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

[rich.g.williams]

The rings you speak of are flat composite piston rings? Do they lock together or?

Rubber rectangular cross section O ring seals two per piston, one outside one inside. They sit in grooves.

 

[ajlsl600]

OK they are not slit with a lipped joint then?

 

[rich.g.williams]

OK they are not slit with a lipped joint then?

Some of the shafts inside the transmission have those "plastic metal" split seals but none inside the Torque Converter.

 

[ajlsl600]

Some of the shafts inside the transmission have those "plastic metal" split seals but none inside the Torque Converter.

They do wear flat and effect the sealind effect. Yr tc is a sealed, welded unit.? If so and you change it. Have old unit split on lathe, take a look inside, may learn something. Maybe there is someplace doing that, welding and balance.

 

[rich.g.williams]

They do wear flat and effect the sealind effect. Yr tc is a sealed, welded unit.? If so and you change it. Have old unit split on lathe, take a look inside, may learn something. Maybe there is someplace doing that, welding and balance.

Torque Converter Clutch Piston O rings will likely last a very long time. My post was about the small rubber O ring at the end of the transmission input shaft (that is fitted inside the Torque Converter).

Did you see the photos in my thread:-

722.6 Torque Converter (Part Number A2112500902) - Disassembly Photos


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[Vanlata203]

For now, the problem with the lock has stopped appearing every day, during the day let's say. For now I will drive so we will see if there will be a deepening of the problem.

 

[rich.g.williams]

For now, the problem with the lock has stopped appearing every day, during the day let's say. For now I will drive so we will see if there will be a deepening of the problem.

That's good news.

You may like to read this about the TCC, I don't agree with some of the material and the modifications but it's interesting.

Shudder Part 1

Shudder Part 2

Rumble Strip Noise RSN

There is a lot of info on so called RSN, on other forums. There is a modification to drill a small hole, effect of this is to drain to sump some of the TCC control pressure commanded by the TCC solenoid. I don't agree with making any modifications to the transmission but I see the idea, it's as if the TCC solenoid by design doesn't vent enough to sump when commanded off by the ETC.

There is a modification to open the TCC and fit a piston return spring, again I don't agree with this because the TCC working pressure will return the piston as soon as the TCC Lockup Clutch pressure drops. The TCC Lockup Clutch piston is controlled by the pressure differential between TCC working pressure and TCC Lockup Clutch pressure both inside the TCC.

Controlling the TCC Lockup is quite a daisy chain of events, something isn't happening as intended by the designers, it's just a matter of working out what.

TCC binding problems appear to cause a few different effects as follows:-

-RSN (rumble strip noise)
-bumpy engagement from N to D
-bumpy downshifts from 3rd to 2nd, 2nd to 1st
-lumpy feeling accelerating or climbing hill in lower gears

The W/S (C/S) selector W or C starts off in 2nd S starts off in 1st, better to use S if bumpy engagement is a problem.

 

[ajlsl600]

I wonder if any of above is incorporated in replacement pts from maker?

 

[rich.g.williams]

I wonder if any of above is incorporated in replacement pts from maker?

Nothing much of the above seems to have been taken up by MB. Sometimes they are talking about 722.6 transmissions fitted in the likes of Sprinter Vans, often transmissions that have done very high mileages and worked hard.

Sonnax seems to be the company that brings out many of the modification parts and modification kits and they market their philosophy heavily.

 

[rich.g.williams]

Took the car for a test drive this afternoon and was going perfectly until everything got well and truly hot. The torque converter seemed to have better range and gear shifts were good, however the old problem showed up again just as before. It showed up near the end of the journey after some time in slow moving traffic.

As for the cause of the fault I seem now to be left with electronics (speed sensors ETC etc), solenoids, electrical wiring, possibly the torque converter or something else.

I will investigate the electronics (the ETC) further to see if what the ETC is commanding is reasonable when the bump into Drive occurs, and to see if the speed sensor outputs are as they should be when the bump occurs. The fault only shows up when the ATF must be hot.

So although there were issues with the old ATF (and possibly the amount of it was low) the ATF was not the cause of the fault.

I do suspect the torque converter but it is hard to explain how the torque converter could behave so badly when ATF is hot and so well when ATF is cold or warm. A possible leaking O ring inside the torque converter seems unlikely to be leaking only when ATF is hot.

Back to my post number 55.

Having carefully studied how the Torque Converter Lockup works I have 99% convinced myself that the Torque Converter is not responsible for the bump when going from Neutral to Drive problem that my car has.

