My sdl with >300k miles and unknown history with the tranny was shifting rough when purchased about a year ago. It wasn't bad, so i left well enough alone until i came upon a spare injection pump with vacuum controller. I swapped the vacuum controller, just on a whim, and the tranny began to shift much softer and more appropriately with relation to accelerator position. Over the next few months of driving, the tranny began to flare between 3-4, especially under heavy throttle, so i'd been taking it easy. Most recently, i drove the car on a 1000 mile round trip and it did well, except occasionally when exiting the freeway and decelerating on overrun, the tranny would sharply downshift from 4-3 and would not upshift into 4th unless the selector was moved to neutral for a moment and then back to drive, then it would behave normally. It did this 3 times during the trip, and it only occurred after extended highway driving. Now that i'm home, this has been happening more and more frequently, in fact, it does it more often than not, just running around town with no extended highway speeds. Is there a common cause for failure to upshift from 3-4 and a tendency to downshift from 4-3? The other shifts are pretty good, maybe a bit soft, but certainly acceptable. SHould i be looking for a replacement valve body? or is this beyond that point now? Any advice would be appreciated!

__________________
Patrick Frye

"Yeah, I'm crazy!!"

1986 300sdl
1982 300td

Gone but not forgotten:

76 240d
80 300td
81 240d - my first mercedes
81 300d
81 300sd
82 300td
82 300sd
83 300td
89 300sel

Drive it from a standstill with minimal pedal (slight downgrade is preferred).

Allow it to accelerate (slowly) and note the vehicle speeds for the 1-2, 2-3, and 3-4 shifts. Post results.

OK, so with the car at operating temperature, the 1-2 occurred at about 8mph, 2-3 at about 18 mph, and 3-4 was often stacked with 2-3, occurring immediately afterwards, so approximately 20 mph. This is a composite of several attempts. With a cold engine, the shift points were slightly higher, with 1-2 occurring around 12 mph, 2-3 at 22, and 3-4 not stacked with 2-3 and occurring around 28mph. Also, while cold, the shifts are firmer and occur more quickly. As the drivetrain warms, the shifts seem to take longer to complete and are softer. These readings were taken with minimal pedal pressure necessary to accelerate the car.

__________________
Patrick Frye

"Yeah, I'm crazy!!"

1986 300sdl
1982 300td

Gone but not forgotten:

76 240d
80 300td
81 240d - my first mercedes
81 300d
81 300sd
82 300td
82 300sd
83 300td
89 300sel

None of those speeds appear to be excessive, however, what I might attempt is as follows:

Find the Bowden cable terminus under the hood. It's just below and slightly forward of the oil filter housing. There will be a plastic adjustment knob on the aft side of the bracket. Turn this knob clockwise (aft looking forward) by two turns.

Take it for a drive again and see if it will stay in fourth.