You may not be driving fast enough to get 4th gear. I don't think vacuum is going effect the number of gears.

__________________
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

I'm hoping that's the case. Tomorrow there will be new brake pads on it. Maybe then i'll feel comfortable finding fourth gear haha.

The peter schmid transmission diagrams for the 1985 model year is incorrect for the Federal version.
ALL Federal and California 1985 300SD 617.951 and 300D/TD/CD 617.952 share the same vacuum layout.



That switchover valve on the left of the brake booster is for the ALDA getting boost pressure from the intake manifold. It's #126 on the diagram.


.

__________________
1983 123.133 California
- GreaseCar Veg System

Thanks for the pointers!
The switchover valve is not hooked up in the place of #126 in diagram. It is connected to filter #85. The pic i posted with the arrow that says "from filter" is the tube coming from filter #85.
My switchover #126 is not there. A long tube goes straight from the banjo bolt of alda directly uninterrupted to banjo bolt in rear of intake. It's as if item #126 doesn't exist in diagram. I have been assuming it was removed, which i gather is common.

I need to explain a bit more. #85 is just vented, it does not need a switchover valve. That switchover valve is for Turbo Boost pressure. If not installed correctly in the transmission vacuum line circuit, you will have shifting issues.

Check out this thread. A member color coded the diagram I posted. Shown in post #2. Also look at post #13. It will explain how a 1985 transmission vaccum system works.
85 300d w123 vacuum ?'s with video - Mercedes-Benz Forum


.

__________________
1983 123.133 California
- GreaseCar Veg System

This is an amazing resource. Thanks for your whole contribution to the topic on that thread. It super clarifies things for me. This sets me up to tackle a few more attempts at digging through possible issues in the vacuum system.

As for the immediate items...

I will disconnect the "a" end of the filter 85 and make sure it is vented properly into the cabin. I wonder what impact that will have on the system. With it connected to the switch as it currently (mistakingly) is, I would assume the valve switch is just sitting there with air flow open at its bottom connection so it's not restricting open air flow to filter 85 at all. However it is engine compartment air instead of cabin air. So i will address it and send "a" into the cabin.

And i'm also not sure it will affect anything by adding the switch back in line between the alda and the intake manifold. Seems that is what many people choose to remove and without impact on performance other than losing the safety reduction of boost if it gets too high. Again it looks set up to simply pass air flow unless otherwise triggered.

But maybe the switch is faulty and it is currently blocking end "a" of filter 85 from getting any air flow. So possibly someone disconnected the switch because it was faulty and later on someone hooked up loose end "a" of filter 85 thinking it looked like it needed to be connected somewhere. And maybe having no open air at end "a" is having an effect on the system.

I will at least fix the "a" to cabin and we'll see what happens..

Wow, I just read the thread about the '85 model. Had no idea it was so much more sophisticated than my '81.

Interesting thread. Please keep us up to date.

Well i disconnected the "a" lead from filter and it's now getting air.

I don't really know if it's a huge difference, but i definitely noticed a more freeing feel of the ensemble of acceleration. I think. Maybe that's how it is when you begin a restoration from such a rough state. Every little problematic aspect contributes to slowing it down and when resolved it takes it one notch back to normal.
I took it all around some 40/45 mph roads with lots of hills. Only once did i end up feeling bad about the way it climbed a hill from standstill redlight. It started decently in 1st but when it shifted to 2nd it never got itself to a reasonable power and just churned up the hill. Ended up putting on my hazards to let the people behind me i was going to be a while up the long incline and that they were about to get a cloud. They backed off.

But that's how it used to always be every time. This time, for maybe 45 minutes of riding around, i had all sorts of success in various hilly and flat roads. Man this turbo is ruling my world. I still have the pressure gauge hooked up and when i start to get into the higher rpm's it's a beautiful push i receive. I always have to then back off the throttle because i'll start quickly speeding if not. Watching the pressure gauge i'm easily hanging around 8-10psi with throttle to spare.

I made it up many hills in D, and it seemed to follow the same pattern as if i'd started in L, shifted to S, and shifted to D. Except for that one instance above. However i've learned how to cater and time the throttle to hills in the car's condition. So I'd like to not have to do that so much.

But one thing is i still never got two gears in L. I get two gears in S. Shouldn't i be getting two in L and three in S? Max 2nd and Max 3rd?

I took it on the highway. There was a tremendous downpour of rain the whole time so the rain kickup on highway meant very poor visibility surrounded by 18 wheelers.

The good news is i felt very confident that the car has all the passing power i could want for a 300D. I was easily running right along at 70, in a cloud of rain/mist, and had to lay off the throttle to make sure i wasn't going to just zip right into the folks ahead of me. I do believe now that my turbo install, one of nightmarish proportions for a newbie, was 100% worth the four month downtime. And i don't think i could have refurb'd my old turbo successfully because the bolts holding it together were super rusted and brittle. One broke immediately, even after soaking for days in PB Blaster. I needed to steal a few bolts for my new turbo install since some studs were missing in back. Long story short, i needed this new turbo if i was going to make any improvement in boost, and i'm now so very glad that i did it all.

