722.9 w/ MCT transmission flush

[C63Sam]

Hi all, hoping somebody can help me with something I've been searching for an answer too all over the internet & coming up blank; I recently took ownership of a C63 Coupe with the 7-speed 'Speedshift' transmission that is equipped with the wet clutch setup rather than the more traditional torque converter. The transmission has never been serviced so far as I can tell, (not great but not a lot I can do now) so I'm planning to et the fluid & filter changed ASAP. I've watched a few videos and it doesn't look too bad, I have an iCarsoft tool which should ensure I top up to the correct level, however I understand that by just dropping the pan off then refitting & refilling I will only drain ~5 litres of fluid, whilst the total capacity of the system is 7.1 litres.

I know this is all Mercedes would do if I took the car to them, but the fact the car is overdue for this by quite a few thousand miles makes me want to be a bit more thorough if I can be - I have seen videos of people with torque converter equipped cars fully 'flush' the system by removing the oil cooler return line at the gearbox and running the car in short intervals to pump a small amount of fluid out at a time, and topping up with new fluid between each drain (see this video for reference from 12:30 onwards

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). From my research I see there is no way to drain the wet clutch like there is the torque converter, does anybody with experience of the job know if doing this will allow me to get out the additional 2 litres or so of oil that otherwise wont drain just by taking the pan off? I know the cooler is thermostatically controlled, but I assume there must be some sort of bypass in the system? I don't really want to do it if it has to be done with the oil at 90+ Celsius, I know that means there will always be at least a few ml in the cooler itself I wont be able to change out but if I can still get a lot more out doing it this way then it would be worthwhile IMO. If not, I'll probably just do another change in a few months time after all the oil has been mixed up again, but I must admit mixing 5 litres of good oil with 2 litres of bad oil just doesn't feel right to me as an engineer.

 

[Petrol Pete]

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Hello and welcome . The first part of this vid shows how the experts do it , Elsewhere on Motor Zimmer there is a video showing the full thing. If anything I would expect a fluid change to be 'easier' on an MCT box as there is no torque converter to hold any old oil . The 7g boxes (I believe) have a drain on the TC . The vid you posted is showing a basic 7g service . The internet has many on how to pump fluid (flush) through the cooling circuit.

I agree , the thought of litre or more of old oil in the new oil doesn't sit well with me either so have pity on a bloke who owns a car that back in the day someone thought omitting the drain plug on the TC was a good idea !

 

[Bellow]

Don't know if this well help...... I recently changed the fluid on my (not MB) auto box and flushed the TC at the same time.

First point to note - when the cooler line is removed the fluid will drain from the cooler. So draining the cooler is possible. Just bear in mind that whatever method you are checking the fluid by you won't have an accurate reading until the fluid has been hot enough to open the thermostat and reach (and refill) the cooler. (In my case as I also took the opportunity to fit an external thermostat it was several (winter) days and a very long climb up a hill before it opened. The level on the stick went from 'high' hot to 'low' hot. A top up sorted that).
At a guess your thermostat will be within the gearbox so as you suggest the fluid would have to be at temperature for any external flow. On a TC auto box the flow to the cooler is immediately from the TC (the TC is the primary input of heat to the fluid) but a wet clutch could be configured differently. AFAIK it doesn't need fluid circulated through (as per a TC). Where a wet clutch will hold fluid will be in its operating chambers - see below.

So, with the fluid from the pan and the TC I had all the old fluid out? Not quite. There was still a litre or so in the box itself residing in the servos, accumulators, etc. I was told of a way to get it out. It involves raising the drive wheels and with the pan still removed and engine running, cycle through all the selector positions. That method though will run it dry. Alternatively the pan can be re-fitted and enough oil added to cover the filter pick-up and then drained again. Also it isn't enough to merely go through the selector positions but also run the plot at speed enough to permit selection of all the gears.
I was told though that chasing down the last litre (in 14 litres) just wasn't worth the grief so I took the advice and skipped it.

This is what I was told:
''"I" wouldn't--and didn't--bother to flush the servos, accumulators, clutch piston housings, etc. It's just not that important. There isn't a lot of fluid trapped there. AND, you'd have to spin the output shaft high enough to engage Overdrive, in order to flush the Overdrive fluid circuit. This is unreasonable, because with the output shaft spinning at ~50 mph, you've got to have lube in the geartrain. I change the fluid in the pan, I flush fresh fluid through the converter, and maybe flush fresh fluid through the cooler(s), and call it "good enough".

and
''As I have already said--what's left in the trans accumulators/servos/fluid passages/valve body/piston housing is INCONSEQUENTIAL. I bet it's less than a quart. Probably half-a-quart. I've never tried to measure what comes out of a transmission that's being disassembled. It makes a big mess, a large puddle on the work bench...but half-a-quart makes a big puddle.''

