When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I have inherited a 2015 W205 C300 Diesel Hybrid with an OM651 engine and 274.2 HK7C700 transmission. It has 90,700 miles on the clock and to my horror, has never had a transmission service! I have been preparing to do this myself and have organised all of the necessary parts/fluid (Filter, Gasket, Drain Plug, and 2 x 5L MB 236.15 Transmission Fluid) to perform this myself today.
There seems to be a lot of guidance on the transmission's close relative, the 722.9, but very little on this 724.2. As such, I have studied YouTube guides on the 722.9 as a template and have refined my approach using the attached WIS guidance tailored for my 724.2 transmission.
This has led to a few questions that I would be hugely grateful for help with:
As no transmission service has been carried out and the mileage is so high at 90k miles, I'm very concerned that I will have issues soon. Is the transmission doomed to fail sooner than most? Are there any steps I could take in addition to this service to bring it back up to health?
My driveway is on a slight incline and I have lifted the car from the front on two axle stands, with the nose facing uphill. It sounds like this would be a significant problem for not only draining all the fluid out, but also filling it up correctly?
Would you have any recommendations for making this level? I am wary of putting two additional jack stands at the rear as they would have to be placed on a relatively steep portion of the driveway and therefore wouldn't be safe.
Would measuring the amount of fluid that I drain and subsequently filling with that exact amount combat this problem?
It seems my model does not have a drain screw for the torque convertor. Is there a substitute for this in my model to ensure that absolutely all of the oil in the transmission is drained? I feel this is particularly important given how old the current transmission fluid is.
The WIS guidance in the attached "Transmission - 4" file states in step 8 states:
"The transmission must be in transmission
mode S. This ensures that the start-up clutch
remains closed. Otherwise faulty measurements will be made
when checking the oil level."
Is this just a matter of putting it into Sport mode using the Agility select button on the centre console?
Is the transmission doomed to fail sooner than most? Are there any steps I could take in addition to this service to bring it back up to health?
Draining the torque converter may be an additional step for draining all fluid out of the transmission.
Would you have any recommendations for making this level? I am wary of putting two additional jack stands at the rear as they would have to be placed on a relatively steep portion of the driveway and therefore wouldn't be safe.
Just have a level to confirm level of the vehicle. Pretty simple, or just get a shop to carry out this procedure.
Would measuring the amount of fluid that I drain and subsequently filling with that exact amount combat this problem?
No, I would only us this as a reference point. For ex. It's like changing engine oil in the car, it good to have a reference as to how much oil was in the engine prior to the exchange so that you don't overfill. But if you're directly reference just what you took out, then there's always the chance of underfilling or overfilling; but in this case, there's a dipstick of course.
The most accurate way is to make sure the transmission is up to temperature, as in accordance to WIS and fluid (particle theory 101) fluid will expand and contract in accordance to the temperature (You will need a scan tool to monitor the temperature of the fluid)
Is there a substitute for this in my model to ensure that absolutely all of the oil in the transmission is drained?
If this is the case and you're really concerned and don't mind burning money of transmission fluid and screws and gaskets. Redo the transmission service again so that the new fluid and old fluid can be mixed and diluted with new fluid.
Is this just a matter of putting it into Sport mode using the Agility select button on the centre console?
From my understanding, yes.
All in all, you're worrying about nothing. In North America, this has been a very overlooked service generally speaking. You're over by about 30,000 miles if I'm assuming correctly. Not ideal, but having a shop complete this repair may be ideal, might help to bounce idea off with them as fluid exchange is a bit finicky, especially with a hybrid system.
WIS probably states to put the car into S mode, because having the car on ignition will automatically engage the hybrid system first. Putting the vehicle into S mode, just manually overrides to the combustion engine – Just my guess as Bluetec Hybrid's do not exist in North America.
Just make sure you got the correct spec, as per VIN. NOT WHAT PEOPLE SAY HERE
Is the transmission doomed to fail sooner than most? Are there any steps I could take in addition to this service to bring it back up to health?
Draining the torque converter may be an additional step for draining all fluid out of the transmission.
Would you have any recommendations for making this level? I am wary of putting two additional jack stands at the rear as they would have to be placed on a relatively steep portion of the driveway and therefore wouldn't be safe.
Just have a level to confirm level of the vehicle. Pretty simple, or just get a shop to carry out this procedure.
Would measuring the amount of fluid that I drain and subsequently filling with that exact amount combat this problem?
No, I would only us this as a reference point. For ex. It's like changing engine oil in the car, it good to have a reference as to how much oil was in the engine prior to the exchange so that you don't overfill. But if you're directly reference just what you took out, then there's always the chance of underfilling or overfilling; but in this case, there's a dipstick of course.
The most accurate way is to make sure the transmission is up to temperature, as in accordance to WIS and fluid (particle theory 101) fluid will expand and contract in accordance to the temperature (You will need a scan tool to monitor the temperature of the fluid)
Is there a substitute for this in my model to ensure that absolutely all of the oil in the transmission is drained?
If this is the case and you're really concerned and don't mind burning money of transmission fluid and screws and gaskets. Redo the transmission service again so that the new fluid and old fluid can be mixed and diluted with new fluid.
Is this just a matter of putting it into Sport mode using the Agility select button on the centre console?
From my understanding, yes.