So today I disconnected (unplugged) the ETC and drove the car a short distance. As expected it starts and stays in 2nd gear. The TCC Solenoid must be off (TCC unlocked) and both the Mod pressure and Shift pressure solenoids both off so Mod pressure is maximum and Shift pressure is maximum. Sure enough the car starts off with a bump every time as Drive is engaged and its exactly the same bump as I have been experiencing previously. I know that the TCC is constantly unlocked because of how RPM changes while driving.

I'm thinking about Mod pressure again - does the ETC provide enough current to keep the Mod pressure solenoid on? Or does the Mod pressure solenoid get sticky?

Will investigate further - more tests.

 

[ajlsl600]

Just a thought. is mod press solenoid designed on, off only or should it be modulated take up by trans ecm

 

[rich.g.williams]

Just a thought. is mod press solenoid designed on, off only or should it be modulated take up by trans ecm

The ETC uses "Pulse Width Modulation" to vary the average current through the Mod solenoid (same for Shift pressure) trouble is that solenoids are not known for behaving well to varying currents and the control is open loop - there is no feedback to say that the Mod pressure desired by the ETC is the same as the actual pressure achieved. When the current is high the Mod solenoid is fully on and controls Mod pressure to drop to its lowest value (set by hydraulic regulator valve). Consequently Working pressure drops to its lowest value because the Working pressure regulator valve is controlled by Mod pressure. If the current through the Mod solenoid is zero (happens whenever the ETC sulks). The Mod pressure shoots up to its maximum value and consequentially Working pressure also shoots up to its maximum value (as per Working pressure regulator valve).

During my tests I never saw the ETC turn current to the Mod solenoid completely off (maybe it does when very fast shifts are required).

Will investigate further - more tests to record what the speed sensors and the Mod solenoid are doing when the bump occurs when controlled by the ETC.

I'm thinking that if a little extra current could be sneaked into the Mod Solenoid (lower Mod pressure) when the car is in Neutral the bump might not happen.

 

[ajlsl600]

The ETC uses "Pulse Width Modulation" to vary the average current through the Mod solenoid (same for Shift pressure) trouble is that solenoids are not known for behaving well to varying currents and the control is open loop - there is no feedback to say that the Mod pressure desired by the ETC is the same as the actual pressure achieved. When the current is high the Mod solenoid is fully on and controls Mod pressure to drop to its lowest value (set by hydraulic regulator valve). Consequently Working pressure drops to its lowest value because the Working pressure regulator valve is controlled by Mod pressure. If the current through the Mod solenoid is zero (happens whenever the ETC sulks). The Mod pressure shoots up to its maximum value and consequentially Working pressure also shoots up to its maximum value (as per Working pressure regulator valve).

During my tests I never saw the ETC turn current to the Mod solenoid completely off (maybe it does when very fast shifts are required).

Will investigate further - more tests to record what the speed sensors and the Mod solenoid are doing when the bump occurs when controlled by the ETC.

I'm thinking that if a little extra current could be sneaked into the Mod Solenoid (lower Mod pressure) when the car is in Neutral the bump might not happen.

I read urs. I not there but I think ur in right area now. In my experience fill times are tranny ecm controlled specifically to prevent sudden take up of load. I see no reason for that NOT To apply to tc lock up. There MAY be a reason. But I don't understand why, if there is one? . I continue to read with interest
I wonder the process thru star xentry for setting up a rebuilt/replaced tranny tc. And if that cud be the answer.
Previously I have had to kid the tranny ecm that the speed sensors or oil temp sensors are providing an in range signal to run thru the rebuilt tranny setup (earthmoving, not cars.) but it likely won't be to far different

 

[rich.g.williams]

I read urs. I not there but I think ur in right area now. In my experience fill times are tranny ecm controlled specifically to prevent sudden take up of load. I see no reason for that NOT To apply to tc lock up. There MAY be a reason. But I don't understand why, if there is one? . I continue to read with interest
I wonder the process thru star xentry for setting up a rebuilt/replaced tranny tc. And if that cud be the answer.
Previously I have had to kid the tranny ecm that the speed sensors or oil temp sensors are providing an in range signal to run thru the rebuilt tranny setup (earthmoving, not cars.) but it likely won't be to far different

I wish I had a Star Xentry system but suspect that I would get completely lost in all the adaptation and fill rate stuff. I understand what you say about kidding the transmission ETC that the speed sensors and oil temp sensor are providing an in range signal.

