Hi all,

Been a long time since I've posted here, but my trusty W123 is in need of a hand.

A few months ago I was out running errands in the 300. Everything was fine, was running and driving great. Went in to a Home Depot and when I came out, the transmission would not engage any gear. No forward gears, no reverse. Neutral and park seem fine. The trans gave me no prior indication that anything was wrong. It was rebuilt about 7 years ago.

First thing I did was check fluid. It was low, so I added fluid up to the proper level. No dice.

I checked the linkage between the shift lever and the trans on the driver's side under the car, and as far as I can tell, it's attached. This was later confirmed by having my Ms shift the lever in the garage while I watched the linkage from below.

At the advice of Jono from Blue Ridge, I hooked up a set of trans gauges to the working pressure port on the trans. The needle bounced like crazy but showed roughly 200PSI in park, and a steady 60PSI with the lever in D.

I was referred to a well regarded old-Benz tech nearby who was known for transmission expertise. Unfortunately, there didn't seem to be any real diagnostic done by them other than "yeah, it doesn't work right. Needs a rebuild dropped in, $5,500." Disappointing for a few reasons, but I had her brought back home.

I have not dropped the pan yet but imagine that's my next step. Is there a possibility that the B2 piston (I see it mentioned a lot) would be a culprit given the behavior I'm seeing? What else should I be learning about to hopefully remedy this? I'm not opposed to putting another trans in, but that it just all of a sudden with no warning stopped working makes me think it's likely something simple that just gave out. Any suggestions are welcome.

Thanks!

I know you've said you've checked the gears, but be sure to check reverse. If you've got reverse but nothing else then its a B2 piston issue.

I'd be surprised if there wasn't a clunk/snap/pop but it could be a torque converter failure.


It sounds like its not a pump issue. The readings you give seem to line up with this test document.
Mercedes_722.3_722.4.pdf

Here's a great resource regardless.
https://www.w124performance.com/docs/mb/other/tranny_722_repair.pdf

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I recondition w123/w126/w124/w140/r107/r129/ steering boxes!


1984 300D "Elsa" odo reset 6/2011 147k
1983 300TD "Mitzi" ~268k OM603 powered
1995 E300 "Adelheid" 262k [Sold]

I had a transmission pump fail on my car a few years back. Same as you: no issues or warning, just suddenly didn't have any gears at all including reverse.

The main difference, however, is that my line pressure was quite low, and when i bumped the throttle it didn't really raise at all. Put in a Sun Valley rebuilt transmission, and all is well.

Your case is curious though. You aren't getting gear engagement, but you do have pressure. As someone already said, B2 brake comes to mind if you still have reverse.
As you said, it may be time to drop the pan and look at your valve body.

Also, attached is a diagram that may help you think this over.

Attached Thumbnails

 

No reverse at all, unfortunately. I'll report back here if there's anything worthwhile in the pan. Thanks for posting those links!

IIRC, this unit in the car now is actually a Sun Valley unit as well. Maybe 10-15k on it since it would have been installed. I'm sure it's well out of any warranty there would have been. Darn.

Unfortunately, the cost of a rebuilt unit (at this time, at least) just isn't something I can justify for this car.

About 5 years ago I also lost all my gears.
Got a valve body out of the junk yard from same model transmission,
swapped it in, and all was well. It's been working fine ever since.


Jeff

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1984 300SD 300,000 miles--two tank WVO setup
2.88 diff & 500SEL anti-squat rear end

Sun Valley is really good to work with, they would probably help with diagnostics.

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