Knocking sound (not engine)

[wagonhorse]

I have a 1985 300D Turbodiesel, while driving I hear a knocking sound that gets louder or softer as I drive at different speeds. If I stop and back up it either stops or gets quiet for a while. Pulled the tires of and found nothing wrong. Did find oil in the upper boot of the drivers side short shaft. Before I remove and replace the rear shafts is there anything else I could check. Also where can I find a diagram of the rear axel and drive shaft assembly.

1985 300D turbodiesel 270,000
1993 Chevy Suburban 240,000
1993 Chevy Suburban 4X4 240,000
2003 Pontiac Montana (Wife kid hauler) 160,000

[Outofworkjoe]

Yea look up at Resources,that's how I just replaced my axle using it.

[FLYWULF]

Hello,

I am not that familiar with the 300D but what you are experiencing sounds like a drive shaft carrier bearing that has either come loose on one side of it's mount or the rubber portion of the bearing assembly is just worn out and can not maintain the required pre load on the assembly. Almost all rear wheel drive German cars have a two piece drive shaft with a carrier bearing at the front of the rear shaft section. Some cars you can see it easily from underneath, on others you might have to take down a heat shield to examine it.

If you can get to it easily just grab a hold of it and see if it moves about. It should not move about, only the shaft should rotate. If the bearing assembly flops up and down check the securing hardware, it might only have loosened from it's mounts. Simply re tighten.

The rubber web is designed to give a little to absorb vibration. So it will normally move a bit when you tug on it.

If the mount assembly is tight then see if the shaft is loose in the bearing assembly. This would be caused by the rubber web in the assembly losing its resilience over time.

To replace it requires removal of the entire shaft. watch for alignment marks! Also note that if the shaft is not aligned correctly during reassembly it is likely that the symptoms will re occur but now only because the shaft was assembled incorrectly.

To replace the bearing usually requires a hydraulic press to remove and install the unit.

That is what I would check next it is a fairly common cause of what you are describing.


Cheers

EddiE

[wagonhorse]

As always I can depent in this forum. Some day I hope to contribute more.