info on 722.3 - 722.5 transmissions

[rschleicher]

During my digging into my own W126 transmission problem (no reverse gear engagement - since solved via B3 reverse clutch repair), I Googled the keywords 722.3, Mercedes, transmission, and repair, and found the following .pdf file:

http://w126.pp.ru/akp722.pdf

The web site it is on is some form of Russian W126 site (with cyrillic text), but the document itself is in English. It covers the transmissions used in 1995 and 1996 models, but several models of these years use 722.3xx transmissions, and so the info on diagnosis is reasonably valid for W126 models. The document covers 722.3 - 733.5 transmissions. I wouldn't want to use these for actual repair procedures, unless you had exactly the same transmission, but it certainly can help to understand the possible causes of most symptoms.

I have no idea if the web site that this is from had permission to post this document - it just came up via Google.

Bob Schleicher
1991 420SEL - 171,000 miles.

[rupert e]

I just want to say thanks for the post that you discovered for the 722 trans it was a big help!!!!!

[hurst01]

rschleicher,

Great link, it will surely be helpful. I have a 93 Mercedes 300 SL that has no reverse. Just went suddenly with no warning. It seems to work great otherwise. I haven't taken the time to read all of the link (59 pages), I am assuming that you had to disassemble the transmission somewhat to do the repair on B3 and that it is not accessible from the outside of the case??
Just wanting to determine what I am in for. I have rebuilt several GM transmissions but never a Mercedes.
Thanks, Ed

[rschleicher]

hurst01,

It's been 2 1/2 years since my post, so I have forgotten some of the details, but yes, repair of the B3 reverse clutch requires removal of the transmission and opening it up. I didn't do the work myself, I just had a local transmission shop do it. My main reason for trying to understand what was wrong was to make sure that I wasn't going to be lured into getting more work done than was needed.

In my case, I had lots of warning of the emerging problem, as I was seeing the typical symptom of reverse gear taking longer and longer to engage (seconds, then many seconds). Then it got to the point where it wouldn't engage at all without blipping the gas a bit (and then it would engage with a lurch). Then, shortly thereafter, it began not engaging at all. The older 722 transmissions (i.e., 722.1, 722.2) had an external reverse band adjustment. But the 722.3 and on require opening up the transmission to repair/replace the B3 reverse clutch.

The question that you have to think about is whether it makes sense to do a full rebuild while the transmission is removed and open. In my case, the mechanic said that everything else looked to be in pretty good shape, so I limited the work to just the B3 clutch, plus general replacement of seals. I am forgetting the price I paid, but it was a bit more than half of what it would have been to get a full rebuild.

Evidently I made an OK choice. I still have the car, which now has 192,000 miles (a bit more than 20k miles since the repair), with everything working fine. Good luck!

[stevebfl]

Sorta like russian roulette. The job to redo the B3 clutch pack is about 2/3 the whole job to rebuild. The failure always leaves a mess of trash in the tranny. We used to do a few localized repairs back when these trannies had less than a hundred thousand miles.

By the numbers one is a statistical extreme risk taker to not make the whole repair. For the few that have a working trans after surgery the risk is reduced. The real risk is issues from debris that can't be cleaned without total disassembly. Besides the same issues that cause the failure exist in numerous other areas. Unless you are just patching it for a resale dump on someone, you are the one that gets short changed by such short sighted economics.

The point is, whether it is worth it to spend 66% of the price of a complete repair to be driving around with a high mileage used tranny with trash in it. I'd rather just do a used tranny if that were the choice.

[gsxr]

Here's a factory document on 722.3 tranny repair... best one I've seen. It's a 7MB download (PDF file).

http://www.w124performance.com/docs/mb/other/tranny_722_repair.pdf

[emerydc8]

Anyone else having trouble opening this link? All I get is a white screen and a little X in the upper left corner.

[gsxr]

Try right-clicking the link and selecting "Save As", then save it to your hard drive. You'll need Acrobat Reader to view the file.

[emerydc8]

This is great information. Thanks!

[S-Class Guru]

This file is AWESOME. thank you, thank you, thank you.
I downloaded the Russian file mentioned above, then I paid $25 to download the ATSG document.

This one blows them both away. The diagrams are beautiful and the text makes sense. I'll let you know how good it really is next week, as I am dropping my tranny as we speak for a B3 clutch look-see.

DG

[emerydc8]

Take pictures, if you can. Good luck.

[the tenor man]

Hello all,

I have a 1987 300D Turbo that today just started to flare a tiny bit on the upshift...I thought it may be just the cold weather...about 15° F.

I checked the fluid and it looks fine but was down about 1/4 inch on the stick from the low mark...I added a bit but will need to recheck it.

Last summer I replaced the vacuum pump with a new later version...should I readjust the vacuum?...if so, how.

Should I first check the cable from the transmsiion to the throttle control?

Thanks in advance for any help.

The Tenor Man

[gsxr]

If the fluid level is really low, that could cause a slight flare. Make sure you check the level with the tranny hot, otherwise 5-10mm below the normal level is ok.

New vacuum pump should not make any difference. The cable to the tranny only controls the speed/RPM of the shift point, not the firmness.

When was the last time you changed the fluid & filter, and did you also drain the torque converter? This should be done at least every 30kmi, if not sooner. Using synthetic fluid is even better.

[crhenkel]

Just used the two manuals to guide me through a rebuild of my valve body in my 722.4 tranny, worked great and now the shifts are nice and firm and crisp. I put new piston seals and a spring kit from Superior in the valve body and it fixed the flares and the shifts. I hate those little steel balls but the manual helped me get them all back in the correct locations. Best $100 I have ever spent on my MB!

[a moussa]

95 s 500 coupe

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i need help please here is the problems
1-transmission goes only in reverse
2-as you move the shifter there is a rubbing noise as metal to metal rubbing
3-smokes a little with a bad smell from exhaust
4-humming or harsh sound in all shift positions except reverse it gets quitter in reverse