I just purchased a 1979 300TD. The rear suspension is extremely bouncy. I have been told that the air cells are the likely culprit. I know that one strut was replaced by the previous owner, because it was leaking.

I need to know if this is a likely diagnosis--I am certain that the air cells have not been replaced at least for the last ten years, and it is likely that they have never been replaced.

I need to know the details of the repair, and how I can change the hydraulic fluid and bleed the system, if that is required. I also need to know the location of the filter, so I can change it.

Any help wouuld be most appreciated.

bauersjo@soltec.net
Joseph Bauers

Joe,

I do not think this is your problem, which is good news if I am correct. I will share my logic and maybe we can stimulate some thought and conversation.

Suspension is a system of springs and damping. The springs absorb the inpact and the shock absorber stops it from bouncing forever (damping). I sounds like your shock absorber is bad.

The hydraulic leveling with the accumulator air bag can be easily checked out by throwing a couple of adults in the rear while the engine is running. If it "pumps up", you are ok.

I hope this helps and that you enjoy the car!

I won't say anyone is wrong, but the shock dampening takes place in the "air cells". If you place weight on back & car comes up that means that the leveling valve & pump are working. If the rear is very stiff, then "air cells" (accumulators) are gone.

Thanks for the clarification. So does Joe only need air cylinders or possibly the shocks too? How can he tell which part of the system has failed?

Thanks for your input guys. I am pretty sure the air cells have never been changed in the 21 years life of the car. I think I will replace them, then I want to flush and bleed the system. I assume in changing the air cells, there will be a loss of hydraulic fluid. How do I go about replacing the air cells, then flushing and bleeding the system with new fluid. I am aware that it holds something like 3.5 liters of fluid. One mechanic told me that just replacing the fluid is adequate, and that the system will bleed itself out by driving the car. Another advises a quick feed and bleed approach, where one person puts fluid in with the car running, and an assistant bouncing the rear of the car to operate the suspension. Your thoughts would be appreciated.

Joe Bauers

In most cases the rear shocks (strut legs) work the system pressure from pump against the pressure in the accumulators. Unless the struts are leaking or knocking real bad they should last the life of the car!! They start knocking because the accumulators leak(internal) & there isn't any dampening action in the system. Don't wait too long or you will need new struts as well.