Bad day, 722.6 transmission in W163 stuck very much in 2nd

[tttonyyy]

Had the ML270 for 18 months now, sorted the swirl flaps and running 100% biodiesel no problem (aside from having to periodically rebuild the high pressure pump - the head seals deteriorate quickly).

Since ownership it has always "slipped" a bit in 4th, IE overrevved - like a clutch band is slow to grab. More recently it's started to go into limp mode (2nd) reporting "improbable gear ratio", which cleared when stopped and restarted.

Now it's permanently in 2nd. And my expensive iCarsoft MB V2.0 had the screen flicker and die so I can't see what else it's reporting.

I've dropped the transmission pan and the valve body, removed and tested the solenoids (they're all fine, as far as I can see). There was quite a lot of very fine metal sludge both stuck to the magnetic trap at the bottom of the pan, and all over the magnetic sensor that peers up into the gearbox (presumably to sense RPM). Not good for a box that has only done 70k.

Additionally, there was quite an ATF leak past the wiring loom bushing.

I've cleaned it all up, put it all back together (with new bushing), put in new ATF (torque converter flushed via pipe on ATF coolant return). But alas, still stuck in 2nd.

I don't really want to give up on the old girl, but I'm at a loss what to try.

Some photos.

Underneath of box with valve body removed. I assume that the rectangular holes visible behind the circular holes are used for RPM sense. That they're in this position perhaps implies that the thrust bearings haven't allowed the shafts to slide them out of view of the sensors?

Valve body, note the magnetic swarf on the RPM sensors:

Solenoid valves out, each was a few ohms of resistance and I blew through them with an airline

All refitted with new pilot bushing and filter:

More metallic sludge from the ATF coolant return

ATF going in

ATF from torque convertor coming out

 

[Doug1234]

My 97 w210 did the second gear and reverse only when the speed sensor/s packed up on the plastic plate.
For a few months it would not go into 4th unless you lifted throttle and it would bang into the lower gears when driving slow in traffic and often stay stuck in 3rd gear.
I replaced the plate but I had to get codes cleared before it would work properly again, apparently it only had an abs code but after clearing it all worked ok again.
I also changed the pressure regulator spring which costs about £1, how to here
https://www.benzworld.org/threads/722-6-pressure-regulator-spring-replacement.1423078/

On mine the magnet nearest the edge of the plate had gone soggy and crumbled inside its cover

So clear codes even if not anything relevant and see if it drives.
Out of curiosity do you dry or water wash your biodiesel ?, I'm around 20k on an om642 in a 06 Jeep GC using water washed bio with no issues other than one injector has started to smoke a bit at idle so is getting replaced but its done 115k so fully expect the others to start getting tired.

 

[tttonyyy]

Thanks for the reply. I wish I could clear the codes - I've e-mailed iCarsoft to see if they can repair my MB 2.0 since it has been rarely used and is only 18m old. Might have to try a local indie to see if clearing the codes helps or not.

Interesting tip on the regulator spring, that could be my 4th slow shift problem - if I end up taking it apart again to replace the plate (seeming likely) I'll have a look. Possibly different part number as this box is a little later (2003).

The biodiesel I just demeth (to 90C), air bubble 24h while it cools, then settle for a few weeks, then 1u cold filter before it goes in the tank - with a splash of 2-EHN to give it some kick in the colder months. The key to good fuel I have always put down to getting a bright clear Jan Warnquist 3/27 test pass, IE complete conversion. I think any bi/monoglycerides hold onto soap and moisture in the settling process otherwise.

 

[Doug1234]

The spring in mine was if I remember correctly in about five bits and these bits wind themselves onto each other making the spring shorter, mine was nearly 15mm shorter than the new one.
Biodiesel I water wash but its done at whatever the ambient temp is and when done just heated to above 70c then cooled and filtered.
Find the Jeep is happy with 100% bio , much better with some 2ehn added, but add about 15% diesel to that mix and its like being fired out of a catapult when you stamp on it... this I expect is the diesel getting the bio burning quicker.

 

[tttonyyy]

In my early bio days I had problems with blocking filters when mixing bio and diesel. Possibly because the quality was poor when I started out (2007). Suspect the diesel was causing some residual glycerol or soaps to precipitate. I've avoided doing that ever since, though in some chiller months I've mixed in a little petrol to keep the viscosity down - but always mixed in a container and settled, never in the tank out of paranoia. Sounds like a bit of diesel is helping you with lowered viscosity and improved atomisation in the injection process.

 

[Doug1234]

Could it be the petrol giving the head seals a short life ?.
I have always mixed petrol over the years to thin down veg for water settling before filtering or a veg bio mix in all the other cars in really cold winters I have owned but won’t be putting any petrol near the Jeep.
Last couple of winters it ran 100% bio most of the time, aside from a little puff of smoke on a cold start it was fine.
The diesel I add just seems to get the bio burning quicker , 100% bio feels like engines down about 15-20 on power , viscosity's fine it just doesn’t lite up as quick as diesel.

