Help with vibration or rattle when accelerating from a stop. 1980 300SD Diesel

[WrightSounds]

Hey people,
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. 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 

[WrightSounds]

Here is a video of the noise: http://www.youtube.com/watch?v=IHIJ2IXuBhs&noredirect=1
You'll hear it three times, the first time being the loudest. At the end of the video I drive over a speed bump and the noise doesn't happen.
thanks,
Matt

[wbrian63]

My guess is a perished engine mount (one or both) that's allowing the engine to set too low, and also to move too much.

Here's how I test engine mounts:

1) Open the hood
2) Get in the driver's seat and start the engine.
3) Set the parking brake
4) Put your left foot on the brake pedal and press firmly.
5) Put the car in reverse
6) Keeping your left foot on the brake, apply the accelerator just a tad - you only need a few extra rpms above idle - 1000 to 1250 revs is sufficient.
7) Watch to see how much the motor shifts upward and to the left (I think that's the way it will torque in reverse)
Put the car in drive
9) Repeat steps 6 and 7, but now the motor will move upward and to the right (if I had #7 correct).

If the mounts are in good shape, you should not see very much movement at all.

Perished mounts will allow a lot of movement - more than an inch and possibly as much as two inches.

The reason why you don't hear the noise when you release the brake and idle away before adding throttle is much less torque is being transmitted to the drive line to accelerate an already moving 4,000# car. Adding throttle off the line transmits a lot more torque.

Regards

[WrightSounds]

Thanks for the reply Brian. I did your suggested test and my newbie eyes thinks they're fine. You were correct in the direction of the shifting motor. It moved a little more when in reverse than it did in drive but it didn't move much. It does move a bit when I turn the engine off. Kind of a duh-duh-duh, left/right/left movement. No knocking, just a shake or three 

Here are a few pics of the mounts:
http://www.flickr.com/photos/portlandguitarrepair/9417086361/
http://www.flickr.com/photos/portlandguitarrepair/9419853804/in/photostream/ (this pic shows some stress marks on the mount)
http://www.flickr.com/photos/portlandguitarrepair/9417086481/in/photostream/

I've had motor mounts replaced in a Hyundai and Mazda so I'm a little experienced with how collapsed ones behave under load. My gut is telling me it's not the mounts but my gut doesn't know anything about cars 

[andyatcrux]

It is hard to tell from the video, but I know that a little air in the fuel system will cause some injector knocking that will make a few rattling sounds when you first start the engine and sometimes after a few full stops. If you changed your fuel filters lately, this may be the culprit.

[Squiggle Dog]

It's possible for the engine mount bolts to loosen up and then the threads rub against the metal lip of the body. Mine were doing something similar, and when I looked under the car, one of the bolts that held the engine mount to the mounting arm had fallen out--but I could see that while it was loose, the threads of the bolt were rubbing against the metal on the body.

[ptashek]

My 450 made an identical noise after I have replaced the perished exhaust suspension rubber. The entire setup moved up and one of the pipe clamps was vibrating against the heat shield right where the downpipes enter the resonator.

[rob280sel]

what about your drive shaft rubber couplings?
Under load the rubber cant keep the yokes from coming together if they are worn.
My 280sel did something similar.