W210 E300 Turbodiesel Auto Gearbox Problem

[ticex]

My 2nd post in my 1st day on the forum!

I have another small problem with my Auto Gearbox. Whenever the car changes from 3rd gear into 2nd around town it does so with quite a "shunt". It is really evident if you have your foot down on the accelerator more but I've kind of adapted my driving to feather it when I sense the "bad" change coming. It's hard to describe but basically the car kind of lurches forward so it's rather annoying and I'm concerned it's doing damage somewhere.

It's a mystery to me and the dealers as in all other gears and speeds the box shifts ultra smooth. I was told by an independant mechanic a change of gearbox oil might cure it but the main dealer tells me not to bother as the box is sealed for life.

The car is a 1999 and has done about 45000 miles. Perhaps somebody else has had a similar problem or has some advice?

Thanks in advance!

Greetings,
Michael

 

[BillyBoy]

I'm only guessing off the top of my head here as I don't know a lot about Merc autos (despite driving one!) but I have driven various makes of auto box for the last 12 years. I believe box in question is fully electronic controlled by the engine management system (EMS). If so then some possibilities are:

1. A dodgy gear change solonoid. If the solonoid is sticking, it can cause a delay between when the EMS makes the change and when the brake bands actually engage. During this time, the EMS can start to re-apply the throttle causing a harsh change. Generally there is one solonoid per gear ratio (but not always) so this could back up your symptoms.

2. Dodgy or worn wiring loom. This could be either be on various sensors round the engine causing false signals to the EMS, or the connections on the gearbox causing the gear change solonoid to fire late (see point 1)

3. Dirty MAF sensor (if they're fitted on the diesel) - These can cause all sorts of wierd and apparently unrelated problems. I've certainly seen them cause harsh gear changes, but generally it tends to be over all ratios rather than one specific one, so this is probably less likely.


Points 1 and 2 should normally show up on a scan of the on board diagnostics computer but not always as it depends if the EMS can detect that something's wrong. Point three definately wont show up (unless the MAF has actually failed rather than being dirty).


Hope this helps, or at least gives some pointers.

Cheers,

Bill

 

[justin1820]

it is a fully electronic box if it has a w/s program selector switch by the gearstick, it has a control unit of its own named EGS which can be checked using suitable diagnostic equipment, if this shows no fault then a gearbox oil and filter change is a good idea but you do need a dipstick to check the level which is only available to the workshop, if none of these help then its time for a new gearbox and when this is fitted the gearbox control unit requires resetting so it addapts to the new gearbox

 

[wingco]

I have a W202 C250TD with the 5 speed auto box (722.6). I imagine the box is the same if not very similar.

Mine started with the faults you describe (3 to 4 change), and got worse and worse, until it would not change gear properly at all and was almost impossible to drive. It ended up having a new valve block and ECU which cost well over £1000 (paid for by signature warranty).

If you do not sort it out it will soon degenerate into a knackered box and cost you £1300 for a recon without labour.

All the MB specialists I have spoken to say change the ATF and filter, this sealed for life business is a load of rubbish.

I am going to get the ATF changed at regular intervals and I am told it will then be OK. Search the archives on this site as there is alot of information about the 722.6 gearbox and its problems.