Gearbox slight 3rd->4th flare?

stevesey

Senior Member
Joined
Sep 7, 2007
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Location
Bristol
Your Mercedes
C240 Sport 98
I'm not sure if there is anything wrong here - but I have noticed it recently and it's bugging me.

If I accelerate steadily, so the box changes gears between 2000 and 2500rpm, the change from 3rd -> 4th is very slow and flares slightly. Initially the revs increase by 200-300rpm then after about 1 second the gear change happens. This is most noticable on the 3rd -> 4th change, but can also be seen to a lesser extent on the 4th -> 5th change (rev increase is barely noticeable).

This is not always noticeable - mainly seems to happen on the flat or downhill e.g. down a motorway sliproad when accellerating steadily to reach 70 at the bottom. If you accellerate more briskly - e.g. so gear changes happen at 3000rpm the changes happen instantly with no rev increase.

Gearbox changes smoothly all the time and the level is spot on the top line when dipped. Rpm increase seems very low for a "flaring" type fault - or is this the first sign?

One thing I did ponder was that when you accellerate slowly the Torque Convertor may have time to lock up, and the rpm rise is the torque convertor un-locking before the change, then change itself is quite slow as the controller knows you aren't giving it large amounts of throttle. Accellerate more briskly the Torque Convertor never locks and the gearbox controller also goes for faster changes.

Thoughts anyone.

P.S. Maf was changed in Jan - the ATF at 100K and recently a partial change at 135K (no difference to symptoms - was planning this anyway).
 

Xtractorfan

Senior Member
Joined
Nov 16, 2007
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Your Mercedes
S class
Would suggest you have it put on a star diagnostic which should show up any problems that you may have..
 

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