Hi all, I could really use some thoughts/advise on a transmission problem I'm having with my '84 300D Turbo Californian.

The backstory: A few weeks back I was experiencing some flaring issues so I thought I'd take a look at the vacuum system. Sure enough, I had a vacuum leak going to the modulator. But while doing this test I noticed that the previous owner had plugged up the vacuum going to the VCV. I replaced the blockage. At first the car ran just fine but then eventually I had more serious problems with shifting. 3rd or 4th would slip + other erratic shifting issues, until I noticed how low my ATF was. Filled that up, everything seemed okay, until I was on my commute the next day and the vehicle suddenly downshifted (must have been from 4-3, maybe down to 2). So knowing that I had the modulator leak I took my car into a shop to have it looked at. The mechanic replaced the modulator and then also re-routed my vacuum properly (I have a deleted EGR, so I wasn't sure how it should have been hooked up exactly). The vehicle now drives pretty great for the first 15 mins or so, then I won't be able to upshift from I think 2nd to the 3rd but maybe 3-4. One thing that bothers me a little is that the mechanic insisted on using 0.9mm orifices instead of what's called for on my diagram which is 0.5mm. Do you think this would make any difference? I've ordered some .7mm (the closest size I can find) and will try it out, likely next week. Could it be the K1 spring? My plan is to change the fluid/filter (not sure when it was done last) and slip in a new K1 spring. At one point through all this, I did smell some burning so I'm hoping I didn't damage anything beyond (easy) repair. One last note: When after my tranny starts acting up after 15mins of driving, if I disconnect the modulator line, shifting seems fine (and not even that hard). This is leading me to believe that this still might be a vacuum system issue.

Did the smaller orifices make an improvement?

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1985 300D Turbo CA Fed 223K

I doubt any kind of orifice will help with the issue. It is most likely a governor problem.

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'85 300D Cal 280,000 miles
'14 GLK 350 60000 miles

I will just relate what effect vacuum had on mine when I was fiddling with it, see if it helps clarify what your problem may or may not be...

Caveat: I have an '85 so it has the extra blue "UFO" piece that the transmission vacuum goes through.

I knew there was a vacuum leak on mine, that was slowly getting worse. I ended up replacing the hissing brake booster and that helped a lot, but the lines and connectors were still old. So I totally redid every connection under the hood.

Now it had great vacuum but the shifting was crazy soft, like really sliding between gears. I unplugged the UFO from vacuum and it shifted nice and firm, but perhaps a bit too firm at near-idle shifting. Next I connected it all back up but adjusted the modulator on the transmission a full two turns clockwise and finally it's shifting firmly but not jarring.

My theory is that the vacuum system was leaking for awhile so someone adjusted the modulator way back to soften the shifts. Or something catastrophic is wrong and someone is about to let me know that I put a bandaid on a grenade. LOL

BTW, what do the "orifices" actually do, anyway? I can't find any info, other than being a way to turn how the transmission shifts (presumably pre-UFO).

-Rog

My SD had a box on the valve cover with those little valves.The S shaped hoses were dust,I could not find them any where,so I removed the whole mess.Blocked off lines and run vac to trans only.Did that 10 years ago.

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1999 w140, quit voting to old, and to old to fight, a god damned veteran