Mercedes 722.9 (7G) Owners Information
JT Automatics have become inundated with Mercedes 722.9 (7G) automatics that share similar problems.
These problems are normally shift feel problems like a bumpy 3-2 down shift or a 3-2 upshift on light throttle, quite often these vehicles have either been purchased with these problems, or have had work like electronic /mechatronic replacement, Mercedes run many different shift control programs that are matched not only to the vehicle chassis number but also to the valve body type and torque convertor (2 or 3 plate lockup)
The problem begins when the wrong software for the wrong valve body is loaded, while it is correct for the chassis number it’s is often the case someone has changed the valve body for the wrong type these are also fitted incorrectly from the factory however a special software programme is used, when this happens it’s often programmed with the correct chassis number but wrong valve body, when the electronic plates (tcu) are changed the software is changed for the valve body that should be in the vehicle and harsh shifts are produced.
Well that seems straight forward……… well not quite? another reason for these shifts are solenoid mixing the solenoids energize at different current ratings and cannot be mixed up, there are eight solenoids 1 set are normally open, there are 4 of these( interchangeable ) and one set of normally closed solenoids, again there are 4 of these also interchangeable, its very easy to get these mixed up when changing the electric plate and unfortunately this happens at an alarming rate at both rebuilders and main dealer alike, the vehicles Tcu will be able to adapt some of the shifts while not being able to adapt others , working out exactly what solenoids are mixed makes this process time consuming and very difficult to rectify, main dealers often shrug off the problem with suggestions that the vehicle needs a new gearbox , while transmission companies are often disbelieving that the customer did not have these complaints before the work was carried out.
The next issue is the torque convertor, we have some very good torque convertor builders in the Uk but that doesn’t take away the fact some of the Mercedes torque convertors are suceptible to slight parameter changes of a rebuild, given the fact that torque reduction is carried out through out the convertor lockup range, it’s important that the convertor is preforming at its peak, anything less causes premature torque convertor failure poor fuel economy and sharp shifts if the lockup curve is incorrect it will never perform properly , this is also controlled by one of our solenoids and differing sized lockup valves and springs dependant on valve body type which is in turn is controlled by the Tcu software, to our knowledge Mercedes use 5 standard lock up curves as well as various bespoke lockup curves.
So where do we start?
First, we would need to check your adaption data this will confirm that we have no internal problems before we start chasing the problem
Your adaptions will look a little like this:
This will provide us with all the information as to what’s going on in your transmission. Wear. oil pressures, torque convertor information, this we can read from the Tcu in the car or on the bench from this information we can make the decision as to remove the gearbox or to check the coding and valve body information as seen here
This now tells us what valve body the vehicle is programmed to what programme was used and if the car specific coding is correct this can all be cross referenced to huge data base using Mercedes own tools and more importantly an incredible data base gathered and gifted to us by our European partners, if all this checks out we can then investigate the shift and torque convertor curves using a recalibration tool,
We have pre-set curves we can use to recalibrate the shift pressures, if the wrong solenoids have been placed in the wrong positions we start with saving the original data to which we can always return to the vehicle should it be needed, this process does take time but it not only means we can correct problems introduced but also overcome fitting new parts with old without any conflicts, this also eliminates having to occasionally purchase new convertors when the slight parameter changes in rebuild process can now be recalibrated
We have included two different curves both are correct, but it demonstrates the difference in shift and convertor curves between similar cars with different valve body’s
As a complete service we rebuild our own Tcu’s and re-code them, there are some bespoke codings which also means we can keep these and replace them on to the new Tcu, we also save all the original setting of customers Tcu’s, although we have never been asked to replace our calibrations with original these are always held on file to help us build a better data base, this also means for the customer we can be more than competitive with price now as we don’t have to purchase new valve body’s or torque convertors, we can can now use recondiitioned convertors and have stock of all valvebody variations, all our coding is done in house and not remotely like our competitors, so we can guarantee that all the parts are matched with software before it’s reinstalled, your vehicle will be matched the very same as it was when it left the factory and thus returning the pleasure that driving a Mercedes once was
So why not phone us to see how competitive we can be!
How can we help you?
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