I can hear the turbo but no boost?
 

This happened today after degreasing and installing a speedomter cable. When driving the turbo will not boost the car like it use to. I could hear s noise that sounded like the turbo. I would have it floored and it would slowly accelerate after about 2200RPM as opposed to when it use to go pretty good after 2200 or so. I could feel a slight tug then it would cut out. So when accelerating after 2200RPM's it would start to go like normal then cut out. It is a 1979 300SD.
Thanks
David

There is a line that goes from the very rear of the intake manifold up to a crossover valve on the left side of the firewall, then down to the ALDA. That is a pressure line that sends a signal to the ALDA to dump more fuel into the engine when the turbo has pressurized the intake. If it is pugged or otherwise disconnected you will get what you are descibing.
Most likely the line got knocked loose when you installed the new speedo cable. Trace the line and see. If it appears intact, then remove the banjo bolt from the rear of the intake and start checking for unobstructed air passage. It gets all gunked up at that bolt, then sometimes all the way up to the crossover/pressure relief valve.
Sometimes you need to clean everything there.

On the otherhand on my 85' 300D I have never heard the turbo whine as I assume is typical of any turbo powered vehicle. I do feel a slight surge though when I guess the turbo kicks in. I am only assuming that the turbo works as I am not sure how I would truly know otherwise. Additionally the turbo was replaced about 40K miles ago so that would bias my assumption further toward a functioning turbo in my car.