...1987 300D Shifting Issue...
 

...I have a 1987 300D,...that seems to have a throttle pressure shifting issues...
...It stays in each gear way to long and sometimes will not shift into 4th without letting off the throttle...

...On the freeway it sometimes will downshift from 4th to third at freeway speeds without any change in throttle position...

...I do not know if the throttle pressure controlled by vacuum or electronically...and am unsure as to where I should start looking for the problem???...

Thanks

Kickdown switch.

Throttle pressure does not downshift ever, it only delays shifts. And when something goes wrong with the bowden cable (for throttle pressure) it usually does the opposite (shifting too early).

...Thanks...Do you have any idea where my problem might stem from???...

Try cycling the kickdown switch under the gas pedal, might become un-stuck. You can also un-plug the switch and see if your symptoms change.

...Thanks,...will do...

...I may have found the unwanted downshifting problem...A bit of the floormat may have been on top of the kickdown switch... ...When I first noticed it the car was carrying a passenger and 4 new TV's... ...It looks like the kickdown switch is realitively high anyway,...so I'm thinking I had the throttle further down than usual... ...No extra load no passenger and floormat moved that issue hopefully is solved...

...Initially I should have said that the transmission shifts very hard when upshifting... ...I had a restored 280SE 4.5 that you could adjust the hardness of the shifting by turning a key inside of a vacuum modulator... ...I am wondering if the same could be true for this transmission???...

...What is the Bowden cable???...

Bowden cable (AKA: downshift cable) determines the RPM of upshift/downshift.
Vacuum determines the harshness of shifts (with other contributing factors)
Kickdown switch modifies upshift/downshift points

The vacuum, and therefore the harshness of shifts, is modified by throttle position via the IP. If there is any loss of vacuum it will shift harsh.

The vacuum modification by throttle position is dependent on the engine producing the correct amount of power at a given throttle position. If the ALDA is not allowing boost enrichment or not getting boost from the intake plenum, there will not be the correct amount of power and the shifts will be harsh.