W203 C220 CDI keeps switching gears at 30mph when cold

[andy.alias]

My W203 C220 CDI keeps changing gears when I’m cruising at about 30mph and the car is cold (its been around -1 C overnight and 2/3 C in the day). I bought it recently and it’s got 150k on the clock, it’s had the gearbox oil and filter changed less than 10k ago.

When I say changes gears it’s like it can’t decide between 3rd and 4th. I’m wondering if it’s something like the oil level being incorrect or if it will need a new conductor plate. This car seems to change gear quicker and smoother than my previous w203 C220.

 

[alexanderfoti]

I have seen conductor plates do this, as the speed sensor signals become sporadic so it keeps changing gear.

Does it do the same thing if you engage cruise control on a level surface at 30mph?

 

[Doug1234]

My 97 w210 e300td started off doing this a few months before it became obvious it needed a new conductor plate.
Mine would go up and down between the gears same as yours ,keeping it pulling on throttle would keep it jumping back and forth until you backed of throttle and then it would change up ..ie you could play with it.
Eventually started going into limp with no dash warning and re starting got it going again until it had enough and left me with reverse and 2nd gear.
First noticable thing was it had rough 1-2 changes in slow rolling traffic, there was a 50 pence spring available from Mercedes dealers that fixed that problem with the one taken out being in four pieces.

 

[andy.alias]

Thanks for the info, it only seems to happen when it’s really cold, It hasn’t happened in a while now. I will try cruise control next time it happens. I’m probably going to change the plate myself but I will wait until it does if more often or worse.

 

[andy.alias]

I think I spoke too soon, it happened this morning but I didn’t have time to put cruise control on. It’s fine when it’s up to temp. Anyway it’s not a problem just yet, I should sort out the water in the drivers footwell problem really.

 

[andy.alias]

It only happens before it warms up, it does it even with cruise control set. I’ll keep monitoring it.

 

[Steve@Avantgarde]

I would say the TC lock up valve is jamming and its affecting the gearshift. If it gets better when its warm, then that is certainly the first place to start. The ultimate test would be to turn off the TC lock up valve with STAR and drive it when its cold.

 

[andy.alias]

I would say the TC lock up valve is jamming and its affecting the gearshift. If it gets better when its warm, then that is certainly the first place to start. The ultimate test would be to turn off the TC lock up valve with STAR and drive it when its cold.

TC as in Traction Control or Torque Convertor? Is it a physically accessible part?

 

[Steve@Avantgarde]

Torque converter.

You need to remove the valve body of the transmission

 

[andy.alias]

Torque converter.

You need to remove the valve body of the transmission

Is that part on the valve body itself or further in the depths? I’m happy to replace the valve body myself when it gets more serious, the car has done 152,000 miles.

 

[andy.alias]

After googling this little find is quite helpful, it’s a diagram of the valve body that the conductor plate sits on and shows all the various valves around the edges.

https://d2q1ebiag300ih.cloudfront.n...0/Mercedes_722.6_Interactive.pdf?v=1488909158

So I wonder if I can get a replacement valve or maybe just take it apart and clean it.

https://www.sonnax.com/tech_resources/600-mercedes-722-6-valve-body-layout

 

[andy.alias]

After reading another thread about this problem I’ve decided to try two tubes of Dr Trannys Shudder Fixx, i will get back with results.

 

[andy.alias]

150 miles in and it seems it’s doing something, some days I don’t notice it and other days it seems to be worse. I’ve read others say it works quite quickly and others say 2500-3000 miles. I will update with any changes