But i was still not hitting a fourth gear on the highway. The whole time i was cruising at 70mph i was at around 3000 rpm's. It sounded like the engine should be shifting soon. But due to the weather and traffic, i couldn't put it up to 80 or so to get it shifting. So who knows. But does 3000 rpm 70 mph seem like it should be ready to shift itself to 4th gear? I was expecting it to happen at any moment but it just kept churning along at high rpms. Still had lots of throttle and turbo left to go. I tried briefly playing with the throttle back and forth to see if it would kick up but it didn't.

So i'm excited but still feeling like it needs a full inspection of vacuum system.

In some ways, it seems like it's shifting too late, like on the highway. But in other ways it seems like it's not shifting down when it should when i'm going slowly. Almost like all shifting is delayed both when speeding up or slowing down. Or maybe we can just say the timing is all off and who knows what way. It needs to be tweaked.

But i wish i could have found 4th. I'm definitely weary of hitting 4000 to 5000 rpm's going 80 or 85, just to seek 4th. Is that potentially any sort of danger zone?

I had the shop do the brake stuff for me. It was the one thing i just didn't want to go through. They bled the fluids which took some extra work in the front, replaced the pads, and replaced one rotor per my judgement. They also discovered i needed the pins in the front replaced. I don't know if i would have discovered this. They also did the inspection so i'm good to go. i would have spent probably a week of off time digging through the brake stuff and dealing with acquiring parts and equipment and i have to draw some limits with my time. Plus that's the one thing i want done right for peace of mind. Wasn't that expensive. But now it's back to DIY.

Anyways i'm close.

3000rpm at 70mph is 4th gear.

__________________
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

OK.
Things are better than I realized. No wonder I was having so much fun even in the rain. I took it out again while it was dry and discovered that pulling that misplaced stopped up air vent lead had done a lot more than I sensed at first. I have no trouble getting up hills. I forgot that I had stopped at a gas station to do the vacuum pull, and that the rough hill was before that. All my driving after was better, and all this driving was better too. It had to be that vacuum issue. One air vent point does a big thing in the system I guess. Amazing.
Without the rain, I could see that there was virtually no smoke coming out rear when giving throttle up hills. I hadn't been able to see this in the rain. What a difference. It guns right up a hill when I ask it.
There are still shifting issues though. I can't get four total gears, or if I can, it's very mushed together or something. Or maybe it's stacked 2/3.
The shift timing is still a little wonky too. Gear A seems to carry on longer than I'd think it should. It really cranks and nearly sounds wild and then finally shifts. The shift itself feels healthy. It's not slipping or flaring or too soft or hard. It just seems like the timing of things is off all over.
But wow, what a relief.
I guess I should consider a full scale assessment of the vacuum system as the next step. Now that I thin it's established correctly, it needs tweaking. Who knows how long that line was mid connected and how many adjustments were made by someone trying to give power to the vehicle.
One related question.. how much PSI should I be considering a safe maximum in the turbo boost pressure readouts? 12? What about above that?

It's not clear to me how vacuum problems related to low power or lack of specific gears. Can anyone explain that?
There is a line from the ALDA to a second switchover valve associated with the vacuum amplifier. Would something associated with that reduce power?

__________________
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

The vacuum line in that particular circuit controls the turbo ARV and EGR functions. The unvented circuit effectively created a constant vacuum that forced the ARV to open up, decreasing pressure in the intake manifold and allowing the EGR to send more exhaust gasses into the intake. This unintended emissions combination will definitely reduce power.


Here is forum member Mach4's reworked diagram. It will show how #85/"a" is related to the ARV/EGR circuit.





.

__________________
1983 123.133 California
- GreaseCar Veg System

Now that i know what's been going on for who knows how long with this system, what do I need to do to make sure it's going to be running clean from now on? Does anything need to be purged? Any particular fluids? Any particular vacuum line tubes, filters or components that need special attention as in cleaning/replacement? Had anything maybe been damaged by the exhaust gases? And what about my new clean turbo? Have I been running this machine long enough to hurt it with this faulty setup?
It's worth mentioning that the previous turbo had tons of oil sitting in the front exposed tube shaped opening that connects via a wide plastic pipe to the air filter. I've seen videos stating this is blow by oil from the engine. But every time I've opened up this connection to inspect it with this new turbo it has been completely brand new looking still. Shiny silver.
Any chance that the oil that was sitting built up in old turbo was being caused by all the exhaust re-entering the intake because if this setup issue? And do I actually have blow by oil?

What's ARV? I can see how it connects to the EGR? How much does an EGR open all the time effect power? I've played with the EGR on my Land Cruiser, cutting it in and out of use. I didn't notice any power difference in that vehcile.

__________________
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

No chance that the firewall thingy has deteriorated and is not transmitting full accelerator movement to the injection pump is there?

- Peter.

__________________
2021 Chevrolet Spark
Formerly...
2000 GMC Sonoma
1981 240D 4spd stick. 347000 miles. Deceased Feb 14 2021
2002 Kia Rio. Worst crap on four wheels
1981 240D 4spd stick. 389000 miles.
1984 123 200
1979 116 280S
1972 Cadillac Sedan DeVille
1971 108 280S