I have been tuning my vacuum system to resolve a hard shift, early shift and flaring. I have removed the lines to EGR, tuned my VCV and adjusted my bowden cable so it is shifting as good as I am going to get it. The only thing I have lost now is when I am in 4th gear, or any gear for that matter, when the RPMS are still low (2000) and I floor the pedal it used to bring me into a super drive or whatever you would call this. It would really give me some power and race the rpms when I needed it. I am not sure what you call this. But now, when I floor the pedal, it just slowly goes faster, no more flash of power. sorry for lack of correct terminology. I suspect the bowden cable adjustment may have caused it. It is nice to know you can kick it up a gear when you need the power, how do I get that back? And what it is called? Feels like superdrive or something to that effect. There must be a name for this.

Sounds like the accidentally disconnected the line on the boost control circuit which goes from the banjo bolt on the back of the intake manifold over to the boost sensor. That line can get brittle. Trace it out and see if it intact. You lose boost when it's disconnected.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

It sound to me like the bowden cable was adjusted so far that it won't downshift, even when it's floored. I've experienced this with a stretched bowden cable. Try tighten the cable a little (unscrew the adjuster a little) and see if the downshift comes back.

BOOST CONTROL. That sounds like the right terminology! LOL

So is the clear line coming out of the banjo bolt the boost line? Today, I removed the banjo bolt to see if it needed cleaning. It looked good so I just put it back on. There were holes in the banjo bolt, are they supposed to be aligned in some way when reinstalling? I will follow the line tomorrow to see where it goes. and check the connection.

Thanks.

See Craig's post, he probably has a better diagnosis if your problem is lack of a downshift.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

There is no specific alignment for the bolt, but make sure the entire line is intact and you didn't pull off any of the connections or break it. If the line is OK, try the cable adjustment.

Right on....took the bowden cable adjustment too far on my 83 300D. When I tightened it up, I got a bit harder shifts and my boost was returned. Guess its a compromise with older parts. I founds a happy medium.

Good deal, now that it's shifting in the correct spots, you can adjust the firm shifts with the modulator on the transmission. That will just make it shift softer or harder without changing when it shifts.

When I hooked up my mityvac to the vac line going to the modulator, after I pump the mityvac, it quickly drops to 0 with the engine off. I went under there and found the cap to be cracked all over. I ordered a new cap. Just to be sure it was not the modulator itself, I drove with the line to the modulator disconnected and got much harder shifts and a bang on the downshift so I think my modulator is working to some degree, just not getting enough vacuum due to the cracked cap. I will wait to adjust it until the new cap is installed. Thanks for the posts, i am almost there.

Sounds like you're on the right track.

The only oddity is that you describe both hard shifting and flaring. These conditions seem incompatible with each other. Hard shifting is caused by low vacuum and flaring is caused by high vacuum. So if both are happening in the same shifting sequence, I don't think both can be resolved by adjusting the vacuum one way or the other.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Yup, sometimes you have to live with hard shifts to avoid flaring (depending on the transmission condition). I did that for a while with my old tranny.

Got my new modulator cap today, put it in and tested with mityvac. It now holds vacuum as before it dropped right down. I was expecting miracles after replacing it but I think some additional tuning is still in order. If I accelerate slowly (1/4 pedal) it shifts great through all gears!!! If I give it moderate acceleration (1/2 pedal) I have hard/late 1-2 shift, a super early 2-3 (almost immediate) and a great 3-4. Where do I begin and at which component? I have not checked throttle linkage position yet...not sure exactly where to measure distance.

Questions to solve these issues:

Hard 1-2: Adjust VCV or Modulator? I believe (& will check again) VCV has a vacuum of 10 coming out the top. Should 10 be fine and how much acceleration should it take to get down to 5, and then 0? If VCV is OK, should I mess with modulator and turn 1 notch CCW to allow more vacuum or should I allow more vacuum out of VCV?

Late 1-2 Shift - adjust Bowden cable? Should cable be relatively taught or should i still be able to take the end at the socket and pull it out a couple inches?

Early 2-3 - also Bowden cable? K1 sping kit?

I rarely get boost any more either. I think I lost it when I dropped the VCV vacuum from 15 to 10, or possibly when turning the bowden cable. Is boost controlled via kickdown switch? If so, what does it look like and where is it?

I just wonder if this is as good as I am going to get it being its 25 yrs old. I am confident I have no more leaks, just not sure if I am going to resolve all problems or if i should live with what I've got. Sorry for the many loaded questions.....can you tell I am spinning in circles?

I have resolved all but one shifting issue on my 83 300D Turbo. No more flaring and have softened the 1-2. Only problem is I can not make the 2-3 shift on time. It always wants to shift too soon no matter how tight I adjust the bowden cable unless I accelerate very slowly. I did notice when adjusting my VCV to bring it down to 10 that it is super sensitive. I tried making it 8, but then all my shifts were hard. I found that making it 12 works best and avoids flaring. The only way I get great shifts through all gears is if I accelerate slowly with light throttle. If I step on it 1/2 throttle, my 2-3 shift occurs immediately. I am thinking my VCV valve is not working that great. It is inconsistent pending the pedal pressure. How do I test it?
I was considering replacing the VCV OR giving the K1 spring kit a shot to correct the early 2-3 shift. I just dont want to throw away $$ on parts unnecessarily.

__________________
1983 300D Turbo
265,500 miles

Plug a mighty vac to the top of it, as the lever adjusts so should the amount of vac it can hold. You may need a new bowden cable? Have you bypassed 3/2 levers?

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