Mercedessource series on 722.3 Operation - Very Informative

[gerryvz]

The @gsxr's Uncle Kent has been creating a multi-part video series that details the internal operation of the 722.3 transmission. It is very very illuminating as to how everything works together to create the four forward speeds + reverse, and explains a lot of the issues with regard to our transmission problems -- specifically the reverse clutch and K3 wear, as well as external seals.

For best efficiency, view at 1.5x speed.

Here are the various videos in the series, so far:

 

[gerryvz]

 

[gsxr]

I just finished watching all the above videos. Overall, it's great stuff, especially for the transmission novice. @dionphaneuf - you checked these out yet?

A few comments:

1) Some items he shows are only used on early 722.3 transmissions, used in the 1980's and maybe 1990-1991. In general, most (all?) of the M119 transmissions from 1992-up USA model year, likely have the latest & greatest components. Specifically, the B1 piston should be the new auto-adjust type. This is totally different vs what Kent shows, having to manually measure & adjust B1 clearance with shims, on the 80's B1 in his video. And, most 93-up will not have the secondary pump. Kent says this was used to 1990 but AFAIK it was present up to at least early 1992 USA model years.

2) In the "End of Life" video, I disagree with his inference that a 722.3 with many external leaks probably needs a full rebuild. If it's leaking from multiple external seals, it absolutely needs a full external reseal. However, if it shifts perfectly, it may not need a complete internal rebuild, which is far more work. I do recommend pulling the transmission out for a full reseal, and the front pump has to come out as part of this reseal job... so at that point, new reverse (B3) clutch discs are highly recommended (and you'll probably find they are worn out anyway). You can also easily check the K1 clutch discs and at that point determine how to proceed. If band B1 still looks new (it should) and K1 frictions are not abnormally worn, there's a good chance K2/B2 may be fine as well - remember, we're assuming the trans shifts perfectly and only leaks externally. OTOH if you find K1/B1 has abnormal wear... yeah... rip it all apart like Kent says.

3) Just an FYI, the Genuine MB complete seal kit is NLA but the aftermarket Elring kit is available for $125-$150 from various vendors.

4a) I'm having trouble confirming if MB sells the "hidden" O-rings in the bottom of K1/K2 drums, or if those are an aftermarket-only item.

4b) UPDATE: The K1 "hidden" O-ring should be included in the master seal kit, and may be available separately (p/n TBD). However the K2 O-ring is not sold by MB and not included in the seal kit. This must be sourced separately, see post #7 below.

5) Late style K1 drums do NOT need to have rivets drilled out to replace the hidden O-ring. I don't know the production break point, but I suspect 1980's vintage need drilling/tapping, and somewhere around 1990-up should use a circlip to retain the lower support. So, you can replace the hidden K1 O-ring on most/all 034/036 transmissions without drilling/tapping.


The old Fruitbird forum has an excellent thread on the K2 drum "hidden" O-ring replacement:

722.317 K2 Drum Rebuild - PeachParts Mercedes-Benz Forum

I am in process of rebuilding my 722.317 Automatic transmission in my 1987 Mercedes 300D, 124 Chassis. The transmission has around 325,000. The speed-o

www.peachparts.com

 

[gerryvz]

I agree that it's a really nice overview of how the internals work. The cutaway transmission is genius, as well as how he operates it to simulate shifting of the gears, and the effects of pressure built into the system.

Also interesting that he is planning to take the valve body apart and do a rebuild video on that. Some of the special tools that he has created for transmission rebuilds (i.e. removing B1 and B2 piston covers) are nice repros of the factory tools, which are either NLA or prohibitive cost.

I definitely have the secondary pump on my 1989 SEC, but it is not present on my E500 nor my G-wagen. I do not believe the Elring kits include the bottom seals for the K1 and K2 pistons.

Just wanted to document all of this here in this thread as a reference for folks. There is actually a lot of information out there about 722.3 rebuilds (documents and such) and a few good HOW-TOs on MB forums, but it seems that transmission rebuilds have been -- on this forum -- something that few have attempted.

 

[gsxr]

Yes - I looked at his tool offerings, and might buy one or two. I have a 722.3 tool kit that does some of what his tools do, sadly I believe those kits went NLA years ago (must be no demand in the aftermarket).

The valvebody work is primarily cleaning. Nothing really to "rebuild". The vast majority of springs are not sold separately (except K1/K2 spring trains). The Teflon seals on the plastic pistons can be replaced but typically do not wear out. They are not O-rings and will always feel hard, not soft. New pistons come with new Teflons but only the K1/K2 pistons are available new from MB.

I expect to be going down this road in the near future. Stay tuned...

 

[Otrebla49]

For best efficiency, view at 1.5x speed.

Here are the various videos in the series, so far:

Thanks so much Gerry!
These videos have helped me a lot at getting educated on how many things actually happen inside the 722.3 automatic gearbox from MB.
Alberto

 

[gsxr]

Found this excellent video on 722.3 teardown & rebuild, courtesy of @dionphaneuf.

See 20:30 for the K1 hidden O-ring, 27:10 for K2. Screenshot below of the K2 hidden O-ring dimensions. I assume 98mm OD and 2mm cross-section.

 

[gerryvz]

SuperKent has issued a couple more transmission-related videos, which I'm posting here so that the entire collection is captured. I believe there are quite a few more videos to come.....

How to fix shift problems

722.3 vs. 722.4 -- Differences

Comparing the old 722.1 to a 722.3

 

[gerryvz]

More videos as part of Uncle Kent's transmission series:

Valve body

Transmission Overhaul Tools & Parts

722.4 Hidden K1 & K2 O-ring Replacement

 

[gerryvz]

Found this excellent video on 722.3 teardown & rebuild, courtesy of @dionphaneuf.

I believe the fellow behind "JM Restorations" in Estonia, the author of this video series, is a member of this forum, FYI.