Mercedes Benz repair: 1983 280 sl, modulator valve, writeup

Question
The automatic transmission will not shift into 4th gear.Could that be the modulator valve or ?

Answer
could be a modulator valve or the k2 spring in your transmission either way i would replace both here is a good writeup on a earlier transmission 190e
http://www.benzworld.org/forums/w201-190-class/1361737-diy-mercedes-722-3-722-4-...
just call the stealer and ask them which flare kit adjust from 3-4 gear i think it would be a k2
then mytis well replace them all and the tranny filter
http://www.benzworld.org/forums/w201-190-class/1360821-diy-w201-transmission-mod...
it is a different model but youll get the idea after reading