Gearbox fluid or knackered?

[Mickey42]

On a hot day last week I did more than the usual 3 miles to work and back for the first time since I bought the car 18 months ago. The box started shifting gear’s (or not)unlike any time before. Since then I’m back to just going to work and back and it’s fine. I’m hoping your comments are going to tell me something about fluid and an easy fix!
Michael

 

[DSK]

Gearbox oil should be changed frequently and don’t trust the tick boxes that say it’s been done. Easiest option is to get it changed despite circa £300-400 outlay after which you will better placed to investigate any further faults should there be any.

As an example I’ve seen service item boxes ticked for stuff that’s never been done and even one of my local MB specialists strongly advising against a gearbox service. It will now go to a different specialist to get it done.


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[FlorinM]

Are there any warning lights in the dash and is the car a lot slower than usual?

 

[Mickey42]

My first indication of a problem was that it kept pulling off in sport mode I.e. first gear rather than second as I always have it in comfort mode. But, this is the third Mercedes I’ve owned and they have all pulled off in first gear until warmed for a few minutes then they pull off in second gear (comfort mode). The transmission fluid change looks like a job I’d be happy to undertake.

 

[Kudly]

ATF service always worth doing. You could also try resetting the gearbox.

 

[Botus]

one indy told me he thought dirty contaminated oil is what causes the electroplate failure to happen earlier in life

as its most often black burnt and full of metal - he might have a point

mine will hold the gear to warm CATS but its never used first if I have it in comfort

is this the car in ur profile or something more modern ? don't forget tractors with a DPF will do odd stuff if trying to regen - 3 mile daily trip = buy a bicycle, we should always aim for a minimum of 10 miles if we start any piston engine - it needs this to get things to temp and to burn of combustion gases and acids that destroy things - to some extent re moisture in oil, etc. same applies to your now broken gearbox

 

[malcolm E53 AMG]

I found those symptoms were the first signs of a gearbox electric plate (speed sensor) starting to fail when I ran my 722.6 5 spd in the E320cdi - starts to occur when the box is fully warm about 11 miles into the journey

 

[rich.g.williams]

On a hot day last week I did more than the usual 3 miles to work and back for the first time since I bought the car 18 months ago. The box started shifting gear’s (or not)unlike any time before. Since then I’m back to just going to work and back and it’s fine. I’m hoping your comments are going to tell me something about fluid and an easy fix!
Michael

Hi, Can you give more details as regards the kinds of misbehaviour you get on a longer trip please?

Starting off in 1st gear - how about what's displayed is it obeying the switch W/S C/S?

No reason to fear the worst as yet,

 

[Mickey42]

Hi all. It always reads comfort mode. It always pulls away in first gear when cold and then pulls off in 2nd when warm. The hot day in question it was dropping into first gear when coming to a stop. To add further information, ever since I’ve had the car, when it comes to a stop whilst warming up you can feel it throw itself back into first gear. I’ve found a Mercedes service kit on eBay for £107, but will it cure the problem?

Cheers

 

[rich.g.williams]

Hi all. It always reads comfort mode. It always pulls away in first gear when cold and then pulls off in 2nd when warm. The hot day in question it was dropping into first gear when coming to a stop. To add further information, ever since I’ve had the car, when it comes to a stop whilst warming up you can feel it throw itself back into first gear. I’ve found a Mercedes service kit on eBay for £107, but will it cure the problem?

Cheers

After the engine has been stopped the 722.6 gearbox returns itself to 2nd gear by default (by design) it's the ETC controller that decides to change into 1st or remain in 2nd as the car starts off.

If the ETC controller detects a significant error it will turn its control of the transmission off, leaving the gearbox in whatever gear it is currently in and letting the pressures go up to "no electronic control" values. If you now stop the engine the ETC will regain control deciding on the previous error - if it has seen the same error three consecutive times it will brick itself and you will be stuck in 2nd gear with heavy clunks when you engage Drive or Reverse. If the ETC has only seen the error concerned less than three consecutive times (and all looks ok) it will revert to normal control behaviour.

From your descriptions looks like the ETC has scrammed once or twice but reverted to normal control, a few things can cause a scram, implausible input from its speed sensors, bad solenoid actuation, hydraulic valve problem, worn out friction rings, electrical wiring problem etc. Getting a fault code read (in your case, from your description, the ETC scramming will have recorded a fault code that came and went) by a garage may cost some money and also tends to hand you over to them for a possibly expensive solution so keep that in mind (that's part of the reason why some owners buy their own MB code readers).

You mention feeling 1st gear engagement as the car is coming to a stop, this is normal behaviour, the ETC controller will sequence down the gears to allow engine braking especially if you are coming to a stop downhill - that's assuming you stay in Drive (some people put the car into Neutral before the car stops). What's not normal is if any (ETC decided) gear changes feel very harsh changing down or conversely flared changing up.

A fault code reading would help your decision as to whether lower cost remedies such as replacing the conductor plate will fix the problem. Changing the ATF and filter is always a good idea but unlikely to be a remedy on its own to what you describe.