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

VERY common failure in the early R107 SL's.

The flaps used FOAM for the hinges & that foam will fall apart & then the flaps will bind and then you can't shut the heater off. MB hasn't supplied those parts for over 15 years!
EVEN if they did you woud have to remove & disassemble the complete heater box to repair.

Best thing to do is disconnect the sliding rods for those flaps at the PINCH bolts on the heater linkage.

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Thank you very much. Since you mention the foam gasket, I do remember seeing them falling off the one under that dash that lets cool air in from behind the hood. Again, thanks for the help.
Doug