Hello everyone, I am new to this forum I just picked up a pretty good condition 300TD with the 722.416 transmissions and It has several issues with the transmission misbehaving. initially, the transmission would only shift at redline and shift so hard that it would chirp the tires from 1-2. I have since solved the harsh shift symptom by solving a lack of vacuum to the VCV and modulator as well as adjusting the modulator. However, I still have the issue of the transmission only upshifting by itself at redline/very high rpm. I have discovered that the Bowden cable does not have any effect on the timing of the shifts anymore which leads me to believe that there is something stuck or broken in the valve body.

The funny thing is if I quickly shift into neutral and back into drive it will shift into the desired gear at the correct speeds. Any help would be greatly appreciated.

Check for carpet causing kickdown switch to stick under accelerator pedal, defective kickdown switch or solenoid at the trans.

Key on RF door open, can you hear the solenoid click when flooring and releasing the accelerator pedal?

Good luck!!!

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Thanks for the info, I had already checked the switch and it functions as it should. I have just tested the solenoid with the ignition on and I can hear it click on and off. I may remove it and test it on the bench in order to make sure it is actually moving in and out but it seems that the kick-down switch and solenoid are unfortunately not my issue.

If this was a GM TurboHydramatic series I'd be looking for a stuck governor or one with a worn governor driven gear. The principle should be the same.

There are several forum members with much more transmission experience than me, hopefully they chime in quickly.

Good luck!!!

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Thank you! yea I have been doing some more research and I have a feeling it is either a stuck pressure control valve or a faulty governor. I just picked up a transmission pressure gauge kit and am going to check and validate that the governor, working, and modulator pressures are in spec. before opening up the transmission.

Side note: I took the car for a drive and tested the kick-down switch and it functions as intended. The switch and solenoid function correctly.

Any other ideas would be great appreciated from people more in the know than me.

How can you tell the kick-down switch functions as intended if you are only shifting at redline? Easy test. Unplug that switch and see what happens.

To clarify the transmission only upshifts at redline BY ITESELF. as stated in my orginial post when you pop it into neutral and back to drive it will shift into the correct gear far before redline which includes 4th gear. when in 4th gear I am able to manually press the kick down with my other foot(I am missing the throttle pedal and have to actuate it manually) and it kicks down correctly and smoothly. Additionally, I have checked the continuity of the switch and I have also tested the solenoid with the ignition on but the engine not running and it does actuate as intended. This was also confirmed by the correct function of the kick-down switch while driving as stated above. unplugging the switch was my first test which obviously made no difference so I dug further, thus me asking for any ideas.

bump

Do you have a spare car to swap parts from?
There is a LOOOOONG thread here about adjusting the vacuum on the transmissions.
I think it is titled everything you ever wanted to know,
Or the more than complete transmission thread… something like that.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

It's CRITICAL... how you set your transmission's vacuum system on your diesel MBZ...

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Thank you! I'll take a look at those!

Before you adjust the operating pressure of the tranny you must change the filter and ATF in both the tranny and torque converter .

Mercedes thoughtfully added a drain plug in the torque converter, you'll need a 5MM Allen tool .

After watching many fool with the vacuum I listened to an older Mercedes Mechanic who hipped me about changing the filter and ATF, Mercedes doesn't use a screen typ filter, it's a real filter that can and occasionally does get blocked by normal wear debris over time .

Once you have the operating pressure properly set it *should* upshift normally with the vacuum disconnected, then you can fine tune the shifting with the vacuum control valve on the injection pump .

You have an '85 so there may be some details you want to check before digging into this .

How about some pictures of the car ? .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Good to know! I already have a new pan gasket and filter for the transmission from Mercedes, which I'll install regardless, but I bought it because I figured if I was going to open up the pan, I should do it while I'm in there. As for the vcv adjustment, I performed the recommended tests and verified it is getting to the correct vacuum at idle, full throttle, and with the roller/coin method. I was under the impression that the vacuum system only influenced the quality/firmness of the shift and had no effect on the timing of the shifts. When I turned the modulator counter-clockwise a turn or two to see what happened I was able to achieve much more compliant shifts, just not at the right time.


I will be checking the working, governer, and modulator pressures this weekend and will report back with the findings. I will post some pictures after I wash it, as I realized I don't yet have any good pictures.


The last thing I should note is this is a 1985 CALIFORNIA car.

Once you get the fresh ATF and filter in there, disconnect the vacuum feed from the injection pump and adjust the modulator using a pressure gauge when the engine is fully warmed up with the car stationary on jack stands and engine at about 3,000 RPM, then you can peak and tweak the VCV on the IP .

Doing things in the correct order saves time and results in a better finished job .

I wasn't happy with how my '82 240D ended up shifting but my buddy the factory trained Mercedes Mechanic insists I leave it alone now because it no longer shifts from 1st > 2nd almost instantly like they did from the factory to increase fuel mileage .

In the case of the 240D, this means glacial acceleration due to upshifting at lower RPM's .

Now it's still only 67 HP trying to push a 3 ton vehicle so it's slow but it's also okay at keeping up with traffic, it wasn't before .

I did this same thing to my 1984 300CD and it has ZERO problems accelerating in second gear from less than 10MPH .

Everyone who's ridden in my 240D says it's perfect maybe so but I still miss that 32MPG's it used to get .

Once you have it all done you can add a vacuum gauge and test drive it and use a 7MM open end wrench to fine tune the VCV, you'll see .

As so often is the case, it takes TIME to do it really right and no shop is going to $pend the time .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better