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Revs rising on slow 3rd -> 4th changes

stevesey

MB Enthusiast
Joined
Sep 3, 2007
Messages
2,969
Location
Bristol
Car
Alfa 156 1.8TS
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 seems odd. 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.

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.

Is this normal? Anyone else noticed this? Gearbox changes smoothly all the time and the level is spot on the top line when dipped.

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.
 
I believe that it is known as "flare" when it does this; it is quite a common fault with MBs. I think that it can be repaired by replacing one or more valves - I even think that there are MB repair kits available. Check it out with an auto box specialist. How long since the ATF and filter was changed?
 
ATF done at 100K and I did a partial change the other week at 135K (made no difference, wasn't expecting it to, but I was planning on this anyway)

I thought "Flare" would be more aggressive - only goes up about 200rpm and dosen't feel like it's in neutral.

Any idea's how much a value replacements are (can be done from the sump pan).
 
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Mine does this occasionally (3rd to 4th).
Not yet done the ATF change, no idea about my MAF but the fuel consumption seems reasonably constant so no reason to suspect anything.

What are the valves mentioned? What to they do?
 
Hydraulic Values in the gearbox that control the changes.
 

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