The proportion left in your box is higher than with my 14l capacity (half and half box and TC) but as far as I can see without making the box go through a full cycle of change pattern it stays where it is. I suspect the advice given to me applies to you also. I have no regrets about following it.

 

[Petrol Pete]

as Bellow says ^^^^ or if you really wanted to go the whole hog you could do the change , drive around for a few miles then vacuum as much fluid as you can out of the box and replace it with the exact same amount of ATF.

Costly in fluid but it will almost certainly be cleaner , but by how much is debateable . Next option is to remove and dismantle transmission completely ! no thanks.

 

[C63Sam]

"Next option is to remove and dismantle transmission completely"

I sincerely hope not lol!

I think my best option is to just start the job prepared and see how it goes. going to buy a couple of o-rings incase I do end up with the return pipe off the side of the gearbox and ample fluid for flushing purposes. I've seen plenty of videos where people have drained out of the return line with the engine idling whilst topping up into the sump and eventually got brand new fluid coming out of the cooler return, (on TC cars given, not MCT), so I'm not sure removing the return line would drain the cooler and prevent it refilling, Id more likely suspect there is some sort of bypass system, although I simply don't know whether fluid goes from the wet clutch to the cooler & back to the pan during 'normal' operation as it would with a TC, it may even just drain into the pan when you switch the engine off and all drain out when the sump is removed.

I'm going to get a bucket from B&Q that is marked for fluid level internally and use this to capture everything I get out, if I can get ~6 litres out (leaving only ~1 litre left) just taking the sump off, I think id be happy to just top up with fresh fluid & a new filter, if its more like 5 litres I get out then I'll probably consider trying to flush it through the cooler eg. Running the car with the line disconnected makes me nervous and will likely be awkward stopping & starting the car whilst trying to keep tabs on the amount of fluid draining as Ill be doing this on my own, though one big advantage I'll have in this respect is the coolant return line is on the drivers side in the UK, so I may be able to just lower the lift right down and kneel next to the car so I can keep tabs on what's happening underneath and just reaching up into the cabin to turn the engine on/off

 

[Bellow]

"Next option is to remove and dismantle transmission completely"

I sincerely hope not lol!

I think my best option is to just start the job prepared and see how it goes. going to buy a couple of o-rings incase I do end up with the return pipe off the side of the gearbox and ample fluid for flushing purposes. I've seen plenty of videos where people have drained out of the return line with the engine idling whilst topping up into the sump and eventually got brand new fluid coming out of the cooler return, (on TC cars given, not MCT), so I'm not sure removing the return line would drain the cooler and prevent it refilling, Id more likely suspect there is some sort of bypass system, although I simply don't know whether fluid goes from the wet clutch to the cooler & back to the pan during 'normal' operation as it would with a TC, it may even just drain into the pan when you switch the engine off and all drain out when the sump is removed.

If you remove the in and out lines at the gearbox for the cooler, the cooler will just drain by gravity. That's all that's needed - old fluid out.
It's only flushed by pumping on a TC auto because of the TC and only possible (without further complication) when there's no thermostat. Remember the cooler will be empty until full temp is reached if there is a thermostat is in the box. You can feel the lines for the 'stat opening and adjust the oil level accordingly once they are warm to the touch.

I suspect you are correct re wet clutch just draining back to the pan. A TC has to be pressurised to avoid cavitation. Chances are the wet clutch is just in a wet environment (like a bike clutch) and the only pressurised fluid it sees is for control purposes - not volume flow.

I'm going to get a bucket from B&Q that is marked for fluid level internally and use this to capture everything I get out, if I can get ~6 litres out (leaving only ~1 litre left) just taking the sump off, I think id be happy to just top up with fresh fluid & a new filter, if its more like 5 litres I get out then I'll probably consider trying to flush it through the cooler eg. Running the car with the line disconnected makes me nervous and will likely be awkward stopping & starting the car whilst trying to keep tabs on the amount of fluid draining as Ill be doing this on my own, though one big advantage I'll have in this respect is the coolant return line is on the drivers side in the UK, so I may be able to just lower the lift right down and kneel next to the car so I can keep tabs on what's happening underneath and just reaching up into the cabin to turn the engine on/off

It's not for the fainted hearted (I reminded myself of this this afternoon during a PAS flush) and isn't worth it for a cooler (which should self drain by gravity - have a bucket ready for it).
The flow rate through these systems is significant and keeping up replenishing is not easy.

With the fluid from the pan and what drains from the cooler - that only leaves what's trapped in the gearbox internals (and hard to move). That's a good result when you consider that that box when coupled with a TC may only get half its fluid changed at a time.

