W203 Tranmission replacement advice - Mercedes-Benz Forum
 
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post #1 of 10 (permalink) Old 04-25-2019, 12:38 PM Thread Starter
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W203 Tranmission replacement advice

I have a 2004 C320 4matic with about 190k. It had shifting problems, but no engine light or codes with a ODBII reader. I bought a new Foxwell scanner. No codes in the trans. The speed sensors both read what I would expect (in real time). So I drained the fluid and dropped the pan. Lots of shiny sparkly stuff. So it is dead.

I bought a used trans (same type, year, etc) from a mechanic who claimed it has 70k-80k, but a bad conductor plate. The old filter is not there (he cut it up to inspect, claimed no metal flakes), so this is a bit of a gamble.

I plan on opening the replacement trans to inspect, and replacing the following parts:
- Conductor plate and related (plug, oil, filter, etc)
- Front seal (oil pump seal)
- Overlap valves (if they look worn)

I will flush the "glitter" out of the trans cooler.

Questions:

Is there anything else that I should consider replacing while I have the chance?

There is a bellows at the back of the trans near the park pawl on some transmissions. I have read that this leaks. Mine is a 2004 722.6 4matic. Is this part only on earlier models or RWD?

Any advice on this would be helpful.
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post #2 of 10 (permalink) Old 04-28-2019, 09:47 PM
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Have you checked that the TCM in the passenger footwell is clean and dry? Open it up to be sure.

With 190K miles, MAVA (check the 210 forum) would suggest a new torque converter (~$200). These TCs have clutches that wear.

While you’re in there be ready to replace the engine rear crank seal. You’ll need the seal and the special MB sealant for the seal carrier.

Sixto
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post #3 of 10 (permalink) Old 04-29-2019, 05:06 AM Thread Starter
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The replacement "low mileage" trans came with it's torque converter, and I am planning on using it.

I had not thought about the rear main. I pulled the trans on Saturday and haven't been under there yet. After reading your suggestion, I looked at the rear main. It is leaking. Good call. I will replace the seal.


Thanks,

Steven
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post #4 of 10 (permalink) Old 04-29-2019, 06:17 AM
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It's unusual for a 722.6 to fail at that mileage. I wonder if your radiator let coolant get into the ATF. I like the safety of a completely segragated transmission cooler.

Since you're also doing the conductor plate I would also replace the TCC solenoid while you're in there. It's the first one to wear out and cause hard shifts.

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post #5 of 10 (permalink) Old 04-29-2019, 09:57 AM Thread Starter
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tjts1,


Quote:
It's unusual for a 722.6 to fail at that mileage. I wonder if your radiator let coolant get into the ATF. I like the safety of a completely segragated transmission cooler.
The failed trans had 190k, and metal flakes in the bottom of the pan.

There was no red tinge to the coolant, which is the test for coolant contamination given in the Star manual. I did not notice anything strange about the trans fluid when I drained it. (Other than the sparkles.) What should I look for in the fluid?



Quote:
Since you're also doing the conductor plate I would also replace the TCC solenoid while you're in there. It's the first one to wear out and cause hard shifts.
Are you talking about the TCC damper or the solenoid? I measured the resistance of all the solenoids and they are good.

Steven
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post #6 of 10 (permalink) Old 05-20-2019, 10:14 AM Thread Starter
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722.6 compatability

I am now looking for another transmission.

Can I use any 722.6 4-matic transmission in my 2004 C320?
Are there any compatibility issues for example, do I need to swap in the TCU from some models years?
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post #7 of 10 (permalink) Old 05-20-2019, 07:30 PM
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post #8 of 10 (permalink) Old 05-20-2019, 10:19 PM
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Originally Posted by Steven_Renich View Post
tjts1,


Quote:
It's unusual for a 722.6 to fail at that mileage. I wonder if your radiator let coolant get into the ATF. I like the safety of a completely segragated transmission cooler.
The failed trans had 190k, and metal flakes in the bottom of the pan.

There was no red tinge to the coolant, which is the test for coolant contamination given in the Star manual. I did not notice anything strange about the trans fluid when I drained it. (Other than the sparkles.) What should I look for in the fluid?



Quote:
Since you're also doing the conductor plate I would also replace the TCC solenoid while you're in there. It's the first one to wear out and cause hard shifts.
Are you talking about the TCC damper or the solenoid? I measured the resistance of all the solenoids and they are good.

Steven
Measuring the resistance of the solenoid valve won't tell you if the valve is mechanically worn out or damaged from millions of cycles.

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post #9 of 10 (permalink) Old 05-21-2019, 01:22 PM Thread Starter
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tjts1,

Quote:
Measuring the resistance of the solenoid valve won't tell you if the valve is mechanically worn out or damaged from millions of cycles.
What is a better way to test this? I have seen youtubers click them with 12V. Would it be obvious if the solenoid way bad or sticky? Also, I could connect up the scanner to see live data if the trans is in a car - would this be able to tell me about the TCC solenoid?
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post #10 of 10 (permalink) Old 05-21-2019, 02:32 PM
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Originally Posted by Steven_Renich View Post
tjts1,

Quote:
Measuring the resistance of the solenoid valve won't tell you if the valve is mechanically worn out or damaged from millions of cycles.
What is a better way to test this? I have seen youtubers click them with 12V. Would it be obvious if the solenoid way bad or sticky? Also, I could connect up the scanner to see live data if the trans is in a car - would this be able to tell me about the TCC solenoid?
It's a $28 part. The TCC solenoid is used twice in every single shift. It PWMs so it's done millions of on/off cycles. It wears out much faster than every other solenoid in the 722.6 Do you want to open up the transmission again when you get the 1-2 hard shift?

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