722.6 gearbox help

[Rich764089]

Hi. My 722.6 gearbox gets stuck in gear and goes into limp mode on occasion under hard acceleration. No engine lights. I can't change between C and S when it happens.

Grateful for suggestions on where to start with diagnosis. Not yet had a chance to get to garage for fault codes. I guess it's also possible it's not gearbox related....?

 

[DSM10000]

Have you checked the fluid level and when was the transmission fluid last changed?

 

[Rich764089]

Short answer, no and not sure! This was my first port of call and will get it changed ASAP.
But could that be the cause?

Thanks for reply.

 

[Petrol Pete]

722.6 is a tough old beast , used in all sorts of vehicles including trucks , all the way up to V12 Merc's . If you have no service history simply get it serviced ( as suggested , checking ATF fluid level is the first thing you should do) . If the plug is leaking internally it can behave erratically , also a cheap and easy fix.

 

[alabbasi]

low voltage could cause this, as a failing conductor plate or the plug shown above. Brake switch can also cause this. You need to plug it into a decent scanner and pull codes.

 

[DSM10000]

722.6 is a tough old beast , used in all sorts of vehicles including trucks , all the way up to V12 Merc's . If you have no service history simply get it serviced ( as suggested , checking ATF fluid level is the first thing you should do) . If the plug is leaking internally it can behave erratically , also a cheap and easy fix.

View attachment 143651

Good call. The plug is around £20 and will come with an updated seal

 

[DSM10000]

Short answer, no and not sure! This was my first port of call and will get it changed ASAP.
But could that be the cause?

Thanks for reply.

Low fluid can cause change issues.

It could be faulty solenoids as well but start with the simple stuff, check the level first.

The fluid needs to be at 85 deg C when checking the level.

 

[Rich764089]

Thanks very much for all the really helpful replies! I'll get the fluid and plug changed as soon as I can and hope that fixes it.

 

[Rich764089]

722.6 is a tough old beast , used in all sorts of vehicles including trucks , all the way up to V12 Merc's . If you have no service history simply get it serviced ( as suggested , checking ATF fluid level is the first thing you should do) . If the plug is leaking internally it can behave erratically , also a cheap and easy fix.

View attachment 143651

I was surprised I had issues as I know it has a reputation for robustness. I have it with the

 

[Rich764089]

Posted too early.

Mated to the M275, so was wondering if the torque could be a factor long term (800nM plus). But I know they kept the 722.6 for this engine as it could handle this torque.

 

[Petrol Pete]

It was also fitted to the SLR McLaren and the CL V12 in W5A form (rated to around 600Nm) Because the 7G couldnt handle it and was unnecessary with all that torque available.

If yours has 800Nm and is stock I would assume MB built the transmission to take it, with regular servicing.

 

[NIKC43AMG]

Hi. My 722.6 gearbox gets stuck in gear and goes into limp mode on occasion under hard acceleration. No engine lights. I can't change between C and S when it happens.

Grateful for suggestions on where to start with diagnosis. Not yet had a chance to get to garage for fault codes. I guess it's also possible it's not gearbox related....?

I had similar problems after car came back from gearbox specialist, had shaft seal replaced along with new oil cooler it’s a c43/98 wouldn’t shift out of 1st, when I took it off the transporter,they took it back, said it was fine on various test drives they drove back it back to me 50 miles, I took for test drive felt like it was pulling away in 3rd wouldn’t shift on lever from 5 to 4.
They took it back couldn’t find anything wrong no codes took it to Mercedes no codes, they did experience it not shifting from 1st once, turned off and on again and it was ok drive back to me been ok since that was a few months ago now only fine about 500 miles notice it’s leaking oil again have to get in touch so they can take it back, a few places said it could be various things like people have mentioned here I never found out what was the cause of problems other than a specialist did mention pressure as my box was leaking for about 10 years only drove a couple thousand miles a year, he said the box might not be shifting because of the pressure, no idea nagar it was maybe they hadn’t filled up
Properly and didn’t want to seem like they had messed up.
Very sceptical about having leak fixed again incase it causes shifting problems again.
Sad thing is it can cost thousands and still not find what’s wrong sorry I’m not much help but your not alone in experiencing problems shifting

 

[Petrol Pete]

I have linked this numerous times on here. It's long , but it's all you need to know about this transmission . Delves way deeper into it than most of us would ever go.

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[Petrol Pete]

Every time I watch any part of this video I think to myself what Frucking nutpiece Mercedes Benz employee(s) decided that this piece of electro/mechanical tech would last 'a lifetime' with never needing an oil and filter change.

Whoever it was I can guarantee you he/they wouldn't know one end of a centre punch from a hammer .

I say 'he' because no woman in her right mind would make a dumbass decision like that

 

[Rich764089]

Sorry to hear of your woes Nik.

Pete.... Also a high chance it was a man because most of those techs are men!

 

[Rich764089]

Very belatedly following up on this. I had the gearbox fluid changed and all seems well. Fingers crossed. Thanks all for advice, as ever.

I'm actually probably gonna to be selling the car soon, as I just don't have the time to use it any longer. So if anyone wants a fairly-rare-now biturbo V12 W220 S600 with a silly amount spent on it in the last few years, give me a shout