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722.6 transmission problems!

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The 722.6 has been a very reliable electronic transmission and is much more simple to repair than its predecessors. One problem that was ongoing with this transmission are leaks at the plug adapter for harness connector. There are various versions of this adapter and o-rings, some have tabs, the adapter is best replaced complete with o-rings. If the adapter o-rings should be black, red or white o-rings are prone to leak, connectors with tabs will also leak. The electronic transmissions are lifetime fill in most cases and have a lock on the dipstick. If you replace the adapter you need to adjust the fluid level, the transmission dipstick is a special tool. The fluid used is not Dexron III but a variant of it, don’t use ordinary A/T fluid in an electronic transmission with lifetime fill. The correct fluid is 001 989 21 03, MB 236.10. This fluid is backward compatible with all earlier transmissions. The dipstick is a special tool and the dipstick cap has an anti-tamper plastic lock. The fluid after MY 2006 is the same in a 722.6 as a 722.9, don’t use the 722.6 fluid in a 2006. The newer fluid is slightly purple in color. The newest fluid is backward compatible with all Mercedes transmissions. Some late model 722.6 transmissions have a scheduled transmission service, oil and filter, at 39k. For all others even if its not required a transmission service if done with the correct fluid could only be beneficial, even if it isn't called for.

Early 722.6 transmissions had a poor valve body conductor plate design, this part has the starter lock out switch and transmission VSS sensors built into it and powers the shift solenoids. If it fails you may have an intermittent no-crank no-start condition and the transmission may shift irregularly because the speed sensor signals needed for calculate smooth shift adaptations are faulty. This part can be replaced with the transmission in the vehicle and the valve body removed, this is good to do if considering a transmission service on an older vehicle. If you are experiencing shifting concerns or start delay, please contact us for details as we can scan for codes that would indicate you need this repair or other transmission repairs.

One note on torque converters and transmissions, there is considerable variation in these parts and the best repair is installing and Mercedes-Benz remanufactured unit as it will be an exact match. Used parts will in most cases not match and may be problematic even if they are good, control units can be very specific and may not work correctly. Dealer remanufactured is the highest cost option but is the best and fastest turn around. Alternately, we can rebuild your transmission, and have your existing torque converter rebuilt depending on the extent of the damage. A torque converter may be rebuilt. They are sent out for this repair. They are punch marked, cut in half by a dedicated machine and cleaned of any debris. Inspected and the lockup clutches replaced if needed and welded back together on a dedicated machine. We don't recommend replacing one with an aftermarket remanufactured one, you are best to have the one from the vehicle rebuilt. There are too many variations of these to expect you will get the correct one, although it will fit, internally it will have a different design and stall characteristics. A new unit from Mercedes is the best repair but it may be over 3x the price of having yours rebuilt. In many cases the torque converter is replaced simply because it may be contaminated with material from the failed transmission and if it is reused the new transmission may be damaged, having it opened inspected and rebuilt eliminates this concern.

Another issue with the 722.6 involves transmission fluid wicking up the harness into the control module and causing the module to malfunction. Usually, the harness from the transmission to the ETC module is replaced and the module is replaced provided the leak is repaired. In some cases this may be more than is actually needed but it usually fixes the concern. Transmission fluid does not actually damage the module and can be flushed away with board cleaning solvent or electrical contact cleaner as a first attempt. Always repair the leak before replacing a module.

Another issue with the 722.6 was in Valeo radiators leaking coolant into the transmission fluid, this causes and harsh engagement followed by a droning vibration. There is a glycol test to determine if this is the case. If strongly positive the radiator, torque converter are replaced and the transmission and lines flushed. The dealer used to replace the transmission also but no longer does this commonly. If the contamination is slight the radiator only is replaced and the lines and transmission flushed. Consider having the transmission clutches replaced if the contamination is high, i.e. visible contamination. The clutches are very sensitive and it may not be fully repaired unless the radiator, torque converter and transmission are replaced or rebuilt. If you have this complaint and the glycol contamination is not present you may need a new transmission control unit, the newest software can correct an adaptation issue with the torque converter than can also be the cause. This should be diagnosed by a specialist. The transmission control unit is replaced and adapted to repair this because the transmission software is not flash updatable as it is on the predecessor.
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· Registered
1997 S420
136 Posts
Interesting information, I have been told that the early 5 speed transmissions suffered from early failure of thrust bearing / bearings and that parts from the failed bearing can find their way into the planetary gears creating extensive damage, is this likely and have you experienced such failures. If this is a likely problem what symptoms of pending bearing failure would you expect / experience.

· Registered
1997 E320, 1997 S320
2,951 Posts
one more thing to mention on 722.6 is the solenoid pressure regulator valve spring, which a little spring located on the side of the valve body that breakes. symptoms of broken spring are gear 2-3 and 3-4 slipping. the spring costs less than $5 and is very easy to replace. it affects only 722.6 up to 1999, which would include all w140 with 722.6. so if you are about to change the tranny fluid, might as well replace the little spring also.

· Registered
1996 S500 coupe
810 Posts
one more thing to mention on 722.6 is the solenoid pressure regulator valve spring, which a little spring located on the side of the valve body that breakes. symptoms of broken spring are gear 2-3 and 3-4 slipping. the spring costs less than $5 and is very easy to replace. it affects only 722.6 up to 1999, which would include all w140 with 722.6. so if you are about to change the tranny fluid, might as well replace the little spring also.
do you happen to have a part # as well as where exactly this is located?

· Registered
Merecedes E320 -2001 Model-75k miles as of 09/08/2010
26 Posts
Is transmission repair a good idea? URGENT ADVISE NEEDED PLZ!

I came across this thread and wanted to seeking your advise on a pressing issue that I have.

