shift weirdness

Had some shifting difficulties with an '83 300D. Replaced the plastic shift arms. Now, shifting is erratic - sometimes perfect - sometimes rough. If I keep it floored, it's much, much smoother than if
if I go easy.
If I take it easy, shift points vary with the throttle position. In this case. the tranny usually will only stay in second gear for a few seconds before shifting into 3rd -- much too early. I realize this description isn' much to go on.
Any thoughts??
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I believe there are two issues to be investigated.
The transmission's shifts are coordinated with the throttle position. The older models have a "pressure" rod or cable from the (top rear of the engine) throttle linkage down to the right side of the transmission. At some point after '82, I believe, this was changed to a vacuum system. Your car is up shifting prematurely because its transmission isn't getting the correct throttle position message.
The transmission's shifts are modulated by a vacuum powered modulator whose vacuum supply is controlled by a throttle linked vacuum valve on the injection pump. The principle is: the greater the vacuum the softer the shift, conversely at full throttle there's no vacuum to the modulator because M-B wants a fast, hard shift.
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On Thu, 07 Apr 2005 16:00:30 -0700, T.G. Lambach wrote:

Excellent. Any ideas where I can buy or find a step by step troubleshooting guide for this subsystem?
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Thanks for the good info. I've had the same problem on my wife's 300D. When I drive it is simply hold the tranny in the gear I want until I reach the shift rpm that feels good.
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