w210 gearbox acting funny...

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renault12ts

MB Club Veteran
Joined
Mar 5, 2009
Messages
16,671
Car
2005 W215 CL500.
...so, travelling at a steady 70 on the motorway in top gear, the 'box decides to change down to 4th. A tap to the right does not change up to top. qait a bit, try a couple of time =s and eventually it changes into top.

This happened a half dozen times on 30 mile stretch. It happened when descending a hill at 70 foot off the throttle.

What's going on?

Please help?
 
I dont want to worry you unnecessarily but that was the initial symptoms of my Dad's box failure.
Get the fluid checked and have a look for drips just to rule out ATF loss.
 
If the cruise is engaged and the ECU detects an overspeed condition it will change down a gear to engine brake the car.
 
ATF will be checked. This happened with the CC on and off.
 
Gearbox may be a red herring. Could be the engine is down on torque, possibly due to an airleak weakening the mixture, or a MAF sensor starting to fail.

Check the ATF level first as this is the usual first port of call for strange gearbox issues. You can also check the pipes from the gearbox to the ATF fluid cooler as these rust on the 210 and lead to pinholes with a resultant gentle leak of fluid.

It may be possible to run this engine with the MAF disconnected and then see if the problem goes away - certainly possible on the 300TD but I don't know about the CDI - other people may be able to advise on this?
 
Update: All's well...one of the rear tyres was down to 20lbs and more worn than the other. Has not happened since supplying and fitting new air.
 
Low air in the rear would cause this? that's interesting, mine seems to be hanging in 4th on the M/Way, and I have a bad allow on the rear passenger side that needs a top-up now and then (ie once a week).

How does it affect things do you mind me asking?
 

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