My catatonic auto transmission wakes up... sort of

[Zacharias]

Last year I had a thread going concerning (my own) used w123 240d transmission I swapped into my 1980 300td. The tranny had worked great in my 240d, but it had sat for about four years before it went into the TD.

The original trans was a vacuum-only unit, as was the one from the 1983 240d. If I recall correctly now, the original was a .118, the 'new' one is I believe a .117.

Long story short, once we got it into the wagon, it wouldn't shift into second. It would wind up in first and stay in gear (at least up to my tolerance point in terms of RPMs) unless you backed off the pedal... at which point it would slip into nothing. It would 'catch' into first again if you slowed down almost to a stop.

I changed the vacuum pump diaphragm to bring the vacuum up to proper levels. No change. I installed a new crossover valve on the valve cover (the white three-way valve). No change. I tried draining and refilling the fluid, and playing with the vaccuum modulator adjustment. Also completely disconnected the kickdown switch. No change at all.

I tried driving it for short hops though the summer, still no change. In the fall as a last resort I poured a bottle of SeaFoam into the trans, drove it a little, then parked it for the winter.

No change this spring. Other things had my attention all year, so the car only got back onto my radar last week. However, one thing did change: the car had been stored at my mechanic's lot, where I only had limited scope to drive it (stuck in 1st) due to traffic. Last week I towed it home, where I am able to drive it further at a time without fear of police attention.

Today I pulled the dipstick and realized that it was still way over full, from the SeaFoam. I slapped my head for having left it overfull all this time, and drained about 1.5 quarts -- then drove the car again.

NOW I HAVE SECOND, but nothing more.

First holds very, very high, until just about the single dot on the speedo (so nearly 25 mph). I've tried to get it just about to the two dots, but no signs of upshift beyond second.

What do I do now? Remember, this is a vacuum-only-control transmission. No Bowden cable, no throttle position lever.

I am inclined to add a little fluid (I overdrained a bit) and try adjusting the modulator....

[Govert]

You haven't described if the vacuum system works: have you done vacuum measurements? It should have full vacuum (22" Hg) going to the transmission at idle, drop to about 10–11" Hg once the switchover valve is actuated and drop to 0 vacuum at full load.

Vacuum modulator should hold vacuum.

BUT: even if you disconnect the vacuum line on a vacuum-only transmission, the transmission should shift—albeit only at the highest possible shift points—if it is in good working order. Same applies to the kickdown solenoid/switch. Your transmission doesn't shift at all from the first or second gear, that indicates something is wrong inside.

Putting a 240D transmission into a 300TD isn't adviseable, the transmission is adjusted to a specific engine, although I wouldn't expect that the transmission wouldn't shift at all because of that.

Have you changed the oil and filter? What is the colour and smell of the oil?

Could be a problem with the B1 piston. You can check the pin of the modulator too, it can break and cause problems.

Have you installed the torque converter correctly?

[Zacharias]

You haven't described if the vacuum system works: have you done vacuum measurements? It should have full vacuum (22" Hg) going to the transmission at idle, drop to about 10–11" Hg once the switchover valve is actuated and drop to 0 vacuum at full load.

The diaphragm and switchover valve were replaced when I was troubleshooting the failure of the original transmission (the diaphragm was torn and the valve was worn out, but they had nothing to do with the failure of the trans). I measured the vacuum when that work was complete and the readings were normal.

Vacuum modulator should hold vacuum.

Tested recently. It does.

Putting a 240D transmission into a 300TD isn't adviseable, the transmission is adjusted to a specific engine

I asked about that on this forum at the time and got no negative input on doing so... if that is the case, we're a day late and a dollar short on that score.

Have you changed the oil and filter? What is the colour and smell of the oil?

Yes it was changed when the trans was put in. What came out was clean and had no off smell.

Could be a problem with the B1 piston.

Is that possible, now that I have 2nd gear? If it is sticking, why only in 1st and 2nd?

You can check the pin of the modulator too, it can break and cause problems.

The modulator has been swapped once, just in case, and the one in there now has been adjusted twice. There doesn't appear to be any problem with it.

Have you installed the torque converter correctly?

The mechanic who did it has done MANY Mercedes transmission installs as he is located next to a large Volvo/BMW/Mercedes recycler and he does a lot of business installing used engines and transmissions for their customers.

I didn't watch him do it, but he certainly does know how it should be done.

[Govert]

Originally Posted by Zacharias

I asked about that on this forum at the time and got no negative input on doing so... if that is the case, we're a day late and a dollar short on that score.

It can cause problems with shift points, but it wouldn't cause a complete failure such as is the case with your transmission.

Originally Posted by Zacharias

Is that possible, now that I have 2nd gear? If it is sticking, why only in 1st and 2nd?

Perhaps it is not likely if there is also a first gear, although if there is something broken, it can cause unexpected problems. Could also be that a valve is sticking. The symptoms you describe (in first gear until very high, then only a second gear) resemble the L (or 2) position by the way. Is the shift rod connected and adjusted correctly? Perhaps the shift rod isn't actuating the valve inside.

Originally Posted by Zacharias

The modulator has been swapped once, just in case, and the one in there now has been adjusted twice. There doesn't appear to be any problem with it.

The pin was glued into the modulator?

Did you do the adjustment with a pressure gauge connected to the transmission? You can check three pressures (working pressure, governor pressure, modulation pressure) to see what is going on inside the transmission.

[Stretch]

Originally Posted by Zacharias

Last year I had a thread going ...

Re-reading that thread from last year and the other one you had going at more or less the same time has brought back the memories!

