Slightly nagging Transmission problem 5G-Tronic 722.6 Five Speed Automatic Transmission

[rich.g.williams]

For a while there has been a problem engaging Drive (First gear) from Neutral. Sometimes there can be quite a jolt when Drive is engaged. There is no discernible pattern except that this happens after a run when the engine and transmission are hot (never when the car is cold). Everything else about the transmission seems normal.

The car is my early 2003 C200 Kompressor Coupe (CL203). The transmission is the 330Nm version of the 722.6, the car has done 45K miles. I have worked on these transmissions before without much success but I have a basic understanding of how they work and have read up quite a lot about them, I'm attaching a diagram that may be useful to others.

Any ideas about what might be the cause of this random jolting from Neutral to 1st gear would be much appreciated. PS if I put the transmission on the W setting rather than the S setting it still can jolt.

 

[mattkh]

the car has done 45K miles.
Any idea if the transmission fluid has been changed yet.

 

[ajlsl600]

Whist not being up to speed on merc tranies I think this sounds like shift solenoid clutch fill time being out of sync (loss of memory) I wud think this can be recalibrated or tc lock up issue,?

 

[Wighty]

What about just changing the gearbox electrical connection , fluid and filter as a cheapish start point .

 

[rich.g.williams]

the car has done 45K miles.
Any idea if the transmission fluid has been changed yet.

Only had the car since last June, there is a lot of service history and all looks good. Its quite likely that the transmission fluid has been changed. The 45K mileage is 100% genuine according to the MOT history.

Seems unlikely that the transmission fluid could cause the issue described because its too intermittent and happens when hot not cold.

 

[rich.g.williams]

Whist not being up to speed on merc tranies I think this sounds like shift solenoid clutch fill time being out of sync (loss of memory) I wud think this can be recalibrated or tc lock up issue,?

Seems unlikely that issue is caused by the ETC loosing memory (being out of sync). For that to be the problem the ETC would have to work out new clutch fill times very quickly every time it lost its memory. Not ruling that and ETC problems out though.

Yes problem with the TC Lock Up, that could be it but no feeling of TC problems while driving. Wonder if there's a simple way to check for the TC being the problem.

According to WIZ the B2 brake rings are responsible for a gentle engagement from Neutral to Drive 1st Gear.

 

[ajlsl600]

Makes sense. I understand there is electro solenoid on tc somewhere for lock up?
which solenoid valve is responsible for 1st gear speed?

 

[rich.g.williams]

What about just changing the gearbox electrical connection , fluid and filter as a cheapish start point .

Its possible to change the Conductor Plate and that would replace the male pins part of the connector. Changing the plastic connector shell might stop a leak but that's about all. Hydraulic fluid inside the ETC would definitely cause lots of problems but inside the connector or wiring loom - that's unlikely. All the signals on the connector are very low impedance and are exposed to transmission fluid inside the transmission anyway. A bad female pin in the wiring loom part of the connector would cause problems in other gears (the 1-2 solenoid is used for 5-4 shifts too) and the ETC would sense it and quite likely go into limp home 2nd Gear mode. That has never happened.

Very helpful to have these comments because I feel that I may miss the obvious simple explanation.

 

[malcolm E53 AMG]

In all probability it’s the speed sensor on the conductor plate (electric plate) are there any fault codes? I remember when my gearbox started playing up with the S210 and hard shifting into first and reverse was one of the symptoms ultimately expanding up with the gearbox locking in second gear

 

[rich.g.williams]

Makes sense. I understand there is electro solenoid on tc somewhere for lock up?
which solenoid valve is responsible for 1st gear speed?

There are six solenoids, three for shifts ( 1-2 2-3 3-4 and 1-2 is part of a 5-4 shift) one for shift pressure, one for modulating pressure, one for the TC lockup. There are two speed sensors, one thermistor for ATF temperature, one reed relay switch to prevent starter motor operation in Drive or Reverse. A sticking shift solenoid doesn't really fit the bill as being responsible for a gentle engagement from Neutral to Drive 1st Gear.

 

[rich.g.williams]

When in Neutral the shift situation is already established as first gear but the 3-4 shift solenoid is also held on to keep brake B2 empty (off). As the selector lever goes from N to D the 3-4 shift solenoid is turned off, the idea being to slowly fill brake B2 (B2a and B2b) and Drive is taken up.

 

[rich.g.williams]

Another diagram (edited out of WIZ) that may be useful to others.

 

[ajlsl600]

The op saying shift neut to 1st rough. I suspecting mod valve from neut to 1st is perhaps playing up.

 

[ajlsl600]

I wud imagine (not tried by me) that xentry would allow calibration and whilst maybe it won't improve situation it is a non invasive test of system??

 

[rich.g.williams]

An unusual quirk of the 722.6 is that 4th Gear is the "straight through" gear. That is engine RPM equals transmission output RPM (excluding any TC slip). Whereas 5th Gear is an overdrive gear where engine RPM is less than transmission output RPM (excluding any TC slip).

In 4th Gear everything inside the transmission is turning together (no wear?). In 5th Gear engine RPM is lower so less engine wear? So am I better of cruising in 4th Gear on long trips or cruising in 5th Gear on long trips?

 

[rich.g.williams]

The op saying shift neut to 1st rough. I suspecting mod valve from neut to 1st is perhaps playing up.

Yes thanks, a modulating pressure solenoid or valve problem that left modulating pressure too high would likely cause the sharp engagement from Neutral to Drive 1st Gear.

 

[ajlsl600]

Good luck to op there is indy on here who offers solenoid repair, replacement plus oil n filter change at a pretty reasonable cost. When remember who, where I may go to get my tranny oiln filter changed, now at 65 odd k miles

 

[rich.g.williams]

Good luck to op there is indy on here who offers solenoid repair, replacement plus oil n filter change at a pretty reasonable cost. When remember who, where I may go to get my tranny oiln filter changed, now at 65 odd k miles

Thank you very much.

I think it should also be possible to test both the shift pressure and modulating pressure solenoids on the bench in hot ATF. Its interesting that they work such that pressure is highest when the solenoid is off and minimum when solenoid is full on.

 

[ajlsl600]

I test trans where trans pump is 415psi but mod valves clutch pressures are 340, 375 Think that's to allow for internal leakages n wear n tear

 

[rich.g.williams]

I test trans where trans pump is 415psi but mod valves clutch pressures are 340, 375 Think that's to allow for internal leakages n wear n tear

There are at least four valves regulating various pressures. The main Working Pressure regulating valve vents pump pressure to sump to get Working Pressure which in turn is controlled by Modulating Pressure so a Modulating Pressure fault lets the Working Pressure go up.