My vehicle:
1985 300CD-T (California). Transmission: 722.416
Issue:
The replacement vacuum box appears to be too large to fit into the transmission.

The part of this message having to do with the various part numbers is in the archives here but does not go into the issue of fit and concerns a 1990 model year vehicle.

Summary:
I made a post here about six months ago concerning a fluid leak at the transmission. The consensus was that the o-ring on the vacuum box unit was likely worn out. Suggestions were to replace the vacuum box (original) and its o-ring.

The M-B Electronic Parts Catalog (EPC) calls for part number 126 270 43 79 as the replacement vacuum box for my vehicle. I ordered this part and received the replacement vacuum box as a genuine M-B part contained in their box. The part number on the outside of the box is 126 270 91 79. The part contained inside the box has a part number of 126 270 57 59. None of these discrepancies would concern me all that much were it not for what appears to be the core problem: The replacement vacuum box appears to be too large to fit into the orifice from which the old vacuum box came.

I spent a couple of hours carefully seeking to work the replacement vacuum box into the transmission, however, it became quite clear to me that the replacement vacuum box was simply too large to fit into the transmission. The force that appeared to be required seemed extraordinary and I certainly was not willing to try and force the part in. The replacement vacuum box simply will not fit into the hole.

Perhaps the part number called for in the EPC is truly the right and only correct part number for my transmission and the replacement part is indeed the wrong one?

Does anyone have any ideas or suggestions or experiences with this situation?

Thank you-

I don't have the EPC but when I look at one of the parts places I use it shows
Modulator 1262709179 is supposed to have a Black Top for the 722.416 Transmission.
"For California models with 722.416 transmission group. For models with automatic transmissions. 1 per car."

Modulator 1262709279 is supposed to have a Green Top for the one that have a 722.315
'For Federal (non-California) models with 722.315 transmission group. Per Mercedes Benz supercessions this modulator replaces numerous earlier part numbers, vehicle listings are correct for this latest number. 1 per car."

So there is 3 questions.
What Colored Top does the Modulator you took off have and what is the part number on it?

Did you actually look at the Transmission Number on the Transmission?

It is also possible someone simply put the Modulator in the Wrong Box.

Take a look at the Pelican Part Numbers and compare them to Yours:
http://www.pelicanparts.com/catalog/SuperCat/3281/MBZ_3281_TRAUTO_pg4.htm#item15

__________________
84 300D, 82 Volvo 244Gl Diesel

The old vacuum box has a black colored top. I have attached three pictures of the old vacuum box here (Old vacuum box).

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The part number on the old vacuum box is obscured and unreadable after 29+ years under the car - who-da-thunk?!

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I have gone under the vehicle and checked the transmission number stamped on the right side just above the pan. It is as follows:
123 270 76 01 722 416 02184195

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The replacement vacuum box looks *much* different compared to the old one. I have attached three pictures of the replacement vacuum box here (Replacement vacuum box).
Notice that the replacement looks exactly like the picture at the Pelican Parts link you put in to your message. PLEASE NOTE: The red and white spots on the replacement are from me - I put them there to help me with orientation. The replacement did not have these spots when I received it new.

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This link is why I am skeptical that someone put the wrong vacuum box into the part box:
Transmission modulator 1990 300se w126

Attached Files

	Old vacuum box.pdf (494.5 KB, 85 views)
	Replacement vacuum box.pdf (600.3 KB, 84 views)

That how i got mine years ago. Bought it at the dealer. I havent installed it yet. Did you remove the old pin when you tried to install the new valve?

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

Since my second post in this thread, I have had the good fortune of discussing my concerns with a M-B transmission expert. Following are the results:

1. About part numbers
While it is true that the M-B Electronic Parts Catalog (EPC) calls for part number 126 270 43 79 as the replacement vacuum box for my vehicle, part number 126 270 91 79 is the replacement and current number. Furthermore, about the fact that the part inside the box has a part number of 126 270 57 59...the issue is this:
126 270 57 59 is on the housing of the part. This is the *housing* part number *only*. The entire assembly (including the pin [part number 126 277 86 75 - and note that the round-flat end fits into the replacement box] and seal ring [part number 014 997 11 48]) is collectively referred to as part number 126 270 91 79. This is *not* a matter of the wrong part being placed in the box.

