I'm having problems with my trans in my 87 300d. I was messing with the throttle adjustment for awhile aka Bowden cable the white and black nut. Not exactly sure what I'm doing.

Since today I had extremely hard shifts and late shifts. I'm trying to figure this out before I throw the towel in and junk the car since it's been one thing after another. The fluid level is fine and not burnt.

It also shifts into 4th at like 60 mph or greater. I've turned the Bowden cable all the way in towards the oil filter housing and there's a decent amount of play.

Next I'll check the kickdown switch, but where else should I look?

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Only diesels in this driveway.
2005 E320 CDI 243k Black/Black
2008 Chevy 3500HD Duramax 340k
2004 Chevy 2500HD Duramax 220k

Vacuum system correct?

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Yes sir. Same setup as your 87 wagon.

__________________
Only diesels in this driveway.
2005 E320 CDI 243k Black/Black
2008 Chevy 3500HD Duramax 340k
2004 Chevy 2500HD Duramax 220k

The Bowden cable should be adjusted neutral...no tension, no slack. Adjust it back to the correct point, as it doesn't seem to be your problem.

What I would do is to temporarily patch a vacuum gauge into the modulator output of the BUFO. Then observe the vacuum level as you drive around. I'm guessing that there's a vacuum problem which will need to be traced out. Has someone fiddled with the modulator?

You can plug in the Mityvac between the VCV and the modulator and see what is happening with the vac. Just run the hose inside the front window and watch it as you shift. You should bleed down to about zero for upshifts and should have full vac for downshifts.

Adjust the Bowden cable back. It is for timing of shift and vac is for smooth shifting. Might spot your problem.

Thanks Frank. I guess I shouldn't be too worried its an internal issue, although I do have a delay in reverse. Always did since I got it. Think I could get away with using my mityvac as a vacuum gauge?


Thanks I didn't adjust the Bowden cable because I thought it was smoother. But because shifts were late and had a lack of passing power. Is the vcv the blue ufo?

__________________
Only diesels in this driveway.
2005 E320 CDI 243k Black/Black
2008 Chevy 3500HD Duramax 340k
2004 Chevy 2500HD Duramax 220k

Tyl604's explanation leaves a few gaps. Let me explain how this works.

BUFO=Blue UFO thingy. It's properly called a vacuum amplifier, sometimes it's mistakenly called a pressure transducer. It's not the VCV. If you call it a BUFO, everyone understands what you're talking about. It has four connectons, two on the top, two on the bottom. The ones at the top are full system vacuum (center), coming from the vacuum storage tank in the fender and the one on the side (which is where you want to T your mityvac or vacuum gauge) is the output to the transmission vacuum modulator .

The two bottom ports: the connection in the bottom center is T'd into the boost port on the side of the intake manifold. And the one on the bottom side is the proportional vacuum feed from the VCV.

The way the system works is as follows:

- Vacuum from the pump is fed to the VCV (which is on the side of the IP).
- The VCV has a variable orifice which feeds vacuum to the Bufo in proportion to throttle position ("closed throttle"=high vacuum)
- The BUFO reacts to the feed from the VCV and turbo boost pressure to feed an appropriately modulated vacuum signal to the transmission modulator.

What you're looking for at the vacuum modulator output is a vacuum signal that's highest at idle, and decreases as you apply throttle pressure. When boost cuts in or when the throttle is fully open, it should approach zero. There will be a blip when it shifts, but it's the vacuum level that's most important.

If you aren't getting a vacuum signal, you'll have to trace it back, and there are a few complications in this system, so it takes patience. You probably should hunt up a vacuum diagram for this car if you need to trace, as each year and model has it's nuances. You should do your testing with a fully warm engine, as some engines have a low temp thermoswitch near the thermostat that affects shift quality through a vacuum switchover valve, but that's more complication than you need to worry about at this point.

There was a great article on this, let's see if it makes it through the web police:

https://web.archive.org/web/20040211094849/http://continentalimports.com/ser_ic20242.html