Mercedes W208 CLK 200 Elegance gearbox problem ?

[CLKjohn78]

Hi everyone, This is my first time so please be patient !!
I,m desperate for some advice regarding an ongoing problem with my 1998 CLK200. Its only done 32000 miles and has always serviced properly by specialist garages using genuine Merc parts and quality oil .
I bought it 4 years ago with 13000 miles on the clock and its been brilliant up until now. Just before Christmas it started to clonk and jerk once presumably as the auto box changed down as you approached a junction. It didn't do it every time and sometimes it seemed as though the gear had not selected as you went to pull away. It then clunked as the drive took up. I was advised to replace the auto transmission oil with the geuine Mercedes transmission fluid also the filter. The old oil was clean as a whistle and apart from some minute carbon deposits in the filter there was no debris or swarf indicating any mechanical failures. The car now drives a lot smoother and the clunk/jerk has improved. I had the external transmission sensor with the "O" rings replaced with a new one even though it was not oil contaminated. The car was scanned, there were no suspicious fault codes that might indicate any gearbox problems. The MAF had recorded a fault in the past and the code was cleared, I was asked to drive the car for 200 miles or so we can see if the code returns and the MAF sensor needs replacing. Does anyone know if this is a MAF related problem or is it a gearbox problem? Its going back into be scanned on Thursday. As far as I know MAF is original and has never been replaced. I only use good petrol and the car is not modified in any way. Can you clean MAF sensors or shall I bite the bullet and replace it anyway. Thanks for taking the time to read this, sorry its gone on but I thought it better to include all the relevant information/symptoms.
Thanks , Regards CLkjohn78

 

[television]

I have copied this from the other post

Hello John, where does one start.

First the changes from cold can be hard, and the car will hang on to the first 2 gears to warm up the CAT quickly.

Regards the MAF, this can and does affect the engine output in terms of BHP output, If the MAF is going down, then if the engine output is down a touch, this can affect the shift points, so that the box may not be sure of what to do.

Welcome to the MB forum

 

[jberks]

If the MAF is original from 1998 it would be a fair candidate. I suspect 10 years from a MAF is a near record! My last one failed after 5 - though teh mileage will probably have been similar.
It may have deteriorated slowly so you haven't noticed but now, as Malcolm says, it's upsetting the gearbox - unusual but not impossble.
Drive it wellm, inclusing using kick downa fair bit, then see what codes are registered, though even if there are no recorded faults, I'd be tempted to get a new one from Bosch (Assuming it is a bosch one, it will be half the price of the dealer and is the same part). Don't touch Ebay ones!!

 

[CLKjohn78]

Thanks very much for your suggestions. I think it is a forgone conclusion for me to replace the MAF sensor. At least that way it eliminates it. It does drive a bit flat so it might perk it up a bit. I hardly get to drive it unless it needs fuel or there is a problem, the wife loves it and uses it far more than me. I will get a Bosch one. Its going to get scanned again tomorrow and I will replace it after it is done. Thanks to both of you for your advice. I wish I had known about this forum before. I am really impressed by the quality of the advice and the friendliness of the members.
Regards John

 

[CLKjohn78]

Ongoing problem !!

As I stated yesterday the car went into get scanned today (Thursday) we scanned it whilst it was not being driven and also did a live scan whilst it was. It all pointed to the MAF sensor it was showing very low voltage even when being driven hard under kickdown. We then live scanned an old C200 saloon with over 150 thousand miles on the clock to match the data readings of the MAF and its gearbox performance. Everything pointed to my MAF being defunct so we drove to the local Bosch spares shop and for just under £140 secured a new one. This was duly fitted and off I went. (There was no physical sign of any oil or other contamination on the sensor wire on the old MAF and the air filter housing is clean and dry with a very clean genuine filter fitted. ) The car is definitley more responsive and it drives much more crisply. However as soon as I slowed down for a left turn "Clunk" went the gearbox exactly the same. Having spent over £400 quid on it has anyone got any ideas what to try/replace next. I have just disconnected the battery and will leave it for three hours before re connecting to alleviate any stored glitches and allow the car to re learn / accept the new MAF. I,m guessing the only thing to do next is to replace the sensor plate deep in the bowels of the gearbox. My friendly specialist tells me they are about £150 plus about £100 labour.
He does about 4 of these a week on Mercs and they normally cause completly different faults to what I,m experiencing and show up as conclusive fault codes on the scan . He,s therefore reluctant to relace the sensor plate until it throws a proper wobbly and puts the car into limp home mode. Any ideas anyone ?????
Regards John

