I recently decided to replace my 2004 SL600's 5-Speed (722.6 or NAG1) transmission's "Conductor Plate" as a preventative measure. I had ordered a quality kit from FCP Euro a while back and now was the time to open it. Besides a German made conductor plate, it included a new filter, pan gasket, housing for the electrical connector with o-ring and a cap for the trans fluid fill tube. I already had a 722.6 dip stick tool and 2 Gallons of Valvoline Maxlife Automatic Transmission Fluid which has the MB "236.8+" designations.

NOTE: Since this forum does not allowing making edits after 24 hours, check for later posts for any corrections and feedback.

Here is a picture of all the hand tools I used, a very modest number. (Yes, I used battery impact drivers, but unnecessary and have to be used with extreme care as torque values are very, very low.) Essential is a Torx 30 socket, a 5mm hex socket and 8mm and 13mm sockets. Optional are 8mm and T30 nut drivers, a 7mm deep socket and a mirror (to align the connector housing). Also nice is an E10 External Torx socket, although a 8mm socket will do in this case. You might need a 8mm box-end wrench, ideally racheting, to remove a heat shield. A 1/4" torque wrench is highly recommended to get the conductor plate bolts tightened to 8 Nm or 71 Inch pounds. (That is about as tight as an average man can twist with a nut driver. Note "Inch/Pounds, not Foot/Pounds). I use a cheap Harbor Freight 1/4" torque wrench which calibrated in Inch/Pounds.



Obviously, a hoist is preferred, but jack stands will suffice. I recommend starting with a cold trans to prevent burns. You can drain the trans into an oil catch bucket, but ideally have a catch as large as the trans, as it will drip fluid from everywhere when the pan is removed.

NOTE: If you have a way to determine how much trans fluid you loose during this job, you will then know exactly how much new fluid to replace when done. It is not trivial to get the level correct with this transmission.

Step 1. Remove the plastic cover under the transmission to fully access it. These are 8mm bolts.

Step 2. Determine what is in the way of the trans pan being removed by dropping it straight down. On my car I noticed a bracket (originally) supporting the front exhaust, a bracket to which the plastic cover bolts and some type of protection plate at the rear of the trans. Remove them all, likely with an E10 or 10mm socket.





Step 3. Drain the transmission. With luck you have a 5mm hex drain plug. If not, start loosening the T30 bolts holding the trans pan until fluid comes out.




Step 4. While the fluid is draining, remove the electrical connector to the transmission. If there is a heat shield, use a 8mm box-end wrench to remove it. The connector has a lever on the left side; pull it down counter-clockwise the connector will pop off.



Step 5. Fully remove the trans pan and its T30 bolts. Pull off the fluid filter. The internals will continue to drip like crazy. Inspect any magnet on the pan; remove and clean it. Hopefully it is just fine powder and no metal chunks. Clean the pan if you are like me.




Step 6. Remove the connector housing from the trans. It is held by a single 7mm bolt. A 7mm socket on a long extension is ideal for this. Unscrew it about 10 turns and then pull the housing out; you may need needle nose pliers or long screwdriver as its o-ring can be tight.





Step 7. Loosen the T30 bolts holding valve body in place. IIRC there are 4 in the back and 5 in the front. I say "loosen" and not yet remove because a lot of additional fluid will now come out and we don't want the valve body to slip out of your hands. (Like mine almost did.)




Step 8. Now hold the valve body in place with one hand, and remove all the bolts with the other. A T30 nut driver is handy here. Keep holding it up! Now lower it carefully while making sure it is not getting caught in the rear corner where the shift rod is. Lower all the way and it is out! Place it on your work bench.





Step 9. Pop the plastic covers off. (One is already off in the picture.) There are three sets of solenoids; remove the T30 bolt which holds in each set. The solenoids will be re-used. Remove them and do not mix them up. (Its not a big deal if you did mix them up because the different ones have different nozzle sizes, but save time and keep them straight.)






Step 10. Remove the conductor plate. I found it hung up a bit in the upper right corner of my picture, but it will come/snap off. In this picture I point to the "manual shift rod". It easily moves in and out and you will need it pushed fully in when you re-install the valve body.




Step 11. Snap in the new conductor plate.

Step 12. Reassembly is a straight forward reversing of steps 9 through 3 Above. Bolts are torqued to a very modest 8 Nm. Trickiest is making sure the "manual shift rod" engages the shifter Mechanism pin correctly as you lift the valve body into place. Assuming you left the shifter in Park, press the shift rod into the valve body as far it goes and it should be very close to the correct position. REMEMBER to install a new fluid filter; turn/position it as close to the valve body as possible. I noticed that the new pan gasket sits rather loose; it doesn't "snap" in or anything; therefore make sure the gasket stays positioned as you begin to tighten the pan bolts, again to just 8 Nm. If your pan has an drain plug, make sure to use a new sealing washer.





Step 13. If you were able to measure how much fluid came out, great; that tells you how much to put back in. Still best to always check it. If you have no idea how much came out, add 3-1/2 quarts as a good starting point. You likely need a small funnel to fit the small fill tube. And yeah, just pop the fill tube cover off.