 

[jasonh]

I had my MCT oil changed by a specialist who I have confidence in. He said he could only get 5 litres of new fluid in. I absolutely could have done it myself (I've done a few BMW gearbox oil changes) but I wanted the "stamp in the book" and it recorded on the DSB. It also cost around £230 and the parts alone would have cost me £150.

Most ZF gearboxes (BMW, Rolls Royce, Audi, Jaguar, Range Rover) have no drain for the TC so you always only change 2/3 of the oil. I suspect the oil change interval factors this in.

Gearbox oil is messy smelly stuff so if I were you I'd just do two oil changes. Getting the oil level right is actually pretty easy. The pain with doing two changes is you'll need to take the sump off to refit the tube that sets the oil level. That means technically you'll need two sets of sump bolts. They're one time use.

 

[Bellow]

Maybe no thermostat if it has a saddle cooler?

 

[C63Sam]

Right, thought the polite thing to do was update this since you were all good enough to offer advice to me! I did the change last week, drained out between 4.5-5 litres (measuring with a scale on the inside of a bucket), + allowance for spillages etc. The old oil was dark, black almost, but I don’t think it would take much to do that to this ‘new’ blue fluid vs the old red stuff, other than the colour it didn’t seem too bad. My magnets had picked up quite little debris, I’d seen videos of cars serviced at the correct 40k interval look the same as mine so I was happy with that at 75k & it gave me confidence there ought to be no contamination in the system hopefully.

having nobody on hand to help me, and the reasonably good condition of my magnets etc, I decided against trying to drain any other lines by running the car. More hassle than it was worth I figured and I could always do another flush if I so wished. All I can say is wow, what a difference this has made to the car.

ive had several mercs before this so I already knew they aren’t exactly renowned for their smoothness in the gearbox department, but mine had been particularly ‘jolty’/‘clunky’ at times in the C63, especially in comfort when pulling away and changing up into 3rd/down into 2nd at low throttle it occasionally felt so nasty it made you cringe. I had put it down as a characteristic of the wet clutch, having never experienced a merc equipped with one before, however the difference after getting new fluid & filter in is night & day. I had seen comments elsewhere that fresh fluid would make gearshifts smoother, but thought it would be marginal at best, I wanted to change the fluid purely from a maintenance point of view as I loved the car regardless but I am so satisfied that such a simple job has yielded such a great improvement in the feel of the car.

i guess to sum up, for anybody sweating about draining out every last drop of their transmission fluid, I simply wouldn’t bother, especially if the car is an MCT model, just changing out the fluid that can be drained following the normal procedure has been more than sufficient for me.

will try to attach a pic of my sump magnets:

 

[Spider10]

My MCT box is as smooth as a baby's bum in all modes glad you sorted it
Enjoy

 

[W1ghty]

Good job buddy

 

[Bellow]

ive had several mercs before this so I already knew they aren’t exactly renowned for their smoothness in the gearbox department, but mine had been particularly ‘jolty’/‘clunky’ at times in the C63, especially in comfort when pulling away and changing up into 3rd/down into 2nd at low throttle it occasionally felt so nasty it made you cringe. I had put it down as a characteristic of the wet clutch, having never experienced a merc equipped with one before, however the difference after getting new fluid & filter in is night & day. I had seen comments elsewhere that fresh fluid would make gearshifts smoother, but thought it would be marginal at best, I wanted to change the fluid purely from a maintenance point of view as I loved the car regardless but I am so satisfied that such a simple job has yielded such a great improvement in the feel of the car.

Good to see you got it changed and the improvements its brought.
One reason I changed my fluid (non MB) was in the hope of smoother upshifts at part throttle but it made no difference. What did finally tame the box was re-instating a missing fuse that fed the MAF sensor. The MAF hadn't been working and it is from it that the ECU controlling (line pressure for) upshifts takes its primary input. I've no idea what inputs MB boxes read but for certain, it is worth keeping all the engine sensors in good condition for the sake of the transmission alone.

 

[SLSWE]

Instead of creating a new thread I am asking here.
Do you guys recommend to flush + change the tranny fluid or simply change it? I have a 2011 PPP C63.

 

[jasonh]

These gearboxes seem pretty robust with just regular oil changes so I don't think a full flush is required.

 

[Bellow]

Instead of creating a new thread I am asking here.
Do you guys recommend to flush + change the tranny fluid or simply change it? I have a 2011 PPP C63.

The 'flush' in this context is to displace the bulk of fluid in the TC (when there is one) and thus get almost all of the old fluid out as opposed to just over half of it if the old fluid is left in the TC. Where possible, I'd flush the TC every time.

As for epicyclic autos with wet clutches - I don't know enough about them to comment.