 

[tttonyyy]

Ah! I can answer that - no because I've never put any petrol in with biodiesel in the Merc.

 

[tttonyyy]

So, new information along with a new code reader...

P2502 historic, the gear is unreasonable or the transmission is slipping
P220A current, the speed comparison of Y3/6n2 to Y3/6n3 is unreasonable

Cleared them both and now it changes gears OK again, went for a reasonable drive and all seemed well as the box warmed up.
Then, suddenly threw a P2502, however that one seems to clear OK with ignition cycle. This happened once more.

So I am guessing that P220A cannot be cleared with ignition cycle and this one was causing the apparent "stuck" in 2nd behaviour.

Looking at sensor Y3/6n3 it seems to drop to 0 rpm sometimes while driving, in fact the data out of it looks quite erratic. Y3/6n2 looks more reasonable. But I'm just guessing based on no experience. Are these the hall sensors on top of the conductor board that read the coded wheels in the box? Input and output shafts?

Since it's back to semi-drivable now I think I'll change the conductor plate and see if that helps. I've also ordered a replacement valve body spring in case one of them is broken (it still showed some evidence of slipping changing up to 4th, but this didn't trigger the P2502 code).

 

[Doug1234]

Y3/6n2 and y3/6n3 are indeed the speed sensors so the new plate should fix your problem.
Until its been changed you may get some other weird faults like not being able to select any gear at all with the selector before driving off but ignition off and on again will cure that.

 

[tttonyyy]

New electroplate fitted, checked all the springs under all the plates (they're all intact). Washed the loom plug thoroughly in Isopropyl Alcohol to remove any remaining ATF from the leaking pilot bushing. Washed the new bushing in Isoproply Alcohol again to remove traces of ATF that came back out of the loom. Fitted it back together and refilled.

Took it for a drive and again, when it gets warm - P2502 "the gear is unreasonable or the transmission is slipping". It seems to happen more often than not pulling away around a corner and without any actual evidence of slipping. There's a corner near me (have to pull away fairly hard, left, up a hill) that seems to trigger it.

I'm beginning to wonder if my aftermarket ATF dipstick isn't representative of what the actual ATF level should be, and maybe the box is just underfilled - and when it's hot/runny it just slops to the side of the pan and the drain ports in the valve block more quickly deplete the fluid available. So I've ordered some more ATF and I'll top it up further than my aftermarket stick seems to recommend.

I presume Mercedes lack of supplying a dipstick is to force customers to return the dealership for servicing (or because it's supposedly "lifetime" ATF) and didn't anticipate people like me trying to keep old examples on the road.

If this doesn't work I'm not sure where to go. Replace the valve block? I'm getting tired of draining and stripping the transmission now. Replace the whole transmission where you end up with a second hand unknown with many more miles on it than mine? Or a transmission rebuild at great expense that might not fix the problem?

Or I just give up on this one and buy something else.

 

[tttonyyy]

Oh and I checked the encode wheels, it's the same as this chap reports:
https://www.benzworld.org/threads/722-6-transmission-rpm-sensor-problem.1238434/
Front one very tight and second one a small (very small) amount of axial movement. Rotating them results in more ATF pouring out of the holes in the bell housing, into your face if you're not paying attention

 

[Oldspanners]

New electroplate fitted, checked all the springs under all the plates (they're all intact). Washed the loom plug thoroughly in Isopropyl Alcohol to remove any remaining ATF from the leaking pilot bushing. Washed the new bushing in Isoproply Alcohol again to remove traces of ATF that came back out of the loom. Fitted it back together and refilled.

Took it for a drive and again, when it gets warm - P2502 "the gear is unreasonable or the transmission is slipping". It seems to happen more often than not pulling away around a corner and without any actual evidence of slipping. There's a corner near me (have to pull away fairly hard, left, up a hill) that seems to trigger it.

I'm beginning to wonder if my aftermarket ATF dipstick isn't representative of what the actual ATF level should be, and maybe the box is just underfilled - and when it's hot/runny it just slops to the side of the pan and the drain ports in the valve block more quickly deplete the fluid available. So I've ordered some more ATF and I'll top it up further than my aftermarket stick seems to recommend.

I presume Mercedes lack of supplying a dipstick is to force customers to return the dealership for servicing (or because it's supposedly "lifetime" ATF) and didn't anticipate people like me trying to keep old examples on the road.

If this doesn't work I'm not sure where to go. Replace the valve block? I'm getting tired of draining and stripping the transmission now. Replace the whole transmission where you end up with a second hand unknown with many more miles on it than mine? Or a transmission rebuild at great expense that might not fix the problem?

Or I just give up on this one and buy something else.

You seem to be almost there, the only thing you haven't mentioned is the ATF temperature when you checked the level. The only other thing I can mention is just how bad was the oil leak into the wiring, I've "read" that it can wick up to the TCU.

 

[joderest]

have to ask, when an Indy changed my gearbox fluid at 40,000, the stuff he put was not red like ATF, more a normal oil colour.
Are you using the correct grade of oil ?
My ML is now at 55,000, so do hope it goes on a bit longer.

