I second sun valley. I have two rebuilt trannys in my cars. One is sun valley and the other is a no name shop in Pasadena CA. The difference in shift quality is night and day.

I’ve written about my experience with Sun Valley here. They basically are building you a custom trans with multiple upgrades inside. It is an upgrade not a rebuild.

I love my SD and the way it shifts. My 300D is soso and I attribute it to the no name rebuild which incidentally cost the PO $1000 more than a SV trans. If you like the car and plan on keeping it, go sun valley. For you, you just buy, load (or have somebody load it) and then ship back the core. It’s worth the runaround.

I don’t know a lot about the 722.6. Have considered pulling the conductor plate and valve body and giving it a cleaning? Aren’t there some tiny screens in the solenoids that get clogged in those? Losing 1st and 4th sounds like a controls problem.(I reread your post and the slipping may be just dead plates and bands so I dunno).

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79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles

Sun Valley quotes $2,500 for the 722.6

Thanks for the feedback on SV! I do not know enough about those transmissions to make a half-way educated comment. I wish I could take the time to get into it but my young business takes up all my time.

I will drop off the car at a shop this week and take it from there. Once I have a better idea what the problem is I'll know what to do next. I do want to keep this car long-term so I won't cut corners. I have backup vehicles so I'm not under time constraints - other than wanting my favorite car back on the road.

Thanks again everybody for your input here!

Sun Valley may be able to custom build it for your application, give them all the details if you go that route.

Good luck!!!

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

On the older models loss of all forward gears is generally attributed a problem (broken?) B2 piston and or a broken B2 band.

The B2 piston can be accessed from outside of the transmission by removing the cover. If the B2 piston is in good condition you can get something and push on the B2 band to see if you can tell if it is broken.

I am not an expert on them but I believe your year and model should have the most updated B2 piston and the newer nylon bushing which is supposed to cure the piston breaking issue. However their is a lip seal there that can go bad.

On my 84 300D i had the slipping (flaring) issue and changing the filter and fluid cured that till about 1 year later the B2 piston broke.

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84 300D, 82 Volvo 244Gl Diesel

You sound much like me, regarding the newer models, though I have kept one om642 4x4 (in a Jeep) around for the deep snow times. That is an excellent example you have, in my opinion W126 were the last of the simple but overbuilt in all regards from DB in the S. klasse line. Everything is serviceable, and most systems remained independent, unlike w140 introduction to canbus and modular assembly. I've chosen the same car even after having some time with a w222 om642, at least until there are more full electric options with a bit better battery tech available. I may be a bit biased since I've been in a W126 since 1999 however.


Hopefully it is just a case of failed valvebody/solenoid, but just in case you decide to go the route of AMG box...



Here is a list of the PHX used inventory of pulled AMG boxes for the .636 from car-part.com:



I'm running that transmission in my 606 126 and it has taken some substantial abuse without complaint so far, the car I pulled it from was likely much higher mileage than those listed.

Pretty much any of the early 00s AMG v8s 722.6 can be converted easily. The V12s on the other hand, have a longer case dimension which may necessitate a new driveshaft and are a bit overkill, especially for near stock 606 HP/TQ outputs.

Belhousing swap instructions, though doubt a shop would need this:

https://ofgear.dk/generalinfo/bellhousing.html

In addition to that the output flange will likely need to be swapped from the 4 finger to the three finger, which also should be no big deal at any decent MB shop.

Thank you! I just started the car to see if I can move it into a better position for loading it onto my trailer. Reverse gear worked fine. It slipped into first gear and gained traction after some hesitation. It shifted up too. Then it started shifting up and down without me changing input to the accelerator. I turned around and then put it into reverse - nothing. I put it into D and back to R a couple of times and then reverse engaged again.

Given that I'm pretty clueless about this transmission I'm just making a guess here - to me it seems that there may be a controller issue. Or perhaps there is a bunch of dirt clogging things up. Or does this indicate physical damage? Maybe all of the above.

The OF controller did not show any codes so I'm not sure what is going on with it. It is possible that the controller doesn't like the heat in Arizona but I could get into the menus and it all appeared to work.

The shop still hasn't called me back after I've called them 3 times now so I have no appointment to get this looked at. Frustrating.

Just my opinion, in the past when shops didn't call me back, I simply showed up at their front door to talk with them. of course don't schedule your car to be delivered to them until you set an appointment......

That sounds like a pressure issue, like low fluid or clogged filter... unless the pump is dying or some kind of internal pressure loss. Do you have a dipstick tool for the 722.6 to check the level? How does the fluid look/smell? If you aren't familiar, there are charts that correlate fluid level to temperature which you can read with the internal sensor on the controller screen in D or R. More reading here: https://www.benzworld.org/threads/mercedes-benz-722-6-transmission-faq.1463460/#post-3647178 These are pretty sensitive to correct fluid level. If you suspect controller, you can remove power to the controller and put the trans in D, which will default to 2nd and R to see if engagement is different.

Yes, I agree. Unfortunately it's a 70 mile drive to that shop.

Thank you! That's great information! The car does have a tube and I assume it is attached to the transmission but there is only a plug in it - no measuring rod. Is there a special tool available? Thanks for all your help!

If you search for a 722.6 or NAG1 dipstick should come up from various suppliers, may even be available from Pelican. Don't use a random piece of wire as some have stated in that other forum post I listed, the tool doesn't actually go to the bottom of the pan but has a specifically sized tip that stops above the pan for correct measurement. If you use a piece of wire and go to the bottom of the pan you'll set it too low.

Thank you, I ordered one!

I have tried numerous times to call Sun Valley Transmissions and sent emails but no response. At this point I assume they're no longer in business. My car is still not fixed as I simply don't have much free time so it ends up on the backburner all the time. I do want my car back on the road though so I wonder if there are any other good sources for rebuild 722.6 transmissions. I'd appreciate any information you may have, thanks!

It will be costly but I'd look and see if a MB dealer rebuilt unit is available.

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Jim