Tranmission slip? Options?

[mazzarin]

Hi all, long time lurker here. In the past, I've found most of my answers by just searching but this time I couldn't find anything in particular. I have a 03 C320 4matic Sport (722.6 5AT). I love it to bits and have been taking it to an indy for service for a few years now. The primary tech was a BMW-trained technician and the shop dealt with all the germans/exotics so I felt OK taking it there. I didn't have a lot of options where I was. A few weeks ago, I started noticing some minor slippage going from 2nd->3rd, and occasionally on downshift 4th->3rd. It's a bit odd because depending on the speed (or maybe it's the revs?) I can get a smooth shift. It's never a hard jerk but it's quite annoying, like a newbie fumbling on a manual. The slip is maybe 1/4 sec though it is hard to measure. I took it to the tech and he said he didn't notice anything while driving it, but pointed out I was coming up to 100k (around 82k at the time) and that transmission should be flushed every 100k. He wouldn't do it in-shop (referred elsewhere) so I said we'll do it in a few weeks/months. In retrospect, after reading up here, I should have done it then. Since then, I've moved a bit away and the problem is still there and may have grown ever so slightly in intensity (or maybe I'm just noticing it more because I'm driving in more stop and go 20mph traffic on a 45mph road.) On occasion, if I'm entering a highway at slow speeds and go near-WOT, I might notice something a little 'off' on how it downshifts to rev up, but not a slip to the extent that happens at slow speeds (20-30mph.) That being said, the car has NEVER entered limp-home mode, it has not thrown any errors on the LCD (about the transmission / engine anyways) and generally works a charm besides that 3rd gear fumble. Is a full transmission flush the best course of action / think it'll resolve my issue? I'm really hoping that is it but after reading, reading, and reading some more, I'm starting to grow worried that I will need a rebuild.

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[Karo]

I have heard after a flush the tranny has been more smoother but not cure slipping.

Usually (hopefully someone can correct me on this) when a tranny starts slipping I don't think a flush will help at all.

Maybe more people can chime in but I don't think it's worth changing the tranny oil then if you do have a problem then taking it in to rebuild it (going to waste money).

Do you have any shops that focus more on transmissions? Maybe they can tell you what it is. But usually slipping isn't a good sign and like I said I highly doubt the flush will solve the problem.

[LILBENZ230]

Sounds like a Honda transmission.

I'm gonna side with Karo - I don't see how a flush will cure slippage.

[mazzarin]

Sorry for the delay. I took it to an indy to get it evaluated and he said it's not a slip; he would classify it more as a 'clunk' even though theres no audible sound.

He agreed with you guys in saying that if it's slipping, the flush won't do anything, but was less decisive after driving the car around and realizing it's not slipping.

Taking it to a MB club-recommended service center tomorrow morning and seeing what they have to say!

[Karo]

Originally Posted by mazzarin

Sorry for the delay. I took it to an indy to get it evaluated and he said it's not a slip; he would classify it more as a 'clunk' even though theres no audible sound.

He agreed with you guys in saying that if it's slipping, the flush won't do anything, but was less decisive after driving the car around and realizing it's not slipping.

Taking it to a MB club-recommended service center tomorrow morning and seeing what they have to say!

Good Luck, I hope it's not anything big.

[Emin]

Yeah, a flush can help the shifting smoothen, but once your slippin your slippin

[Glyn M Ruck]

Change & flush transmission fluid every 60,000 kilometres like the rest of the world - new filter etc. Then reflash the software & you will probably be OK. The only common failure on the 722.6 transmission is the one way clutch on 1st to 2nd change & at extreme mileage & usually in taxi service. If you have burnt a clutch then it's all over but unlikely. Does the fluid smell burnt? Clunk could be the torque converter clutches disengaging when they should not - reflash should fix. MAKE SURE YOU DON"T HAVE A LEAKING TCU PLUG O RING WHERE IT PLUGS INTO THE FRONT OF THE TRANSMISSION. TCU is in the passenger footwell under the foot plate. Make sure no oil has wicked up the harness. Look for oil under the carpet in the footwell. Oil must not get into the TCU or things can get expensive.

This transmission is not like a Honda - when they let go & slip they do it in grand style & are cooked.

[mazzarin]

Thanks for the input!

I didn't notice any oil under the carpet so I'm hoping for the best with that.

I took it to a MB service center who could not duplicate the issue (it may just be too subtle for them!) and informed me that the car wasn't throwing any codes. Oddly enough, I was (pretty much) throwing money at the SA and he was quite resistant to me getting a transmission flush. He stated to do it now is throwing money down the drain*. (However, it would be fine to get it flushed when I come in for 100k service.) I'm still very happy with my experience there.

The tech wasn't sure about resetting the software as you suggested so I told them alright, fine, we'll leave it for 11k more miles. I did perform a throttle-by-wire reset and it seems to have alleviated the issue quite a bit (though still not completely 100% smooth.) I suppose it was incorrect to say slippage in the first place.

I had another issue with some clunking due to shot front stabilizers, and I had those replaced. The car ride is much more enjoyable now. The combination of constant clunking over any imperfection in the road combined with slight 'offness' in shifting was driving me insane.

On that note: is it 'worth it' to get an extended warranty from Chrysler, etc.? Just in case? If only to cover through the 100k service and if the tranny needs it then so much the better...

[NLRL]

Check if the transmission oil radiator did not have a leak, contaminated your oil and is impacting the transmission.
I am going through a similar issue right now on a 2003 C230K.
It seems that in 2002 2004 MB installed some bad radiators-Valeo
Hop it helps