Hello diesel friends. Long time since my last post - of which Forced Induction had great solution knowledge.

My 83 300d has 330K miles, and I am finally trying to tame the flaring shifts from 2-3 and 3-4 that have been there since I've owned the car (2002).

I just replaced the modulator on the transmission and the vacuum control valve that was not working at all. Now, the flaring is gone (the good news), but I have a hard shift from 1st to 2nd when accelerating and a very hard downshift into 1st when stopping. Of note, these hard shifts do not happen first thing in the morning when the car is cold, but appear once the engine is warmed up.

I could potentially tweak the modulator to soften the 1-2 shift, but am concerned this will re-introduce the 2-3 and 3-4 flares. Also, all the transmission fluid was replaced back in January when I had the main tranny seal leak fixed.

Any suggestions from you experts? Thanks much, BD

 

Update January 16.

I adjusted the VCV to 15 pounds (successful) then tried adjusting the modulator on the transmission. No matter which direction I tweaked the modulator (either adding or subtracting vacuum), there are once again flares 2-3 and 3-4.

Ultimately, I unhooked the vacuum line from the VCV to the transmission and plugged the vacuum end with a golf tee, after getting confirmation from 2 MBZ mechanics that this won't hurt the car. And with the vacuum line detached... shifting has improved greatly and likely as good as it's going to get - unless I rebuild the transmission which I have no intent to do right now.

Specifics: much smoother 1-2 shift, other shifts are super smooth and all without flare. The "hard shift" from 3-1 when approaching a stop I can pretty much eliminate/manage either by: 1) keeping my foot on the gas longer (with higher RPMs) prior to actually braking/stopping, and 2) manually downshifting from 3-2 the way we used to do with manual transmissions.

All in all, things are better. Odd that for all the views on my original post from a month ago, there were no replies from anyone else. Perhaps along with the 80's 300 D turbo W123 being well loved by me but a dinasaur and/or dying breed, there isn't as much lingering interest from the community as there was before. Just a hypothesis, not an indictment of anyone.

Happy New Year Diesel Fans!

 

Those "mechanics" are WRONG! You will destroy the driveline couplers from the shocks of shifting hard without it. I have done it.

 

Hi Just Aghost. Thanks for your input. Not sure I understand what you've posted. There is no long any hard shifting. What specifically is the risk and what happened with your car?

Thanks, BD

 

Without vacuum supply the transmission shifts as if you are at full throttle (as hard as it can shift).

 

Thanks for the input JustAghost. I ended up getting a shift kit installed with replacement springs for both K1 (2-3 shift) and K2 (3-4 shift). After properly being installed in the valve body, the flares have been eliminated and after hooking up the vacuum line again from the VCV, my car shifts great. No flares, no harsh 1-2 shift and smooth upon braking to a stop. I appreciate your guidance and hope this post is helpful for others dealing with transmission issues in their 300 Ds.