Jerky transmission (but only 3rd and 4th gear)

[Kombalar]

First: English is not my first language so sorry about possible spelling errors (or wrong words used).

I just purchased my car: MB 2014 200 CDI OM651 with 7-speed automatic transmission

As the topic title says: All shifts go up and down perfectly and this jerkiness happens on the 3rd gear mostly. Also when I put the car in the manual mode. I drove uphill from different gears and no jerkiness with gear 2 (1000-2000 rpm) but in the middle of hill it switched to 3rd and I let the rpm go down and then suddenly accelerate, it becomes extremely jerky and bumpy between 1400-1900 rpm..

When I performed the same test with 2nd gear (same rpm) no jerkiness at all.

Maybe with 4th gear same thing, but not as much. It's harder to test. But on the road with 5th and 6th gear (higher speeds) I have no problem.

What is your prediction? Is the gearbox broken for good? According to service history the trans oils have been changed about 60.000 miles ago.

All gear changes are okay and all problems occur between 1400-1900 rpm. When there's more RPM, I have no issues at all. The problem is not jerky switching at all but when the _gear is on_ and I "stress" the car in this certain RMP range it starts.

I'll take the car to repair shop asap and they'll take the codes but couldn't arrange it before next Friday. So it feels quite bad with new car right now.

I'd be EXTREMELY grateful if you could answer. What does this sound to you? A gearbox failure?


Thanks
Timo from Finland

 

[alecmascot]

FYI
2008 CLS320 cdi Gearbox

 

[Kombalar]

Thanks. And yes, I made this transmission reset already.

Absolutely no difference at all.

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[alecmascot]

That's not what the post was about.
Check with MB to see if you are missing a gearbox controller firmware upgrade.

 

[Petrol Pete]

Gearbox service 60000Km ago ? If that service was carried out properly by a reputable company you should be OK...but The cheapest option is to have the gearbox serviced again making sure they do a full fluid change including all fluid from the torque converter and the cooling pipes, also insisting on a change of gearbox ECU plug (not expensive) just to be sure.

What is the KM on the car in total ?

 

[Kombalar]

Gearbox service 60000Km ago ? If that service was carried out properly by a reputable company you should be OK...but The cheapest option is to have the gearbox serviced again making sure they do a full fluid change including all fluid from the torque converter and the cooling pipes, also insisting on a change of gearbox ECU plug (not expensive) just to be sure.

What is the KM on the car in total ?

Yes it was carried out by a reputable company. And I'm going to change the oils asap anyway.

Lots of kilometers, it's an old taxi. 200.000 miles (320.000 kilometers). But I drove 560.000 with my last one and never had transmission problems.

It's weird that shifts go all butter smooth though. The problem arises when the locked gear (3rd) is on and it's not shifting up or down.

 

[Petrol Pete]

My car has the older 5G 722.6 gearbox but is very similar, maybe at that age you should do the service and replace the conductor plate at the same time ? None of these jobs are difficult or very expensive and usually fix any 'faults' with this gearbox . Remember this transmission has been around for a long time and has a very good worldwide reputation for being strong. I think (from memory) it is rated at over 1000Nm

 

[Kombalar]

Thanks Pete. Appreciated. That made me feel a bit better. I'm just an average guy (but a hardcore Merc enthusiast for life) who can't afford a new Mercedes and I've always bought these high mile (somewhat newer) cars to enjoy them. I've been lucky so far but now I was thinking that my luck has ran out.

Yeah I've always been under the impression that if the turbine or gearbox are going to "explode" soon, the shifts are getting problematic and/or there's going to be a lot of noise, smell or something like that. This transmission is shifting gears perfectly.

Do you think I can safely drive this car now (my job requires that) without experiencing catastrophical consequences until I can get it to transmission service (in two weeks or so)? Can that kind of jerkiness create further damage to the gearbox fast?

And no.... 60.000 miles (about 89-90.000 kilometers ago) was the last gearbox fluid change. It has to be done asap.

 

[Justintyme]

I'm not sure about the 7 speed transmission, but the 5 speed 722.6 transmission needs an oil change every 40'000 Miles.....and pound for pound, in terms of trans problem's,,,oil punches way above it'e weight. Too much, too little, to old...

 

[Kombalar]

Yes. I looked at the documents and the last oil change was made in 2016, and about 90.000 kilometers ago. That is about 55.900 miles. It has been negleted but not grossly so and only 3 1/2 years since the last one.

 

[Kombalar]

From another forum:

"Jerking when accelerating is not the transmission unless it does it when it shifts. I've had 2 cars have gears go out and even when they are going out, if it actually goes into gear everything always worked fine until the gear is toast. It's only getting into that messed up gear that you would ever feel anything different."

Can someone confirm this?

 

[grober]

If the problem doesn't lie with the gearbox you may be developing a problem with your VGT [ VARIABLE GEOMETRY TURBO] If the vanes get cruded up and stick or the boost controls have a problem you might get symptoms like this. Other possibility is loss of boost under certain conditions due to EGR problems. Get the fault codes read on a decent system preferably MB Star but don't confine them to the gearbox.
How to diagnose problems with VNT turbos

 

[Kombalar]

Thanks a lot. I didn't think about turbo at all.

Today it was freezing in Finland (-5 Celcius) and after cold start the car ran flawlessly until it started to get warm. Maybe this helps too?

I try to get it diagnosed as soon as possible.

Another note: The engine temperature is at the 78-80 Celcius (should be at 90 C) but that's most likely a faulty thermostat (which isn't a big deal). I doubt that has anything to do with it but I just thought I should mention it.

 

[Kombalar]

Error codes: Nothing

Best transmission expert in Helsinki area drove it. Verdict: 99% sure it's the KYB solenoid. Nothing wrong with the trans itself. He said this is one of the most bullet proof transmissions in ANY car and fatal irreversible transmission failures are very rare.

Not a big deal as the trans oils have to be changed anyway. KYB solenoid/valve (or whatever) isn't too expensive.

Thank you everyone for the tips. Much appreciated.

Trans will get the full service in Wednesday and Thursday I will report again.

This kind of threads can help a lot of people when they go to the Google results.

 

[Kombalar]

Let's confirm this if and when someone is looking for a diagnosis of the same problem.

Changing the KYB valve (and changing the trans oil) corrected the problem 100%. Turbine was okay. Now it goes butter smooth.

If I understood the mechanic correctly he said that you just keep driving with the broken KYB valve, it could break the turbine, but not destroy the box itself.

KYB doesn't show in the error codes when it's going out (and the stuttering starts) - but a gearbox expert will notice it during a test drive. After a gear shift, the tachometer often "jumps" up 100 rpm. This is precisely because of this faulty valve. If problems and "sliding" occurs when the actual _shifting_ happens, then it's usually the turbine.

Maybe this helps.

Big thanks everyone, again. This is an amazing car without a doubt. And it still looks like a brand new inside and outside, despite high mileage.

 

[grober]

Not sure what you mean by KYB valve? What does it do?

 

[Kombalar]

Not sure what you mean by KYB valve? What does it do?

I'm not an expert but I believe it's a solenoid / valve that controls the turbine lock inside the transmission. They said it's a typical issue with high mileage transmissions. Thankfully it's not an expensive part and easy to fix (when you exchange the oils).

This can be from another transmission (not the 7-speed version) but it probably looks a bit like this.

 

[grober]

OK got you -- KYB refers to the manufacturer of hydraulic solenoid valves. These are normally associated with the gearbox conductor plate and presumably this one controls the lockup of the torque convertor.