Those threads (and your problem) along with the teachings of Yoda Govert have lead me to believe in measurements.

Those threads (and other threads started by others since that time) demonstrate to me that it could be this - it could be that - it could be the other - it could be lots of things but nothing is certain with out a measurement.

Measurements are everything with 722.0 <=> 722.4 transmission problems - adjustment without measurement appears to be very hit and miss. You can't disregard the chance of good luck but you can't rely on it either.



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Scrub out all that I've said about your problem to date!

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Do yourself a favour - drain the transmission and the torque converter and measure out with great care the correct amount of fluid - the refill the transmission.

Then get some gauges and make some hydraulic and vacuum measurements

I'll post up some pressure data - you've now got a 722.117 fitted right?

[Zacharias]

Originally Posted by Govert

Could also be that a valve is sticking.

That's been my hunch all along, given that I knew the history of the unit. That is also (in part) why I've left it so long, while I tried driving and snake oil, rather than install another one -- which is almost impossible to find around here... only source wants $900(!) for a used one. I know someone who runs a small VW diesel shop and buys rusty old Mercedes to part them out, but everything he has right now is w126s (or another 240d trans, which I'd like to avoid now doing a second time).

The symptoms you describe (in first gear until very high, then only a second gear) resemble the L (or 2) position by the way. Is the shift rod connected and adjusted correctly? Perhaps the shift rod isn't actuating the valve inside.

Interesting idea, and the shifter is slightly off since the install, but nothing major.

However, if it were in L I would only have 1st, and in S I would have 3rd as well, wouldn't I?

The pin was glued into the modulator?

Sorry don't understand what you mean by glued. You mean was it put back in properly after adjustment? Yes I was there watching.

Did you do the adjustment with a pressure gauge connected to the transmission? You can check three pressures (working pressure, governor pressure, modulation pressure) to see what is going on inside the transmission.

No we haven't done that.

Thanks for all the input, by the way. This transmission peformed very well in the 240d, so I'd like to save it if I can.

[Zacharias]

Originally Posted by Army

Re-reading that thread from last year and the other one you had going at more or less the same time has brought back the memories!

And none good ones, LOL.

Do yourself a favour - drain the transmission and the torque converter and measure out with great care the correct amount of fluid - the refill the transmission.

The point being, to assess the amount of fluid, or to renew it? The fluid in there now is nearly all new.

Then get some gauges and make some hydraulic and vacuum measurements
I'll post up some pressure data - you've now got a 722.117 fitted right?

I believe so, it's been a while since I checked the number (I tried to find that in my old threads and couldn't).

No hurry on this. I have time to drive it right now, but that's probably going to be it for now as we have the Canadian winter temps coming upon us here very soon and I have arthritis... and work outside. Can't be crawling under a car on cold ground... worked ten years ago, but now I'm 52 and it's right out.

The timing is very irritating... I wish it had decided to start to rebirth itself in July. The LAST thing I now want to do is park it for the winter with the problem one-third resolved.

By way of explanation, I was doing something else yesterday on the other car and wanted a break... so I figured I'd take the TD for a spin. Apart from my extracting some fluid, nothing was different than many other days when I took the car out. I am kicking myself that I didn't pull the extra fluid out earlier, however....

[Stretch]

I'm concerned that the fluid level isn't correct - that's why I say to drain and then refill it.

Here's the pressure data =>



Please note this is specifically for USA destination transmissions...

[Govert]

Originally Posted by Zacharias

Interesting idea, and the shifter is slightly off since the install, but nothing major.

However, if it were in L I would only have 1st, and in S I would have 3rd as well, wouldn't I?

In L you would have first and second gear, but the first gear remains engaged until the maximum speed of the first gear (first dot on the speedometer).

In S you would indeed have third gear as well, and the shifting would be normal.

Originally Posted by Zacharias

Sorry don't understand what you mean by glued. You mean was it put back in properly after adjustment? Yes I was there watching.

Below you can see a typical modulator, without the pin/plunger:



Before screwing it into the transmission, the pin/plunger should be attached to the modulator. The plunger should be glued to the modulator, so that it follows the movements of the modulator because of the variable vacuum.

[Govert]

Originally Posted by Army

I'm concerned that the fluid level isn't correct - that's why I say to drain and then refill it.

Here's the pressure data =>



Please note this is specifically for USA destination transmissions...

The gearbox is a 1983 722.117, so this data may not be applicable.

[Stretch]

Originally Posted by Govert

The gearbox is a 1983 722.117, so this data may not be applicable.

1983 - Were they still making them then?

We need WIS I guess...

[Govert]

The 722.117 was used up to July 1983 in the 240D and to end of production in the USA. From July 1983 the 722.404 was used in the 240D, but not in the USA.

[Stretch]

Originally Posted by Govert

The 722.117 was used up to July 1983 in the 240D and to end of production in the USA. From July 1983 the 722.404 was used in the 240D, but not in the USA.

Do you have the pressure date for the later models?

And where do you get the production data for these situations?

[Govert]

Originally Posted by Army

Do you have the pressure date for the later models?

And where do you get the production data for these situations?

The pressure data are also in the German WIS. If there isn't a specific country model with pressure data, the general data should be used.

By the production data I guess you mean the changeover year. It can be found in the German WIS in the information about the 722.3 and 722.4 transmission in the chapter "Einbauübersicht" (or similar).

It can also be found here:
Kategorie:W123
in the Getriebe section.

[Stretch]

Thanks Govert - I'll post up the general data as well for Zacharias later on today (after I've wound up Windows in the VM again)