2. About the replacement vacuum box fitting into the transmission or not
Answer: It fits just fine and as intended.
The surface of the cylindrical part of the replacement box that actually slides into the transmission should be lightly lubricated. Transmission fluid can be used but is not preferred. Wheel bearing grease is a good choice. Again, a very light film is to be applied.
All surfaces of the seal ring should be lightly lubricated.
The walls of the hole in the transmission into which the replacement box will go should be lightly lubricated.

3. Orientation of the replacement vacuum box
The vacuum port of the box should be pointing diagonally upward and toward the front of the vehicle (10:00 position if one was looking straight on at the box).

4. Orientation of the metal bracket around the vacuum box
The bracket fits on the *top* (not bottom!) of the box.

5. Other things
A. Clearance in this area is minimal.
B. Best to have the front of the vehicle on jack stands.
C. There is a front suspension bracket on the underside of the car in this area. Best to loosen it and temporarily move it to one side to help with access.
D. There are cables in this area. Best to use a bungee cord or similar to gently pull them out of the way to help with access.
E. When you are seeking to install the new box and all is properly lubricated, you should gently-firmly-carefully wiggle the box back and forth and up and down. This is what it takes to successfully situate the box into the hole. Ensure that the box fully seats into the hole.
F. Be prepared for some possibly nasty work removing the two 5mm hex screws that secure the metal bracket and thus hold the box in place. The clearance in the area is minimal. I used PB Blaster, heat (MAPP gas), time, and patience and my results were as follows:
i. The rear screw eventually came loose with a loud squeal.
ii. The front screw eventually stripped with the 5mm hex wrench. I had to grind down the sides of an easy-out (for clearance), gently but persistently tap the easy-out onto the screw's head, and then use a box wrench to loosen the screw. This is time consuming, very unpleasant, and harrowing work if you are forced to take this avenue.
G. One of those dentist mirror things that will swivel is essential for seeing what you are doing. I found one at Harbor Freight.
H. Be aware that the vacuum box does *not* fit into the transmission at an even perpendicular position to the side of the transmission or the floor. The box is tipped upward a bit toward the passenger side of the vehicle.
I. I suggest that you use some finger nail polish to make a mark on the box's cap and housing so that you can easily see where the cap fits onto the housing instead of guessing when you need to remove it and then re-install it.
J. The replacement box is *not* preset. For a turbo diesel engine, this is the way to properly adjust the new box:
i. Turn the key under the cap clockwise until it stops.
ii. Turn the key counterclockwise 6 turns.

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If the quality of all of the transmission shifts is acceptable, fine.
If the quality of some or all of the transmission shifts is not acceptable, vacuum adjustment can be considered.

What I did:
The first check should be done at the vacuum transducer unit (blue flying-saucer like part mounted in front of the brake booster unit).
On the top of the unit, there is a vacuum connection with the designation "TRA" (for transmission) next to it.
T into this connection your vacuum measurement tool (e.g., MityVac).
Operate engine at idle.
One should observe 15 inches of vacuum under this arrangement and condition.
Now disconnect the vacuum hose from the top of the white plastic vacuum control valve mounted on top of the fuel injection pump.
One should observe 6.5 to 7 inches of vacuum under this arrangement and condition.
If there is the need to increase or decrease the level of this vacuum, this is how it is done:
On the underside and at the engine side of the vacuum transducer unit, there is a port covered by a black plastic cap that is pointing downward.
Carefully pry off the cap.
Using your dentist mirror to look up inside this port, you will see a white plastic 4mm head screw.
Use a 4mm socket to adjust this screw:
A. Clockwise to increase vacuum.
B. Counterclockwise to decrease vacuum.

If all of the above is spot on, then the vacuum box key can be moved (and thus the vacuum adjusted at the transmission).
Remove the cover from the box.
Turn the key either:
A. Clockwise for a firmer shift.
B. Counterclockwise for a softer shift.

I made one counterclockwise turn and that was all that was needed.

Bottom line for all of this work:
Observe.
Be patient.
Think.
Easy does it.

For this job, your mileage, so to speak, may vary.