240TD rear clunking sound

[grober]

https://www.startekinfo.com/StarTek/outside/12265/disc_2/program/Chassis/32-501.pdf
https://www.startekinfo.com/StarTek/outside/12265/disc_2/program/Chassis/32-670.pdf
READ THESE BEFORE ATTEMPTING ANYTHING!!!!

 

[martyz]

rubber doughnuts either end of prop shaft perished/damaged?

 

[sceh]

Like new - only done 75K miles

 

[sceh]

I think I have found the culprit!
I undid the levelling valve coupling to the torsion bar so I can operate it by hand.
With the engine running and moving the valve from the neutral position to either UP or DOWN, there is no movement on the suspension which means the struts are not under pressure which leads to knocking.
So...I now need to find out if it is the valve or the hydraulic pump which is duff.
Anybody done this?

 

[grober]

The first thing to suspect on these suspensions are the diaphragms inside the gas pressure reservoirs. The cars are effectively "air sprung" by pressurised nitrogen inside -separated from the hydraulic fluid by a flexible diaphragm-if the diaphragm ruptures or the gas pressure is lost the car is supended on its struts only which may cause the system to malfunction/ loose level control.

 

[sceh]

I changed them ten years (and 2000kms ago) so i have tended not to look at them. Since the car does not change height when I play with the SLS valve I am tending to look at the valve and pump. I could test the pump pressure if I had lots of money I suppose but I am thinking of simply taking the hose off to see if it pumps at all. If not, it is the pump. If so, it is the valve. Silly?

 

[sceh]

Could it be that the spheres have deteriorated and that the oil is being pumped into an empty sphere?

 

[alabbasi]

The little ball joints on the SLS shocks can cause a clunk, as can movement in the diff from a worn diff mount.

 

[sceh]

The little ball joints on the SLS shocks can cause a clunk, as can movement in the diff from a worn diff mount.


All brand new...

 

[grober]

Could it be that the spheres have deteriorated and that the oil is being pumped into an empty sphere?

I believe that's what happens when the diaphragm goes- usually precipitated by a loss of gas pressure?
Mercedes-Benz W123 Understanding Self Leveling Suspension | W123 (1977-1985) | Pelican Parts DIY Maintenance Article

 

[sceh]

The spheres are almost new and I do remember that when I changed them I could operate the SLS valve and the car would rise and fall but it does not seem to now. I need to check the pump to start with and wonder how I can do this without a rather expensive pressure tester. Since the oil goes to the valve at very high pressure and then returns to the reservoir when in neutral position, I wonder how it manages to drop from 100 bars to almost zero? I could disconnect the return line I suppose and should see oil coming out at the valve? This would show if the pump actually pumps but won't tell me the pressure.
Any ideas how I can test the valve as well?
I am guessing here but even if the spheres are duff, the car should still rise and fall although the ride would be as hard as hell since there is no gas cushion. Correct?