Hmmm... I wouldn't replace the transmission just yet.

Actually, you have a 4 speed auto and want it to shift into 4th.

I would first check that the vacuum line is connected to the modulator valve on the driver's side of the trans, and that the rod that connects the throttle linkage to the arm on the trans is in place

Then make sure that the lever is actually putting the car into D because S will not allow it to shift to 4th. This check is easy. You put the trans in N and make sure that you can get a pin (a large nail will do) all the way through the holes in the linkage case and arms. Then observe the linkage as someone moves the shifter through L-S-D-N-R-P.

If all this seems OK, take the car to a shop that understands the K4C transmission, and tell them that you want a service (complete fluid change, new filter, band adjustment) and your modulator checked and adjusted. This should cost less than $200. If they seem to not understand, don't use them.

If this doesn't fix it, then the trans needs serious work, and you should look into a rebuilt unit.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe