Geartronic Issue

[MattM]

Some of you may know I've been having some issues with my geartronic gearbox. I recently did an ATF flush which hasn't fixed the main issue I have. Living with the problem since having the car I think I've manage to narrow down when it occurs, all I need to know now is why.

I will do my best to explain the problem as it's quite hard to explain.

Whenever I de-accelerate, be it braking or removing my foot from the accelerator, when the revs move down to around 2,000RPM, it then drops down to idle RPM (just below 1,000RPM). Then, when I press the accelerator down to speed up the rev needle will move up until until I feel a clunk and I then start picking up speed. This issue only seems to occur when done in the same gear. Let me explain.

If I'm travelling in 5th gear and de-accelerate and the revs drop down to idle as above, then I accelerate again, if the gear is 5th again then it clunks in. However, if I slow down enough that it uses 4th when I accelerator again, it comes in smoothly.

To test this I switched to geartronic mode. Travelling at approximately 3,000RPM in 5th gear I begin to slow. At 2,000RPM the revs drop down to idle. If I accelerate again (and the gear selected is the same) it will clunk in. This occurs in all gears.

Test 2 - Travelling at approximately 3,000RPM in 5th gear I begin to slow. At 2,000RPM the revs drop down to idle. I select 4th, then 5th again, and accelerate, no clunking.

Test 3 - Travelling at approximately 3,000RPM in 5th gear I begin to slow. At 2,000RPM the revs drop down to idle. I select 4th and accelerate, no clunking.


So as you can see, it only occurs in the same gear. Test 2 is interesting, as all I'm doing is selecting 4th and 5th again, electronically, I never accelerate in between selecting.

Now I'm not sure if these are 2 separate issues or not. When de-accelerating, are the revs supposed to drop down to idle around at 2,000RPM? What is causing this issue? Thanks for taking the time to read. Any questions let me know. Thanks.

Note - I have the latest TCM software update.

Matt

[timbo_1975]

This is the auto-neutral function, which AFAIK can be disabled with the dealer scan tool.

[MattM]

This is the auto-neutral function, which AFAIK can be disabled with the dealer scan tool.

Could you provide a little more info? Is this the same as 'freewheel on deacceleration' which I've seen mentioned on here?

[MattM]

Spoken to a specialist and I've been told that the auto-neutral function is only really for stop start driving, not what I'm describing. They seem to think it's most likely a valve body.... great! Better start looking at selling.

[wegal]

id check its not the gear neutral issue first, should be easy to do any indi with the diagnostic stuff could tell you, when the car is dropping down to idle speed its assumes that you are in start stop traffic. The fact that it drops to idle would indicate its just dropped into neutral, mine ( geartronic) holds the revs down to idle at stop and i KNOW mine doesnt have the gear neutral software.

[mds]

You really dont seem to be having much luck with your box Matt?

I have never had or heard of the symptoms you describe so cant be of much help other than to advise trying a good Automatic transmission specialist who should be able to run diagnostics on the box (all electrics and pressure test) that should identify the problem.
The E55 I had is the only Automatic I have had a problem with in 40years of driving nothing but Auto's. The problem it had was hunting for gears at constant speed, 60 to 80mph it would change up and down between 4/5 the Merc Dealer kept telling me they could find nothing wrong. Express Gearboxes in Portsmouth took 30mins to identify the problem was solonoid related on their test rig it cost me £37 (that was 3 years ago) I got a print out including analysis of the ATF condition. Then back to Mercedes armed with the print out and a big stick, result fixed by Mercedes as a "Good Will Gesture"

You must have a good Auto Transmission specialist near MK, see what they can find out. At least you will know whether to fix it or sell it.
Dave

[v70torslanda]

I have heard of an S80 with similar Geartronic issues, false neutrals/hunting for gears etc.

As a last resort before the box was stripped and rebuilt the owner took it to Trevor Burgess Volvo in Hyde (0161 368 9911) where Rob downloaded a software upgarde via VIDA.

This re-wrote the gearbox map and cured the car.

IMHO this has to be worth a go before anyone parts with 1500 quid for a valve body or decides to ditch the car cos its 'unreliable'.

Dealer could obviously do this but I would recommend a switched on independent, they have a vested interest in keeping your car running whereas the dealers these days are all too willing to take a ££££load of money off you and then have the argument about why it didn't cure the probelm you brought it in for.