I have a 1975 450SL that the heater works great, too great as it won't shut off without removing the vacuum line to the heater valve and blocking the valve closed. I found the levers, both drivers and passenger side, that are suppose to control the heat were slipping on the shafts. Looking into it further I found that the control shaft splits and controls an arm on the top side of the heater and one on the bottom side of the heater. It appeared that either the top side or bottom side was hitting something inside the heater, so I took apart the arms and found the top side free and working, however the bottom not going all the way into place (closed). I am guessing that by this not going into place (off position) it is not allowing the heater valve to close, thus keeping heat on all the time. I cannot see how or where anything could have fallen that far into the heater system to block the bottom flapper. Does anyone have an idea, or is this something for the MB shop?
Thanks