All in all, you're worrying about nothing. In North America, this has been a very overlooked service generally speaking. You're over by about 30,000 miles if I'm assuming correctly. Not ideal, but having a shop complete this repair may be ideal, might help to bounce idea off with them as fluid exchange is a bit finicky, especially with a hybrid system.
WIS probably states to put the car into S mode, because having the car on ignition will automatically engage the hybrid system first. Putting the vehicle into S mode, just manually overrides to the combustion engine – Just my guess as Bluetec Hybrid's do not exist in North America.
Just make sure you got the correct spec, as per VIN. NOT WHAT PEOPLE SAY HERE
Thank you so much for the help! Hugely appreciated. Just on the torque convertor - it seems my model does not have a drain plug for it - as confirmed after reviewing WIS and from my local official MB parts supplier. Do you know of any alternative measures that I should take to drain it appropriately? I would assume no drain plug means the system is designed to just drain that oil through the main transmission oil pan too, but thought to query your infinite wisdom. Thank again!!
As far as I know, MB doesn't really call for a transmission service on the regular models. Only the 63 AMGs have transmission and differential fluid changes as part of the scheduled maintenance. I have a friend who owned his own Mercedes shop and he refused to do transmission services on transmissions that went for a long time without a fluid change. It's somewhat common knowledge that sludge can build up over a long time w/o fluid changes in the housing and stick to corners etc. That sludge can come loose when changing the fluid and cause bigger issues. Basically a complete cleaning and rebuild of the transmission would be called for to make sure there's no sludge.
As for the part in the WIS, that's for the AMG MCT variant of the transmission. Your car doesn't have a start up clutch. It has a torque converter. The AMGs with the MCT variant have a start up clutch instead of a torque converter, and they require a fluid change every 30k miles or 3 years, partly because they are tuned for more sporty driving and the transmission undergoes more stress as well as having additional friction material from the start up clutch contaminating the fluid.
Last edited by superswiss; Jan 3, 2026 at 06:51 PM.
They certainly do call for both the differential and transmission service - the below is the prescribed transmission service per the service overview created on WIS using my car's VIN. I have also attached the file for reference, wherein services specific to my car have their service document reference in red text.
Appreciate your insights regarding the requirement transmission service for AMGs with the MCT variant - it makes sense why those have shorter service timelines for their transmissions.
And yes, most in my position find themselves stuck between a rock and a hard place when they've delayed their transmission service. Although I feel in my case, with 90k miles on the clock so 30k miles above the suggested service interval of 62k miles, it would be wiser to service it than go on as is. My hope is to drive this to at least 200k miles and have done a suite of service items from the service sheet already - with a view to then repeating them as and when necessary per the service sheet guidelines.
They certainly do call for both the differential and transmission service - the below is the prescribed transmission service per the service overview created on WIS using my car's VIN. I have also attached the file for reference, wherein services specific to my car have their service document reference in red text.
Appreciate your insights regarding the requirement transmission service for AMGs with the MCT variant - it makes sense why those have shorter service timelines for their transmissions.
And yes, most in my position find themselves stuck between a rock and a hard place when they've delayed their transmission service. Although I feel in my case, with 90k miles on the clock so 30k miles above the suggested service interval of 62k miles, it would be wiser to service it than go on as is. My hope is to drive this to at least 200k miles and have done a suite of service items from the service sheet already - with a view to then repeating them as and when necessary per the service sheet guidelines.
I see. Yeah I've never really locked closely at the non-AMG service intervals. However, the 30k miles over doesn't seem to be the only issue. If this car never had a transmission service, then it's 5-6 years past due. Like the engine oil, there's a time component since oil degrades over time regardless of how many miles you drive. Engine oil should be changed at least once a year regardless of the mileage and looks like the transmission oil every 5 years regardless of mileage. So this car has really old fluid in the transmission.
Yep it's a pickle. I am hoping it was actually performed and is just missing from the service booklet. The 'Major assemblies service card' which is to be expected at the back of the booklet is missing, which gives me hope somewhat. Only way to find out is when I get underneath it tomorrow.
Yep it's a pickle. I am hoping it was actually performed and is just missing from the service booklet. The 'Major assemblies service card' which is to be expected at the back of the booklet is missing, which gives me hope somewhat. Only way to find out is when I get underneath it tomorrow.
honestly, it’s not a pickle and it’s not a problem. But if you’re asking some of these most simple questions, such as how to level the car or if this matters, you need to have a shop do this for you. Your mistakes are a bigger risk than taking it to a dealer.. mechanics that don’t like to change transmission fluid are just covering their asses, but their reality is the fact that they are unable to properly explain to a customer what might happen so they just avoid the risk completely.. as a do it yourselfer, I’ve changed the transmission fluid in every car I’ve had, each which has been used, and which has been up to 240,000 miles of unknown service and old fluids, and never had one issue, not one.
, ever, in 30 years. If there’s sludge in the transmission take care of it and if the transmission doesn’t work, take care of it.. easy. New fluid doesn’t ruin anything, ever. Bad procedures create the biggest problems….underfill, over heat, don’t blame fluid.
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
Slideshow: A one-of-one U.S.-spec Mercedes-Benz SLR McLaren Roadster became even rarer after a factory-backed transformation at McLaren's headquarters.
