'm going to record a video of it to see if it picks up the noise. Then I'll post that and some pics of my motor mounts, etc, for you guys to glance at.

Thanks again for the advice!

WrightSounds · #8 07-31-2013, 05:29 PM

Quote:

Originally Posted by ROLLGUY

If you grab the valve cover and try to rock the engine back and forth (passenger side to driver side), you may be able to hear the sound you are having. If it feels very tight, then the sound is probably not bad motor mounts.

I tried this and there wasn't much movement. But now I'm doubting my overall strength

I also checked where the exhaust is mounted near the transmission. That was solid and not loose at all.

Not sure where the flex discs are or the center U joint that rrgrassi suggested.

Here is a short video I made with my phone: 1980 Mercedes 300SD rattle - YouTube

You'll hear three similar noises, the first noise being the loudest. I'm making a left turn in the video. Toward the end of the video I drive over a speed bump but the noise doesn't happen again.

I've attached two pics of my passenger side motor mounts and one of my driver's side.

thanks again for any ideas or input,
Matt

ROLLGUY · #9 07-31-2013, 06:05 PM

Listening to the video, it sorta sounds like a bad center support bearing. You can easily check it. The rubber around the bearing should only allow the driveshaft to move side to side or up and down just a little. If the rubber is gone, the whole center support needs replacing. It also looks like your motor mounts are good, and the sound in the video does not quite fit a bad motor mount anyway.

WrightSounds · #10 07-31-2013, 06:12 PM

Thanks again rollguy! Right around :30 in this video, he's talking about what you're talking about, right? I'm heading out to take a look now!

Mercedes Benz 300D 300SD 500S 240D Driveshaft & Center Support BenzProducts.com - YouTube

ROLLGUY · #11 07-31-2013, 07:02 PM

Quote:

Originally Posted by WrightSounds

Thanks again rollguy! Right around :30 in this video, he's talking about what you're talking about, right? I'm heading out to take a look now!

Mercedes Benz 300D 300SD 500S 240D Driveshaft & Center Support BenzProducts.com - YouTube

Yes, exactly.

WrightSounds · #12 08-02-2013, 04:41 PM

Well I couldn't find it. I did familiarize myself with one of the flex discs, though (I'm learning part-by-part)!

Seems like I need to remove a heat plate/shield before I can get to the center support bearing? If I remove the heat shield will I be able to see it and shake the driveshaft to see how much play there is? I guess it's time to buy some jack stands since the 9" of clearance under the car sure doesn't help with seeing anything!

And does anybody have a diagram (or real life pic) of the driveshaft and exactly where the center support bearing is? I can't access the EPC thing because I have a Mac and it's not supported.

thanks!
Matt