Step 14. You will need a "722.6 dip stick" tool to check fluid level. They are about $10 on Amazon. Start engine, insert the dip stick as far as it goes and pull out. You may have to repeat a few times to get a clear reading. Since the fluid level changes rapidly with transmission temperature, note the temperature reading on the dipstick, typically between 20C and 80C. In other words, try to complete the filling while the trans is still near 20C.

Step 15. Assuming the rear wheels are still off the ground, hop into the car and check that the wheels move backward in Reverse and forward in Drive.

Step 16. Reverse steps 2 and 1 above to complete the re-assembly.

 

Nice job and thanks for taking the time to put together a DIY writeup.

 

Thank you for the kind words. There are YouTube videos on this repair, but they often seem to skip steps. Here is one: BTW - The 722.6 is also often called the "NAG1" transmission which was used in many Chrysler vehicles from 2005 to 2020 with rear wheel or all wheel drive, such as the 300, Charger, Cherokee and some RAM pickup trucks.
Technically, the NAG1 is the MB model "W5A580" with a conservative rating of 580 Nm or about 425 ft/lbs. Many non-AMG MB used the W5A580.
The SL55, SL600 and SL65 used the model W5A900" with a rating of 900 Nm or about 665 ft.lbs.

As a result, repair parts are readily available, some upgrade parts are available and most transmission shops should be able to rebuild or diagnose one.

 

Nice writeup.

I would have done mine myself when mine blew (7-speed tranny) but had no hoist back then so copped the dealer's $3500.00 fee (but included a complete transmission service and they replaced the valve body free - don't know why).

 

Very detailed thanks OP.

 

Hello! Did you experience any difficulty loosening these bolts? I stripped two and stopped...

 

Yikes. They should not be all that tight. The spec is to tightened to only 8NM (about 6 ft/lbs) which is about what someone with moderately strong wrists can reach with just a nut driver. I tightened to 8 ft/lbs because that is what other transmission I work on spec for the same M6 size bolts.
I suspect someone before you worked on it and greatly overtighten the bolts. I suspect they will break at around 20 ft/lbs.
What is you plan? The trans won't work well for long with two missing bolts. Was there any corrosion?
I suspect after your remove the valve body that any broken bolts will come out very easily with an extraction method such as a reverse direction drill bit.

 

Followed procedure for conductor plate replacement. Kit from fcp euro
shift gear in proper place after reinstall,
all codes cleared with obd scanner
refilled exact amount fluid
dropped oil pan to check filter and plastic shift mechanism location
found 1/4 inch fluid in pan
Reset car disconnecting batteries overnite. No luck 722.6 five speed 2003 SL500 149k
Any suggestions for next step would be greatly appreciated
Thank You

 

When you dropped the trans pan (the 2nd time), did you first drain the fluid?
If not and there was only 1/4" of fluid in the pan, then your fluid level was much too low.
IIRC, after dropping the pan on a 722.6 (and many other automatic transmissions), adding 4 quarts is a good starting point.
Remember that the fluid level on an automatic transmission has to be checked with the engine running because the trans pumps several quarts into the torque converter.

Sorry if I didn't notice your problems in another thread, but what is your problem and its symptoms?

 

thank you for your reply
when I initially drained the transmission and dropped the valve body
I collected all of the drained fluid
41/2 liters measured
I replaced that amount thru the transmission filler pipe at rear of engine
i did not drain torque converter
it’s almost like there is a plug in the tube Tran dipstick bottoms out with fluid 6 inches up from bottom
In the morning I’m going to disconnect tram hose to radiator at the housing
run engine until warm and see what happens
honestly seems like that would cause big leak
i will certainly let you know what I find
College football game tomorrow so may be Sunday before I can reply
thank you again for your reply
i have a 98 SL500 and it’s not close to my R230 love the ride

 

In case you see this before Sunday, please tell us what trans problem you are experiencing.

 

car missed a gear when I stepped on it to accelerate out of a curve on a bypass hill incline. It took a second to reingage and continued 100 mile trip
Drove car another 2/3 hundred miles
No issues. But I was aware and did not drive it hard til parts came in
Have never had any issue before
149 k miles
replacing conductor plate is a wear item at that milelage
looked like a 3 hour job. Next step was reinstalling original plate. Likely hood of bad part is miniscule. BUT
Again I appreciate your help
I’ve owned car for 15/16 years
Done most work on it myself
Replacing shocks rebuilding abc to include pump replacement and a/c compressor etc etc
Im 76 keeping it til my wife has to sell it
lol

 

That problem does sound like a conductor plate problem.
What is the problem now? Doesn't move forward or backward? If yes, that is usually very low on fluid, filter no installed correctly or filter clogged.

 

Yes no movement forward or backward
will check filter in the morning
again thank you !!

if filter is ok
im going to add fluid one liter at a time

 

If you are going to check the filter again, note how much fluid comes out. Do you have a drain plug on the trans? (Some do, some don't).
Bolt the oil pan back and add 4 quarts/litres of fluid and you should be good to go and later make a precise level measurement. (Don't test before adding the full 4 quarts/litres.)

BTW - I use Valvoline Maxlife trans fluid (Red Bottle). It has the specs recommended for this trans.

Maybe too basic for you, but a member here creates great YouTube videos on these cars. Here is the one on checking the trans fluid level: