722.9 Please help, I'm going nuts!

[Technoholic]

If adaptation won't fix it, the operation of multidisc brake B2 is faulty. It could be the solenoid that switches that brake, but you can't buy solenoids for the 7G separately from the valve chest sadly. The B2 brake is locked for gears 1,2,3 and 4. It unlocks for 5 and remains unlocked for 6 and 7. It only re-engages when 5-4 down change happens.

what’s the fix for this if the solenoid can’t be replaced? Can this be fixed with a valve body and/or TCM rebuild or does it need a whole replacement from MB?

 

[Uncle Benz]

I think it’s going to need the transmission opening up to take a look. It’s possible the friction discs in the B2 are worn, but maybe I’d look at the solenoid first. The characteristics of each solenoid are set in the control module when it’s made according to MB, and they cannot be replaced individually. Or so they say. I do know that some of the solenoid valves are normally open and some are normally closed, so you can’t swap them around willy nilly.

It improves when its hot, so my feeling is that it’s to do with oil flow more than mechanical wear, but that’s just a hunch.

 

[V6Matty]

I think it’s going to need the transmission opening up to take a look. It’s possible the friction discs in the B2 are worn, but maybe I’d look at the solenoid first. The characteristics of each solenoid are set in the control module when it’s made according to MB, and they cannot be replaced individually. Or so they say. I do know that some of the solenoid valves are normally open and some are normally closed, so you can’t swap them around willy nilly.

It improves when its hot, so my feeling is that it’s to do with oil flow more than mechanical wear, but that’s just a hunch.

Think I’d agree that’s it’s something to do with oil flow, I wonder how many of these boxes had a judder fix fluid applied by previous owners to mask the issue and over time it’s clogged a few of the oil galleries?

 

[dry run]

If adaptation won't fix it, the operation of multidisc brake B2 is faulty. It could be the solenoid that switches that brake, but you can't buy solenoids for the 7G separately from the valve chest sadly. The B2 brake is locked for gears 1,2,3 and 4. It unlocks for 5 and remains unlocked for 6 and 7. It only re-engages when 5-4 down change happens.

Great knowledge

 

[Uncle Benz]

Great knowledge

I went on a 722.9 refresher course in October

Just had coffee with Mike (my auto guru). He agrees that the B2 friction discs are likely to be ok, and it’s most likely an oil flow problem. He said solenoid would be his first port of call. He says you can change them, but it’s not widely spoken about.

 

[Technoholic]

I went on a 722.9 refresher course in October

Just had coffee with Mike (my auto guru). He agrees that the B2 friction discs are likely to be ok, and it’s most likely an oil flow problem. He said solenoid would be his first port of call. He says you can change them, but it’s not widely spoken about.

Is this someone I can get in touch with? I’d like to understand how and where I can do this. I’ve seen many solenoids for sale but obviously I can’t imagine it’s as easy as buying a new one and swapping over. Plus I don’t have the facilities to drain oil to remove the pan etc.

 

[Uncle Benz]

PM’d

The way these things work, the solenoid isn’t just switched on on off. It’s a pulse width modulated signal. That’s what the shift adaptation adjusts. You are essentially slurring the way the valve moves from closed to open state. If the solenoid is faulty it doesn’t matter how much you adjust the signal, you won’t resolve the problem. On the 722.6 the torque converter lock up clutch solenoid is the one that usually goes. It gives a bump at 1600rpm as it locks. Changing the solenoid cures it. The more I think about it the more I fancy the solenoid for this.

 

[Technoholic]

PM received. Thanks.

What are the symptoms of a TCM failure? If it’s not that and the adaptation doesn’t work then I’m leaning towards solenoid too. It’s annoying it’s not a DIY job, or at least not with my tools and lack of lift

 

[kid-jensen]

Here's an idea.

You've spent a 4-figure (upwards) sum in investigative work so far, right?

Plan of action:-
1. Sell the car when the gearbox is hot.
2. Look up the price of an identical car on Autotrader, ebay etc. If you can get a relatively identical one to yours for less than your selling price plus the amount spent on investigations, buy it.
3. Problem over. AND you'll know what to look out for on the test drive in the Gearbox department.

I'll bet if you sold/bought before any of the specialists got their spanners out, you'd have a perfect car (well, near-as) and would have spent far less cash in the process.

 

[Technoholic]

I almost certainly would have got a "Better" car if I had done that, but life doesn't always work that way. I did actually consider doing this before knowing whether the problem would be a simple fix or not, but my main issue is that even looking at cars costing 3-4k more (which is more than I've spent anyway), I haven't managed to find a single other CLS 350 with the spec of mine, and then I stopped looking. Right now, I have spent the money, I'm probably not going to spend anymore or very little, so there's no point in selling it now.

I will wait for a while, then trade it for a CLS 63 which was always my long term plan anyway

 

[D5meister]

If u do venture in there and pull the solenoids one at a time. You use a rare earth magnet over the mesh strainer on the end of the solenoid. This pulls fine metal particles out and is normally enough to get them going again.
Probably the crap in the mesh does not allow enough atf flow thru the solenoid valve when atf cold (thick) . But ok when hot (thin)

 

[Technoholic]

If u do venture in there and pull the solenoids one at a time. You use a rare earth magnet over the mesh strainer on the end of the solenoid. This pulls fine metal particles out and is normally enough to get them going again.
Probably the crap in the mesh does not allow enough atf flow thru the solenoid valve when atf cold (thick) . But ok when hot (thin)

I had read that and want to try that but I just don’t have the facilities to do it at home. If anyone has a spare car lift to rent out let me know!

 

[bembo449]

I replaced the TCU in my 221 on a pair of car ramps pal , so have other members , it was straight forward enough with a bit of guidance from chaps on here

 

[D5meister]

There are some good vids on tube. Will post link when have more time.

 

[D5meister]

useful cleaning vid as promised..

 

[mattkh]

..... and over time it’s clogged a few of the oil galleries?

When doing a ATF change, would a flushing oil unclog them. Is it recommended?

 

[D5meister]

I am unclear why the main pan filter does not catch the metal fur that gets stuck in the solenoid meshes?

It may be from the pump impellor (assuming the filter is before the pump) and so the metal gets free passage to cause blockages?

I would like to see more magnets in there, and the silver type (Neodymium Iron Boron - with nickel flash) installed before the solenoids, so the oil to them has no metal fur.

Simple retro fix for gifted Auto wizard.

 

[Mark A]

When I did the first ATF change on my ML (previously done by garage), I found that there were no magnets installed on the pan. Not sure how common that is but makes sense to have a few in the pan.

 

[D5meister]

I may invest in a few stronger ones the same height, maybe wider, shame there are not too may steel items inside the box to fix more in.
As the bulk of the magnets are in the tray, the pan filter will filter metal bits out as the ATF gets sucked up to pump round again So adding magnets to the tray may prolong the filter lifetime by a tiny amount, over and above existing ones.

There is another one on a sliding switch bar in the box - more dissembly required to clean that one. Bit more than Im prepared to do TBH.

 

[D5meister]

If you pause the vid at 1:49 he gets an alarming amount of metal from the mesh. Tempted to look at mine when apart.