Not exactly sure where this post would be the best place to put up so starting here due to the info included was garnered from a w220. There very well could be information on this posted already but i did a search and found nothing this specific. Figured i would share some info regarding the transmission electrical connector plug on the tranny for indexing into the greater merc community knowledge. Perhaps this could be of use to someone in the future. Not saying this is the be all end all, but it is the info i gathered from doing a recent tranny service. If you have data to suggest otherwise feel free to post up, but if you don't have anything constructive to add, please move on.

Ok, so this info is regarding the electrical connector/plug on the mercedes nag-1, 722.6, 5-speed transmission. More specifically regarding the w220 2003 s55. This info should be the exact same for all nag-1 transmissions no matter what vehicle it is in. Will most likely carry over to nag-2 and possibly further iterations as well. But someone far more knowledgeable than i would have to speak to that.

If one does any searching for transmission service on the nag-1 or 722.6 you will likely come across the notion that it would be prudent to replace the connector/plug when doing said service due to possible wicking issues if seal(s) break down. What i found out was that the supposed oe replacement part was not really up to the task of the original oem part. It is a little more fragile with seemingly less tolerance adherence. Almost a bit janky. Maybe that is all in my head but was not able to get the replacement part to work for me. Anyway, the reason i bring this up is that should someone ever wish to make sure the wicking issue doesn't happen to them, and are worried about a part that is perhaps not as well made as the original back in the day, then maybe the following measurements will help to save time and headache and a little money.

I took measurements of the plug and this should allow someone to source the replacement seals for less than a dollar. Yes, the plug isn't really that expensive to begin with. However, if you just want to source the 2 o-rings that should not be an issue with as long as your plug/connector is not broken or cracked. If you don't force anything is should come out fairly easily. There is even a built in pry point along the tranny and plastic collar to allow one to gently pry/slide the connector out of the socket. Well, at least to get it started. With a light on the part, and the lever in the down position you should be able to realize what i am describing just under/below the white level/tab on the rotating slide lock.....rotate up to lock down to unlock. There is a small lip on the black part of the plastic to pry against, and a tab on/near the tranny electrical port to work as a fulcrum for a flat head screwdriver.

Keep in mind these measurements where taken with my micrometer. I do not have schematics or proper manufacturer measurements/diagrams of the seals/o-rings. If the seal(s) you find are off by less than .2 or .3 i "think" you should still be ok with proper sealing of the unit.

Be sure to use viton o-rings. And don't forget to wet the o-rings with new atf fluid so help the new/renewed part slide back into tanny.


Smaller o-ring.....

35mm......this is the measurement on the connector where the smaller o-ring will seat/sit once on the connector/plug itself. So considered the OD(outer diameter) of the plug.

32mm(ID).....this is the INNER diameter of the smaller o-ring/seal before mounting on plug/connector
37mm(OD)....this is the OUTER diameter of the smaller o-ring/seals before mounting on the plug/connector
2.6mm(dia)....this is what is considered the 'thickness' of the o-ring before it is mounted on plug/connector(caveat: measured with micrometer so ranged from 2.5-2.7 depending on area measured and how lightly i touched the o-ring)



Larger o-ring.....

40mm.....this is the measurement on the connector where the LARGER o-ring will seat/sit once on the connector/plug itself. So considered the OD(outer diameter) of the plug.

38mm(ID).....this is the INNER diameter of the larger o-ring/seal before mounting on plug/connector
43mm(OD)....this is the OUTER diameter of the larger o-ring/seals before mounting on the plug/connector
3mm(dia).....this is what is considered the 'thickness' of the o-ring before it is mounted on plug/connector


Hopefully someone can find this info useful. Keep in mind the replacement part is only 15-20 bucks(did not look up what the dealer 'real' oem part costs) so you decide which way you wish to go. Seals can be had for under 1 dollar.

 

Would the ATF "wicking" occur thru one of the O-ring seal interfaces, or through individual pins, or between individual pins and the shell?

 

Good question. At first glance it would appear the base(pin connection throughput) is the source of the leakage/seepage. Matter of fact i too thought the exact same thing when doing the service. It is my understanding, based on very limited knowledge, that the external connector plug connects to the conductor plate inside the transmission, of which this particular part(at least the internal socket) is not exposed to transmission fluid. This understanding was garnered though feedback from others on this site. So take it for what it is....not first hand knowledge.

Edit: so to be clear it is my understanding the break down, or hardening, of a/the seal(s) is where the trouble can be found.