W204 2012 C300 (3.5L) DIY ATF Change - a few learnings to share
02-03-2016, 05:52 AM
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W204 2012 C300 (3.5L) DIY ATF Change - a few learnings to share
Having just completed an ATF change on my 2012 C300 with the 7G-TRONIC PLUS transmission and 3.5L petrol engine (code 276957), I thought I would add a few small points to the knowledge register on this topic, building on the important contributions of Scott Elliot, Glyn Ruck, John Anderson and others.
In my opinion, the procedure has been beautifully described by these authors, so thanks to them, the exercise by and large went to plan, apart from 2 annoying issues.
Firstly, on my car, the Torque Converter ("TC") drain screw was a long way forward (towards the front of the car) of the access aperture. So instead of having a direct line of attack to the screw, the line of access was at about 45 degrees and the screw was about 15mm forward of the front edge of the access port. The only way I could loosen it (after trying everything else, very patiently, for a couple of hours) was to use a 4mm hex key, modified by cutting the short end down to a total length of 6mm and applying a 45 degree bend (outwards) about 15 - 20mm down the length of the long shaft. The access angle was otherwise too extreme for the ball end of a hex to work, let alone any socket, universal joint or extension setup that I had available - and I had quite a few. Also note that I could only remove the screw via a second rectangular aperture located at 4 o'clock on the transmission housing (looking towards the front of the car). This second aperture (also covered by a thin rubber plug) was in addition to the standard, circular, 6 o'clock aperture. I have not seen this second rectangular point at 4 o'clock described elsewhere.
Based on this experience, I would suggest that if you are contemplating an ATF change, you assess the access and appropriate tooling required to remove and replace the TC drain screw before you embark on the exercise.
The other trap that I fell into was trusting my (up to that point 100% trustworthy) click-type torque wrench to click at the required 4Nm while it was upside down, despite multiple successful prior tests in a horizontal plane. This occurred while I was attempting to torque up the 6 x one-use aluminium pan bolts - 2 broken bolts, a quick trip to my Mercedes dealer, and the use of good old fashion 'feel' later, I was in business.
I now know that this risk with a torque wrench is pretty common knowledge, particularly when using low torque settings, but I thought I'd just call it out again here. I'm currently looking into adding a deflecting beam torque wrench to the arsenal...
For those planning this service, a few other things worth noting (in no particular order) are;
1. My transmission took a net 8.8L - I filled it to 9L and drained out (at full flow) approximately 200ml before it started to slow.
2. Draining the torque converter is slow, and took me a full 20 minutes
3. Heating the transmission to 45 degrees C, took about 15 minutes (25 degrees C outside)
4. On my car there was nothing to remove at the front edge of the transmission pan (others have described electrical connectors or brackets) to allow the pan to be removed. I did however have a T30 screw to remove adjacent to front right (looking towards the front of the car) pan bolt.
5. I did the ATF change at 4 years / 32,000 kms, and would describe the old fluid as 'somewhat' discoloured and there was also some definite sediment sitting on both magnets.
6. Improved smoothness and responsiveness of the transmission after the service was noticeable to me. (Hopefully not placebo effect).
7. My crankshaft pulley nut took a 27mm socket, and with a long breaker bar, could be turned (clockwise from the front) from underneath the car (transmission in neutral and the car was on a hoist).
8. My car, having the later 7G-TRONIC PLUS, took MB 236.15 ATF.
9. I changed the diff oil at the same time (I'm a change all the fluids by 4 years guy). This was very straightforward. Bought a short 14mm Hex socket on-line to access the drain plug, and it took a full 1.2L of Fuchs Titan Sintopoid FE SAE 75W-85.
I trust these tidbits help encourage others to complete this very worthwhile maintenance and / or avoid some needless aggravation.
In my opinion, the procedure has been beautifully described by these authors, so thanks to them, the exercise by and large went to plan, apart from 2 annoying issues.
Firstly, on my car, the Torque Converter ("TC") drain screw was a long way forward (towards the front of the car) of the access aperture. So instead of having a direct line of attack to the screw, the line of access was at about 45 degrees and the screw was about 15mm forward of the front edge of the access port. The only way I could loosen it (after trying everything else, very patiently, for a couple of hours) was to use a 4mm hex key, modified by cutting the short end down to a total length of 6mm and applying a 45 degree bend (outwards) about 15 - 20mm down the length of the long shaft. The access angle was otherwise too extreme for the ball end of a hex to work, let alone any socket, universal joint or extension setup that I had available - and I had quite a few. Also note that I could only remove the screw via a second rectangular aperture located at 4 o'clock on the transmission housing (looking towards the front of the car). This second aperture (also covered by a thin rubber plug) was in addition to the standard, circular, 6 o'clock aperture. I have not seen this second rectangular point at 4 o'clock described elsewhere.
Based on this experience, I would suggest that if you are contemplating an ATF change, you assess the access and appropriate tooling required to remove and replace the TC drain screw before you embark on the exercise.
The other trap that I fell into was trusting my (up to that point 100% trustworthy) click-type torque wrench to click at the required 4Nm while it was upside down, despite multiple successful prior tests in a horizontal plane. This occurred while I was attempting to torque up the 6 x one-use aluminium pan bolts - 2 broken bolts, a quick trip to my Mercedes dealer, and the use of good old fashion 'feel' later, I was in business.
I now know that this risk with a torque wrench is pretty common knowledge, particularly when using low torque settings, but I thought I'd just call it out again here. I'm currently looking into adding a deflecting beam torque wrench to the arsenal...
For those planning this service, a few other things worth noting (in no particular order) are;
1. My transmission took a net 8.8L - I filled it to 9L and drained out (at full flow) approximately 200ml before it started to slow.
2. Draining the torque converter is slow, and took me a full 20 minutes
3. Heating the transmission to 45 degrees C, took about 15 minutes (25 degrees C outside)
4. On my car there was nothing to remove at the front edge of the transmission pan (others have described electrical connectors or brackets) to allow the pan to be removed. I did however have a T30 screw to remove adjacent to front right (looking towards the front of the car) pan bolt.
5. I did the ATF change at 4 years / 32,000 kms, and would describe the old fluid as 'somewhat' discoloured and there was also some definite sediment sitting on both magnets.
6. Improved smoothness and responsiveness of the transmission after the service was noticeable to me. (Hopefully not placebo effect).
7. My crankshaft pulley nut took a 27mm socket, and with a long breaker bar, could be turned (clockwise from the front) from underneath the car (transmission in neutral and the car was on a hoist).
8. My car, having the later 7G-TRONIC PLUS, took MB 236.15 ATF.
9. I changed the diff oil at the same time (I'm a change all the fluids by 4 years guy). This was very straightforward. Bought a short 14mm Hex socket on-line to access the drain plug, and it took a full 1.2L of Fuchs Titan Sintopoid FE SAE 75W-85.
I trust these tidbits help encourage others to complete this very worthwhile maintenance and / or avoid some needless aggravation.
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