 

[Xtractorfan]

Did you have the gearbox error codes read and cancelled, it is worthwhile having this done before commiting to further work

 

[CLKjohn78]

Hi, yes he scanned and cleared them and to be doubly sure I disconnected the battery for over three hours and operated the lights a few times. Specialist Tech guy told me this will drain any residual charge in electrical backup system and clear all codes. Once I,ve run it with the new MAF and allowed it to adapt the ECU he's going to scan it again, fortunately he is a friend of a friend so he,s been very reasonable and also is interested in a proffesional way as this might assist him to diagnose similar problems. He does loads of Mercs and this one has got him puzzled !!
Regards John

 

[Arudge]

Did you resolve this issue at all? I have exactly the same, its got me puzzed as well. Many thanks. Andy.

 

[Steve@Avantgarde]

Best get fault codes read and the transmission oil level checked or the fluid and filter changed in the first instance.

It could also be an engine fault causing the gearbox to behave differently.

 

[Arudge]

We did have a lot of issues with the engine. We had a dead MAF killed by the copious amounts of oil in the induction system. We cleaned up the oil, cleaned out the crank vents and replaced the MAF.

Despite our work the car would, and without warning, drop dead without any response to the accelerator other than rampant backfiring. Error codes were mis fire related and supercharger related.

On occasion the battery warning light would illuminate despite a new battery and an alternator test, the cars overall drivability was poor.

Whilst looking for issues we had found low voltage at the battery post and power from the alternator appeared to ebb and flow, we traced the fault to a bad connection to the back of the alternator. Although all looked well the connector appeared to 'hit & mis', possibly as the engine moved back and forth.

With the connection repaired the engine burst into life and is now a pleasure to drive.

Low voltage has a lot to answer for.

At 104,000 miles we were unsure of the condition of the transmission fluid so it was changed. We used the 'flush through the banjo bolt' method as we had no torque converter drain.
The transmission was improved but we still had this clunk, just as the OP described, infuriating to say the least.

I haven't had the transmission codes read as yet.

I'd just been looking at the oil in TCU issue but i'm not sure mine suffers from this problem, there was certainly no oil leaking from the plug.

Shifting up is seamless, shifting down can be lumpy and the clunk can come from moving off the mark or shifting down to first, with a noticeable push forward when it does so. Its worst when it's cold but doesn't occur all the time.

The ATF had been changed before, the date stamp on the filter was 2013 but the dirty fluid we extracted appeared thicker than the approved fluid we put in, i'm beginning to think some idiot has used Dexron and maybe this is my issue, but of course, the OP had the same issue on a very low milage car.

Any ideas?

Many thanks, Andy.

 

[Arudge]

I've inspected the TCU and all is well. I pulled the board from it's case and it was bone dry.

For something to do i decided to test the ground points, ground points always seem to suffer as the years roll on and can cause havoc with electrics, as we all know.

With the clamp firmly on the negative battery post, engine running, lights on with all other electrical loads we test the grounds points.

The battery strap was good showing just 10mv, the main ground behind the binnacle was no more, neither was the ground forward of the fuse box. But the ground point for the engine strap was poor, 180mv, the other end of the strap was 290mv. Clearly, the engine to chassis ground strap is buggered and the chassis point needs investigating. There's a smaller ground strap running from the A/C compressor to the chassis which wasn't much better, there both on order.

If the gearbox needs to earth through the chassis we could be in trouble. The wiring diagrams in WIS don't seem to indicate any points going to ground but i find the WIS hard work, i'm hoping somebody with a greater understanding may chime in.

 

[Arudge]

Searching around i have found reference to what the OP and myself have experienced, it's known as bump shifting.

Bump shifting, along with flair shifting usually occurs in higher mileage units, somewhere around 180-200,000 miles. It's when hydraulic pressure is lost within the valve body due to wear. The wear occurs within the valve body due to actuators moving back and forth, pressure retained by the actuator leaks out. When the pressure is needed, and is not present, the transmission snatches, or bumps.

By virtue that there are repairs kits available on Ebay suggests the problem is a little more common than people think.

It's also reasonable to assume that when purchasing such a high quality car that you expect everything to be just so when new. I have worked in automotive manufacture for 35 years and can attest from my own experience this is not always the case. CNC machined parts are not always perfect, not every part is checked and bad parts do slip through.