My car: Merc E-320 2001 model with 75K miles; have taken good care till now.

First time in the morning I always start the car and wait 45-60 secs before I move to let the fluids circulate.

My Issues:

Fundamental questions - a) Does it seem that I have a transmission problem?
b) Is it advisable to get a second opinion?
c) Is it advisable to go ahead with tearing the transmission up (without being 100% sure of a problem) and replacing any defective parts? If that is done by a reputed dealer, can I hope to get the transmission back in shape just the way the factory ones are?


In the morning when I leave my home I go about 200 yrds, and make a turn and another 500 yards and make another turn and try to go about 25-30 mph. Typically at the second turn when I press on the gas pedal I notice a slight slip in the transmission, which mostly does not happen again all through the day. I disregarded it thinking it may have been due to the engine being cold. I guess a similar slip has occurred may be just about 2 times over the past few months later during the day when the engine and fluids were already hot.

I have a comprehensive warranty on the car which is expiring in a month. I have used this warranty for 6 yrs. and they are pretty reasonable and easy to work with.

I also have a very slight oil leak (about a little bigger than a quarter size stain each day on the garage floor), very insignificant to make an impact on the engine oil level.

I took the car to one of Atlanta's leading Mercedes dealers to check on the oil leak, and also reported the transmission issue with only a VERY SLIGHT DOUBT that it was an issue.

On the engine oil leak they said the engine was leaking oil from the valves etc. and needed to fix those and the warranty covered most of it for which I agreed.

On the transmission they said there were no codes, but they said that they found some slippage in the trans., and say that even though the problem seems to have just started it will eventually surely fail. They dropped the trans. pan to see if there were any metal pieces there and did not find any. They said if that if they did find some metal pcs. they would have had no further tests and would have recommended a new trans. right away.

Now they say the the only way they can identify the problem would be by stripping the entire transmission and see what's going on, as the warranty co. wants a list of items that has failed. I spoke with their head mechanic and he said he SUSPECTS (NOT sure though) the "One way Roller Clutch" MAY have worn out and may need replacement, and potentially other parts too.

We (the dealership and myself) spoke with the warranty co. together, and they said they would NOT authorize complete replacement of the trans. with a factory reconditioned transmission, without first identifying the failed parts, and knowing the costs for their replacement.

My concerns:
a) I also spoke with another Merc mechanic and he said that the dealership should be able to convince the warranty co. for a total trans. replacement (if there was an issue) and he says it is not advisable to replace individual parts as it may result in trans. failing altogether within a few months. And, I am not comfortable disassembling my original transmission and letting these guys replace parts. I am not sure if they can set it up once again to factory stds., and also whether the old and new parts will work together cohesively.

b) This other mechanic said it's very unlikely that the trans, has really gone bad at 75K miles and most likely the problem would be with the "Electrical Plug" which may be leaking resulting in MINOR loss of trans fluid. I had myself checked the fluid level and it was fine. The dealership also said there was no leak at the plug.

c) The warranty co. is urging me to let the dealership proceed with the diagnostics to identify the problem, and they say if I refuse that and if the trans. fails later they will not cover it.

d) The dealership wants me to authorize of diagnostics at a cost of $1,200 (initially), and assure me that they will be able to find some defective parts inside and make the warranty co. pay the $1,200 cost

I am in a dilemna - my question is should I just ask them to service the trans. and do nothing more, or let them go ahead with the tear down of the trans. and may be replace necessary parts. I am not sure if the dealership is wanting to go ahead with the diagnostics genuinely to locate the problem, or to make max. money from the labor which can be as high as 20 [email protected] about $110 per hr.

I need to give them a firm decision tomorrow morning.

Thanks in advance for your help.

· Registered
nothing broken. finally!
2,619 Posts
a. dealership doesnt care who pays. they will replace the trans with a reman box from zf. if your ins doesnt pay they will just bill you. nothing you can do about it, they are under no obligation to deal with 3rd parties. keep that in mind and do not trust anything they tell you at the time. everything changes when you get handed THE BILL.

b. does he work at aamco? probably he does. 75k is a nice failure point for 722 of any version. loss of fluid is again, dubious topic with these. unless you can see it pouring out, you aint losing any. check for leaks inside the TCU. just for kicks, it might be seeping up there and messing with the controller.

c. thats between you and your wallet

d. doesn't sound right. seems like they are just playing you. 11 hour diagnostic..... what? 800-1200$ is the usual charge to change the conductor plate (ripoff price but whatever). that's what they will probably do. but to what purpose?

Like i said reputable mb dealerships no longer rebuild these. they replace them. not sure why said dealer will be wanting to go on an exploratory trip inside your box. probably just for $$$$. it's either broken or not. if you can't tell, keep driving. eventually it will show in definity.

id keep driving it personally.when it breaks then you deal with it. right now it just sounds like a whole load of nothing

· Registered
24 Posts
im working on a 01 C320 that has no engagment in ANY gear.and i feel what almost feels like a broken torque Converter.Heavy rumbling of a spinning mass that i can tell theres alot of weight to it..ive been working on MB's for 40 yrs and ive never seen a TC fail to spin the output other words drive the car.. this just doesnt feel like the trans itself .. i found zero debris in the pan and my scanner is showing no TC rpm but i havent repklaced the contact plate (above the Vbody) yet cuz i didnt wanna waste the money if it didnt fix it even tho when i worked at the dealer thats what i would have done cuz sometimes its quicker to throw parts at irt instead of whipping out the multmeter to do pin tests..what im asking is if the ETC module is completely unplugged shouldnt the trans at least engage SOMETHING? .. have u ever seen a TC fail like im thinking it almost have to happen in this case... car has 140k miles
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