Vintage Cars: 1987 Mercedes SL560, bowden cable, vacuum lines

Question
QUESTION: Hi Ron, I have a problem with the transmission on my 1987 SL560, it hangs on to the 1st & 2nd gears on the way up the box, longer than it should and it is very sensitive to the accelerator and will change down when you do not really want it too. I have renewed the modulator valve and all vacuum lines are connected. The sequence is as follows;
On pull away, I have to take the engine revs upto 3000 rpm and then let off the accelerator a little, then it will change to 2nd.
The transmission will not change up to 3rd on it's own unless I get to 60mph. However, if I get the car upto between 30 to 40mph at around 2000rpm and I flip the gear shift stick from drive to neutral and then back to drive quickly, the transmission will change up to 3rd. Can you give me an idea as to what the problem might be and suggest a way to fix it.
Michael


ANSWER: it sounds like a valve body problem to me too. On old transmissions, the buildup of varnish on the moving pistons (due to lack of maintenance - i.e. ignoring the fluid change interval) causes them to get stuck in place.
If you are sure the modulator is good, linkages adjusted and pulling normal vacuum AND you have changed fluid and filter and flushed it good then you may be in for a tranny rebuild
How many miles on it?
also as a long shot, You can try to disconnect the kickdown switch as a test, they sometimes will short out and cause this tranny to think it is always floored

---------- FOLLOW-UP ----------

QUESTION: Hi Ron, thanks for that, the milage on the car is 85k and the modulator is brand new. As far as fluid change interval, I have no idea whether this was maintained or not, so I will change the fluid and filter, what would I used to flush the system? I notice that you did not mention the 'Bowden' cable, would you reccomend adjusting this cable?

Answer
the bowden cable can cause late shifts, particullary if the engine mounts are worn, adjusting it to specs is a good idea, but I doubt it is your issue unless it is severly out of wack.  I would just drop the pan and change out fluid and filter<  I would disconnect the lines to the tranny cooler and drain.  If you really want to do it right rotate torque converter to find drain plug and drain as well.  Refill ( DO NOT OVERFILL) with high mileage tranny fluid.  Good luck