Hi all,

Thi is my first post to the group, so allow me to first say hello. I'm Mike from the UK, have owned an E320 estate for a year, and its been great.

Spring greetings to you all.

I have been busy rifling through your old posts in the last few weeks in the hope of finding an answer to the problem of vibration only under torque lockup on the 722.6 trans.

I have still not found the answer, but I have no codes reported from the TCU, and the car otherwise drives ok.

The vibration is an aweful sound, heard in all 3 lockup gears and the rev needle DOES seem to sit around the 1500rpm mark, as others have noticed.

I have also noticed that along a flat road, in cruise, at around 35-40 mph, the lock up slip is constantly changing, causing the rpm needle to fluctuate +/- 100rpm.

Most annoying.

It may be that I need a new TCU, but I'm very aware that you can't "try before you buy" and I do not want to spend out on something that might not help. Although other posts SEEM to point to this being the answer.

The other posts I've found relating to this problem seem to end prematurely, with no fix reported. That either means they gave up and sold the car, or they couldnt talk about the cost as it bought them to tears.

I would be most grateful to any kind soul offering wise words on this before I get my leg lifted by an MB dealer.

Thanks in advance, and best wishes,

Mike Freeman
UK

Are you sure it’s a lock up chatter and not shifts chatter.


The lock up strategy has three mode, closed/slip/ and open. What you notice could be slip mode; 100 rpm drop is not much. What you need to monitor is PWM SOLENOID VAVLE STATUS, Closed duty cycle is greater then 80%, Slip 10 to 80%, Open is O%

The TCM can be commanding a slip mode, engaged, disengaged. Also lock up is only applied in 3rd, 4th and 5th gear.

Drive the car at above 55MPH at a steady throttle, monitor torque converter duty cycle and slippage RPM, a fully lock up converter will show 80% or greater DC. Fully locked
Slippage should be a negative number -100.

Do you know if the transmission has an update valve body, conductor plate and up dated soft ware to the TCM.. If not at lest change the torque converter solenoid, conductor plate and install an updated pressure regulator spring,

At my dealer just last week, the tech that keeps my C320 humming was working on a C32 with this very problem. Howling and groaning noises from the torque converter when in the 3-4-5 lockup gears. The fault in that car was a fluid transfer in the trans cooler in the radiator and the contaminant is glycol in the transmission fluid which is fatal for the transmission. He said the problem was the Italian made radiators (can't recall the well known brand MB uses) and the car in question was getting a new transmission and a radiator. Warranty in this case and they have done more than a few.

MB uses a test kit for the trans fluid to determine the glycol level.

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Roger E.

Thanks for all your replies.

I'm certain that the lockup is causing this condition. The trans slips fine and the howling is only evident under light throttle load at full lockup.

If you accelerate from 0-60, this is never experienced.

When this condition is met, it feels like the car is driving over a cattle grid, its even slows it down marginally, requiring added throttle to avoid speed decay.

I *really* hope the radiator and the trans doesnt need changing, as thats just catastrophic. I'll drive the car in the river Dart if thats the only answer.

If the TCU needs changing, can anyone give any pointers on where it is? Also, if any UK members know of anyone who sells the part. I'm very aware than an updated firmware was released for the 722.6, does anyone know what I should be asking for?

Thanks again for your replies and time.

Kind regards,

Mike Freeman

If it were my car, before I spent any money on parts, I would pay a dealer to do a trans fluid glycol test. Just to rule out the worst news. Then, any other parts costs will look like beer money.

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Roger E.

Hi,

An update. Went to a trans specialist and had the fluid level checked and the condition reported on.

Everything checks out ok. No glycol (I asked), not even burnt. Must have had an easy life so far.

The vibrations have not been so bad after a while to warm up properly, although are still evident to a degree. It is for this reason I no longer want to change the TCU. Its an unreliable gamble to take.

Just a reminder : no codes have been present on the TCU.

Has anyone any other ideas?

Kind regards,

Mike Freeman

I know someone that has a 97 E320 that had the same exact problem. At around 40 mph, there is supposed to be around 60-100 rpm worth of slip. Instead, there was less than 30rpm of slip which at that road speed and engine torque around 1500rpm led to a vibration. The problem was that there was not enough slip to isolate the inherent vibration that is present under those conditions, an updated computer for the tranny solved the problem in that specific case.

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Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record