Gabriel444

Hello everyone. New to the board. Our car is a 2004 CLK320 Convertible. I've been going through the forums and I think I might have an idea of what the issue is, but thought it would be good for other opinions.

The car just started a few days ago to shift hard in lower rpm shifts, both sport and comfort mode do this. Then when I came to a stop on several occasions I heard like a vibrating or rumbling noise from the transmission or maybe engine area.

First thing I did was order a dipstick to check transmission fluid level. It was about 1qt low and sitting on the low side of the cold mark of the stick when at about 100c on engine temp. Added 1 qt of approved synthetic fluid and now it's fine, at upper part of 80c on stick, but not over filled.

That did not fix it. So on looking through the forums I found issues with the Transmission Solenoid Valve that controls RPM shift points?

I think it definitely has something to do with the transmission not shifting correctly with right gear at normal accelerations, and it only seems to do this jerking between 1st, 2nd, and 3rd. At least it feels like a little after it shifts it surges again. NOW -- when I smash the gas in both comfort or sport modes it shifts perfectly all the way up to max 6,000 rpm. BUT -- like I said, slow take offs it seems a little jerky in between or right after the gear shifting through the first 3 or maybe 2 gears (not sure yet).

EXAMPLE: I can drive slow (20 mph) up a steep hill in the neighborhood and it starts to make that vibrate noise again. I look at the tach and the RPM's are chugging at around 1,100 and I notice the motor is pulling hard. I manually shift down to 2nd and that works, seems it was trying to take the hill in 3rd gear. As strange as it seems I think when I do hear on occasion when I stop the rumbling sound, I think it's the transmission not downshifting or "maybe" the torque converter not getting the right signal from the electronics? I don't know.

I say that, because, when I manually pull the gears down as I slow down to a stop, there are no problems.

I've also noticed since that driving in town it is in "drive", last gear, at around 35mph.

I've reset the TCU several times and that has not adjusted the transmission to fix that to my driving style. I find myself if needing it, to manually shift down to 4th gear at 35mph to 40mph range. I think it runs better in 4th than in D at that speed.

Sorry if this is too long, but don't know how else to give all that I've seen happening with it.

Is there a diagnostic tool I can buy to inform me of transmission problems or should I go to a shop that can tell me if a solenoid valve or any electronic part is malfunctioning in the transmission?

Hope I gave enough info. Really enjoy the Mercedes -- great cars! I've also read the 722.6 transmission is a real good one and easier to repair if needed.

Gabriel

xsever

First thing I would do is get under the car and inspect the pilot bushing if it's leaking fluid into the wiring. If it is, then that fluid would have made it up all the way to the TCU which is housed in the footwell of the passenger side. It's a known problem with these cars with the old pilot bushing design. When fluid gets into the TCU, all sort of things start to happen.

Research the forum about this to learn more about what needs to be done and carry out the check before throwing money at a scanner and/or parts.

Rudeney

Welcome to the forum! Please visit the User Control Panel and add your location (at least country) to your profile.

The Autel MD802 Maxdiag Elite is reported to be a good one if you don't want invest in an SDS clone.

Gabriel444

Thank you for that suggestion. I will look into the bushing. And is there a way to clean the TCU if fluid is built up in it? Instead of replacing the TCU? I'll have to locate it.

Gabriel

Rudeney

The TCU is located in the front passenger footwell. Pull the carpet down from under the dash, and you will find a foam insulation panel. Remove that and you'll see a metal "cage" held in place by some plastic nuts. The ECU is attached to the inside of that cage. If you see oil on the wiring, remove the TCU, open its casing and clean it and the wiring thoroughly. Also, replace the pilot bushing seal on the connector at the transmission and clean those wires. If there's no fluid intrusion in the wiring or TCU, then I would still get a good scan tool and codes.

Gabriel444

Thank you Rudeney. If I understand correctly concerning the pilot bushing -- is that if it is leaking then it gets ATF on the connection at that point causing problems with shifting?

And potentially it could work its way up to the TCU via the wires?

I'm assuming if there is no ATF coming through the wiring at the TCU then the problem could be the connection at the pilot bushing?

Thanks again,
Gabriel

xsever

If the pilot bushing seal is leaking, ATF will make its way to the wires and all the way up inside the wires to the TCU which is in the passenger footwell. When that happens, and I've had it happen to me, the car will jerk its shifts and stop shifting at all. It will be stuck in a gear. Once the TCU was cleaned up and the new pilot bushing seal replaced, everything went back to normal.

Gabriel444

Sounds like an easy job to do with the TCU if needed. Is there any need to take it to a Mercedes shop to have the TCU turned back on?

I assume the procedure is to first disconnect the battery, then remove the TCU and open it to clean it.

I'm asking because I thought I saw in a thread on this forum mentioning a Mercedes shop needing to turn the TCU back on with a specific code?

Thank you -- this is really helping.
Gabriel

Gabriel444

I just looked at the TCU and I don't see or feel any fluid seeping through any of the wiring into it.

By the way is the TCU and TCM both the same? Are they referred to with different names sometimes? Want to make sure I looked at the right one.

Thanks,
Gabriel

Rudeney

TCU is and acronym for "Transmission Control Unit". TCM is an acronym for "Transmission Control Module". They are just different words for the same thing. On the 722.6, there is no coding needed for the TCU, although the shift points can be reprogrammed with SDS. If the wiring and TC are dry, then fluid intrusion is not the issue. In that case, I'd go back to my previous advice: Pull codes from the TCU.

bubsis40

Is SDS short for "Safety Data Sheet"? I'm interested in trying to reprogram the shift points with my car.

Thank you -

bubsis40

Please disregard...found it "Star Diagnosis System"

irokdastar

I had this issue . I removed the passenger side carpet and removed the ecu . I used electronic cleaner on the terminal of the ecu . Then i took break cleaner and sprayed the wire as far back as I can . you wont believe what came off . Put a towel under the wire so you don't make a mess . If that doesn't work you need to plug the car into a Icarsoft or Mercedes star and see if you have any codes on the transmission . Typically you wont get a check engine light . These transmissions are typically waterproof except for the bushing that everyone is telling you about and the conductor plate . After I got the ecu cleaned a few month later I had to replace the bushing and ultimately the conductor plate . If your in NY I have a star system I can check it for you .

bubsis40

Thanks irokdastar. My mechanic pulled no codes for the entire vehicle so it's a mystery what's wrong. I would have to take my car in to have them replace the bushing and conductor plate, if that's the issue. I'm thinking the cost to do those may approach the cost of a used trans.

I appreciate your advice.

echanlyn

I just had this same experience and had to get the wiring module replaced. After 17 years , I've got a 2003 CLK500, things just wear out, plus I had never had transmission fluid changed. Recommended is every 30k, so I purchased 10 yrs ago with 62k, and current mileage is 122k. Used Liquid Moly trans fluid.

Car kept jerking at low speed, went to two mechs, each provided the same diagnosis. Do I know for certain, ahh? I'm not a mechanic. However, after getting work done, car no longer jerks, and acceleration is more linear.

Cost from one shop $850, other was $200 more.

irokdastar

the conductor plate is about $250-$300 and you will need a new gasket and filter about $20 and 6 quarts of trans fluid . Its all done from the bottom of the car and does not require you to remove the transmission . Are you a good DIY? I did it with floor jacks about a 2 hour job .