When i can remove my valve body i'll check it. If i can slip the CMM (Computer measuring machine) operator a coffee i'll probe the bores and check for wear, although i would not be surprised if they were a touch oversize, hence the premature failure. These things do happen, but at least it's repairable.

This may take some time as i do need the car, but i will report back.

 

[Uncle Benz]

Not common by any stretch, but a broken spring in the valve body can cause erratic shifting in 722.6 transmission. I think I have only seen two in the last twenty years. Try googling 722.6 broken spring

 

[Arudge]

Not common by any stretch, but a broken spring in the valve body can cause erratic shifting in 722.6 transmission. I think I have only seen two in the last twenty years. Try googling 722.6 broken spring

I did stumble on the broken spring problem, but i understand it only affects transmissions prior to 1999, mine being 2000, but i'll check it anyway.

Most of the videos i've watched are American where the 722.6 is widely used by Chrysler, as well as Dodge and Jeep. I'm certainly not trying to suggest that the 722.6 is unreliable, is isn't, it's widely used by drag racers due it's robustness but all components have a failure rate. For an after market parts supplier to offer a high quality non genuine repair kit is indicative of a possible design issue, nothing is ever perfect.

Whats puzzling me is we seem to have actuators running in soft bores, which i would have thought would have a limited service life anyway, or maybe its debris suspended in the oil that's abraded the bores?

Sonnax appears to be the company of choice for 722.6 spares, they have some useful resources and i'm currently working my way through their website.

I've never stripped an auto box before so i'm on a bit of a steep learning curve, i'd welcome any contribution.

 

[Arudge]

I received an E-mail of a post from uncle Benz that hasn't been posted here, although it clearly stated that it had, the wonders of technology.

In reply to Uncle Benz, it was the OP's CLK that was 1998, i chimed in to see if he had any success in resolving the issue, mines 2000 and i do appear to have hijacked his thread!

I've stumbled on a 722.6 repair manual. It's not an MB publication but very informative all the same, and essential bedtime reading for the technically minded. It can be found here..

http://ftp.hamsk.ru/auto/W210/AKPP Mercedes-Manual.pdf

It has detailed diagnosis of the things that tend to go wrong and the hydraulic functionality of the valve block.

I shall now go away and study the drawings.

 

[Arudge]

When looking through the drawings i came across this section drawing, i wanted to bring your attention to the elevated ATF level, shown here by the hatching.

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Its been mentioned may time how fickle the fluid level is, and i've never understood why.

Certainly, if the level is too low you will start drawing air, this will drop the oil pressure with subsequent loss of hydraulic function.

If the level is too high it will swamp the rotating parts, will subsequently foam up having been aerated, resulting in the same loss of pressure and function.

But here MB have rather cleverly kept the ATF away from the rotating parts, allowing the ATF to expand due to heat in an outer chamber, around the outside. This allowed the whole gearbox to have a much lower profile, no sump hanging low under the car to clout the speed bumps and kept the ATF away from the rotating parts, very clever.

I fail to understand why being a touch over on the fluid level can do any harm, i'd have thought being too low at cold would do more damage, maybe somebody could chime in and explain. As it is, i don't think fluid level is anywhere near as important as it's being suggested, i'm certainly not going to agonise over a few mm of error.

 

[Arudge]

Within the Sonnax website is this handy cut out and keep chart, detailing the workings of the valveblock. It shows you what valve does what and what your likely to experience if a valve is not functioning correctly, more to the point is that the valve is worn and is leaking too much.

 

[Arudge]

Also within its pages are detailed test procedures. They test each valve assembly with a small vacuum pump. If the valve can hold 25" of mercury then then it's considered good. If it drop to 18" or less it's worn.

A worn valve will loose pressure, and affect the functionality of the circuit that it services, resulting in one or more of the symptoms that i, and others have experienced.

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[Arudge]

It was with some trepidation that i removed the valve block. But with reassurance from others that had done this before it proved easy enough. If anything, it was messy, the ATF gets everywhere, and continued to drip.
It's worth noting that the transmission does drain down. After draining the pan, removing the valve block, replacing the pan to keep things clean, after a week i'd collected a further 1.5l.

 

[Arudge]

This is the separator plate that separates the two valve block castings but allows oil to flow from one side to another to wherever it needs to go. The darker grey is a fine metallic deposit which needs to be cleaned, but something else is more apparent.
If you look closely most of the lines have a sharp definition to them, but some look smudged, evidence of blowby, oil being able to leak past where it shouldn't, this can't be good.