 

[tttonyyy]

have to ask, when an Indy changed my gearbox fluid at 40,000, the stuff he put was not red like ATF, more a normal oil colour.
Are you using the correct grade of oil ?
My ML is now at 55,000, so do hope it goes on a bit longer.

Good question - I think the spec for the box is MBZ 236.10. I used Mannol AG52 which is MBZ 236.10/236.11.
It is the red you would normally associate with ATF. But the problems were like this before changing the ATF so I'm not to worried on that front. It is quite possible that by filling the box to the level it was when I started was wrong, because plenty may have leaked out past the pilot bushing.

I always check ATF level with engine on in neutral when up to temp. But knowing what that level is supposed to be without a proper dipstick is bit of a guess.

Speaking of which, mine is an eBay cheapo, it does have the diamond in the end like some posts allude to, but I still think it's guesswork.

Too little ATF I read is associated with hard gear changes, overrevving on change and sluggish change between forward and reverse (which I have had sometimes after it has stuck in 2nd).

 

[umblecumbuz]

Brings back a memory.
I've done three of these boxes, and I had an original dipstick which of course I kept for the next car when i sold a previous one (all 722.6 boxes). The dipstick went with the sale of the last car, but ... at the time, there was a Youtube vid giving measurements for anyone wanting to make their own dipstick. I made one at one point out of net curtain wire and marked it up.
Malcolm (Television), now deceased, posted measurements for fluid levels for the 722.6 box. A trawl through his original posts will find them - but be warned, he was a prolific contributor!

There is an alternative. If you really think your fluid level is on the low side, causing your current troubles, then why not add atf in easy stages while monitoring any changes in the box behavior. If you reach a point where it feels better, mark your present dipstick accordingly.

 

[Oldspanners]

Good question - I think the spec for the box is MBZ 236.10. I used Mannol AG52 which is MBZ 236.10/236.11.
It is the red you would normally associate with ATF. But the problems were like this before changing the ATF so I'm not to worried on that front. It is quite possible that by filling the box to the level it was when I started was wrong, because plenty may have leaked out past the pilot bushing.

I always check ATF level with engine on in neutral when up to temp. But knowing what that level is supposed to be without a proper dipstick is bit of a guess.

Speaking of which, mine is an eBay cheapo, it does have the diamond in the end like some posts allude to, but I still think it's guesswork.

Too little ATF I read is associated with hard gear changes, overrevving on change and sluggish change between forward and reverse (which I have had sometimes after it has stuck in 2nd).

I've used an ebay one which seems to do the job the main difference you'll find to the level is temperature which you can measure with your icarsoft if it's working again.

 

[tttonyyy]

Ah good tips from both of you, and on the checking the temp via diagnostics to be sure.
Well I've put some in and *touch wood* it hasn't misbehaved since. Which is tempting fate, I know. Perhaps when an air bubble gets pulled through the valve block bad things happen.

I was also wondering about that filter that pushes up into the valve block. Does the transmission "suck" the ATF up through that filter foot? Because the last one I fitted had a very loose o-ring seal into the valve block, and when I ordered the conductor plate it came with another filter, which was a slightly different design and a much tighter fit. I guess if it's loose enough and the fluid doesn't cover the base of the valve block this is an obvious place for air to get sucked in and mix with the ATF, potentially causing the odd behaviour I've seen.

Also, and I completely forgot to mention this - when I was taking out the little 4Nm bolts capping the valve springs, one of the plates had three loose bolts. I'm sure that didn't help either.

 

[Oldspanners]

Ah good tips from both of you, and on the checking the temp via diagnostics to be sure.
Well I've put some in and *touch wood* it hasn't misbehaved since. Which is tempting fate, I know. Perhaps when an air bubble gets pulled through the valve block bad things happen.

I was also wondering about that filter that pushes up into the valve block. Does the transmission "suck" the ATF up through that filter foot? Because the last one I fitted had a very loose o-ring seal into the valve block, and when I ordered the conductor plate it came with another filter, which was a slightly different design and a much tighter fit. I guess if it's loose enough and the fluid doesn't cover the base of the valve block this is an obvious place for air to get sucked in and mix with the ATF, potentially causing the odd behaviour I've seen.

Also, and I completely forgot to mention this - when I was taking out the little 4Nm bolts capping the valve springs, one of the plates had three loose bolts. I'm sure that didn't help either.

Certainly all you mentioned won't help the smooth running of the transmission but low fluid level will certainly cause problems as will too high. Check it at the correct temperature.
Hope it all stays smooth from now on, happy motoring

 

[umblecumbuz]

When you reckon you've hit the right fluid level in the box (engine running, car level, in P or N, and temperature reached), then mark the fluid level measuring from the TOP of the dipstick tube. That way, whatever dip stick you subsequently use - even a piece of fishing line - you will still get the correct level.

 

[stumo]

Try cleaning your TCM. The atf wicks up the loom all the way to the tcm.