As regards TCC lockup I know that the TCC solenoid is off (unlocked) when in Neutral and when Drive is selected but if the Mod solenoid is left off (no ETC present) the bump occurs. So I'm thinking that the TCC cannot prevent that initial bump on its own, all it does is stall and by stalling it more than doubles engine torque, hence the bump. I'm pretty sure now that the bump is avoided by control of the B2 brake and by keeping Mod pressure at a minimum. The B2 brake is physically big and is complicated and is controlled by two separate pistons, also is controlled in part by the manual shift hydraulic selector valve.

Believe me if you wanted to get going in a hurry you wouldn't bother too much with Mod pressure - just let it mostly stay at maximum - shifts would be close to instant. That said, as you say prevention of sudden take up of load is desirable (even for earthmoving equipment?).

I get the feeling that there was quite a disconnect between the 722.6 hydraulic designer/designers and the electronic firmware designer/designers. The electronic firmware designer has done too much with PWM, adaptation and fill rates. That's my gut feeling lol. That said I would never criticise MB - good job the ETC is a Siemens product.

 

[Snake Charmer]

My understanding of the torque converter lockup clutch is to give direct drive and no slip under light loads effectively acting as a manual gearbox to increase efficiency and reduce losses. Once power is applied it should drop out seamlessly and allow slip.

 

[rich.g.williams]

My understanding of the torque converter lockup clutch is to give direct drive and no slip under light loads effectively acting as a manual gearbox to increase efficiency and reduce losses. Once power is applied it should drop out seamlessly and allow slip.

Its more involved than that.

As long as engine RPM are high enough the Lockup clutch locks to direct drive (in any gear). If power applied gets high the Lockup clutch has to allow some slipping and even fully unlock near maximum power.

As a driver I would want it to fully lock under light loads in 4th and 5th gear when road speed gets above about 35 mph, especially fully lock on the motorway (so that engine rpm stays as low as possible).

If the graph taken from WIZ is right its saying that the driver can control Lockup to some extent by accelerator Pedal Position.



Precis of info from wiz:-

Blades of the impeller spin ATF outwards to the turbine wheel causing it to rotate. The turbine wheel blades direct the oil onto the blades of the stator, which in turn push the oil back to the impeller. This diversion at the stator (which is supported against the transmission housing via the freewheel), produces an increase in torque. At the maximum speed difference between the impeller and turbine wheel the torque conversion achieves its maximum value of about times two.




The torque converter lockup clutch helps to reduce fuel consumption by reducing torque converter slip. This stands in contradiction to the ride comfort demands made on the drive train with regard to its vibration behavior. The task of the electronic transmission control is therefore to close the clutch in all driving situations relevant to fuel consumption, still ensuring that engine vibrations are isolated from the drive train.


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[Snake Charmer]

Great posts you are putting up.
Effectively light loads and engine braking by the graph. The clutch is too small for full power transfer. I use the engine braking on overrun quite a lot anticipating road conditions by selecting a lower gear to keep the rpm up above 1500rpm where the injectors are cut.

 

[rich.g.williams]

Great posts you are putting up.
Effectively light loads and engine braking by the graph. The clutch is too small for full power transfer. I use the engine braking on overrun quite a lot anticipating road conditions by selecting a lower gear to keep the rpm up above 1500rpm where the injectors are cut.

Thanks.

The clutch is not too small for full power transfer. For the A2112500902 Torque Converter there are two friction rings thicker and of a diameter as large as any clutch or brake rings in the transmission.

The problem is most likely things like "ride comfort demands made on the drive train with regard to its vibration behaviour" Also pushing maximum engine torque through the Lockup clutch alone likely creates vibration/harmonics in the drivetrain that are likely damaging to the engine/transmission/flexplate.

 

[ajlsl600]

Grand theory, however you are experiencing a fault of some kind that is not effecting many other running the same drive train, that being the case infers that the design itself is sound and that in Yr case there is an as yet unidentified issue..
Perhaps a tranny swap (borrow) and or tc is the answer to prove the point as to where the defect is , control of, or faulty part.

 

[charlysays]

I have plenty(not benz) experience of the friction plate v fine black powder like dust getting into the valves channels and and mod valves. One can get away with cleaning them for a while, but once in Yr always going to get some dramas, like a gear missing 4 a while
Only real solution is complete flush, change solenoid valves. Filter and oil. Plus repairs to what. Ever plates, brakes that are starting to or have broken up if you don't, at some point you will almost sure to be dealing with same issue again

I wonder if this is what went wrong with my old C250 TD gearbox. When cold it wouldn't go into 5th, then it even started not going into 4th.
I drained 700ml of fluid (changed only 5k before) and put in a bottle of lucas transmission fix and it did another 25k miles before showing any further issue. At that point I changed the fluid and filter again and mixed in another bottle of trans fix- it then ran another 15k miles until I crashed the car.