Jerky Transmission
 

I've spent a good amount of time searching and reading various threads about an issue that seems relatively common. I've got a 2003 CLK 500.

The issue I'm starting to notice is that from around 1,200 - 2,000 rpm you get a bit of lurching or "jerking" under light engine load. It is especially prevalent in the 20-40mph range. If you put a decent amount of engine load and don't allow the tranny to be in the 1,200 - 1,750 range in 3rd gear you don't get this behavior, but get a slightly rougher/slower upshift.

Occassionally, this can also be coupled with a grumble or rumbling from the rear of the car (sometimes even feeling vibrations). I have an appointment tuesday to check for glycol contamination and I am hoping for the best.

The real reason for making this post is that over the many threads I have read on this issue, it seems sometimes there is no glycol contamination. But what's more worrying, is that there have been many different diagnoses for the cause.

Some say valve body, clutch pack, conductor plate, torque converter, TCU replacement, TCU flash, fluid and filter flush or even a full transmission replacement. Is anyone fairly familiar with this particular issue and can offer a bit of advice/guidance? I'm hopeful my MB tech buddy at the dealer can accurately identify and fix the problem, but I'm scared what may end up happening is I change something that hides/masks the true problem and it will be a ticking time bomb; requiring total tranny repalcement (if I don't already need one... :(

Just to give an update to the situation (in case anyone also has the same issue and would like to know the resolution).

The culprit was in fact bad glycol contamination (well over 400):
Attachment 399757

My friend at the MB dealer has recommended replacement of the torque converter, friction packs, radiator (to behr), leaky adapter cable replacement and full tranny fluid flush. The grand total (if I did this through the dealer) would have been in the $5,000 range.

I was able to get this done for around $2,800 cash, which is a pretty good deal. But serves as a warning to RUN and not walk away from cars with the Valeo radiator.

This car did not exhibit any issues on test drive (which I specifically drove to try to find these issues). It seemed on the ride home when I drove it much harder the car began to act up.

I was okay taking the risk on this car as it is in otherwise perfect, pristine condition. I was also able to pre-negotiate an additional $1,000 off the purchase price of the car if the car did need work related to the radiator.

All in, I'm into the car for $12,500. I just hope that there will be no further damage out of this, as contamination was pretty bad - hopefully the tranny itself will be okay. Will know if it is resolved based on how it drives when I get it back (should be next weekend).

That sucks to hear but at least you got the issue resolved. The first thing I did when I got my 04 clk500 was changing out the valeo radiator. Then it was the transmission service. Very glad I got these things taken care of.

If this was my car I would fit a new Behr radiator & do a full flush fluid & filter change only & see how it goes. Glycol contamination does not necessarily ruin the transmission. The 722.6 is a tough old beast.

^ +1 It's not like the glycol actually damages anything. It's just the wrong viscosity for the hydraulic system.

About a week now after the fix. Things are MUCH better but not perfect. There is no more jerking, but I do get the occasional grumble/rumble. I think this is due to the fact that the friction pads/pack/discs (not sure the term he used off the top of my head) usually get affected by the glycol contamination and he said MBZ does not make them anymore.

So I'm just going to drive this into the ground and if it gets any worse, look into trading the car in (unless I can find friction packs somewhere).

Otherwise, very happy with the car. Tons of power, great ride and tons of features. Now I'm going to look into a few mods (quad exhaust conversion, tints and possible some foglight/interior light LED retrofit.

I've also changed the 3rd tail light out since it was cracked. Very quick and easy to do ~ 20 mins if you have all the right tools (T10 Torx, 10MM socket wrench, fingers).

Drive it for a while. With a recharge of friction modifiers clutch packs can improve with some use. Also make sure your rear tranny mount, flex discs & centre propshaft bearing are OK.