722.9 Auto Gearbox issue *Juddering*

[allybassman]

Hi all,

just to update this thread,

as the car is hardly being used due to the current COVID-19 pandemic, when I do drive it the shudder when the TC locks up is much worse. It used to only affect low speed 4-5 gear but it’s now happening while on the motorway and in 7th. When you hold a constant throttle position for 10 seconds or so the revs start jumping slightly causing the whole car to shudder indefinitely until I increase or decrease throttle input.

Instead of a Mercedes specialist, is it worth going to an Auto box specialist?

Cheers all,

Alasdair

 

[Jason63]

Here's an off the wall suggestion - what if it isn't the gearbox. If the engine runs badly under certain load conditions you may not feel it when the TC clutch isn't locked.

Is it a hard judder or surging? Surging in my mind is like a more gentle modulation of the power. Surging can be an EGR problem.

A hard judder could be worn friction plates in the torque converter lockup clutch. This sort of judder is sometimes described as being like driving over a cattle grid. Perhaps low oil pressure for the lockup clutch (sticky solenoid or worn oil pump).

If it's pointing towards the gearbox then I'd get it to a transmission specialist. These 7G boxes are pretty common these days and someone experienced might be able to nail the problem in one go.

 

[McDonald]

Alistair, Jason 63 made the point that you don't really know what's causing the issue. The obvious advice is take it to a Merc Specialist Indie. They know about Mercedes gearboxes & everything else Mercedes. A gearbox specialist can completely rebuild the gearbox for you, but if that wasn't the source of your troubles, you're back where you started but with less money.

 

[allybassman]

Good shout on the EGR, the engine does run well as at low gears, pulling away from junctions and hard accelaration it pulls fine and no issue. The reason I think it's gearbox related is my reading about auto boxes and how they work as made me pay close attention to TC lockup - this is when I get the shudder / judder. The best way I can desribe it is you know when you pop the car into park and the hadbrake is not on tight enough, so the car rolls back slightly to rest on the park pin in the gearbox? it's like that, the feels like it's rocking forward and backwards gently and gets slightly worse if I keep the throttle in the same position.

It's very strange.

 

[allybassman]

Alistair, Jason 63 made the point that you don't really know what's causing the issue. The obvious advice is take it to a Merc Specialist Indie. They know about Mercedes gearboxes & everything else Mercedes. A gearbox specialist can completely rebuild the gearbox for you, but if that wasn't the source of your troubles, you're back where you started but with less money.

Yes and he's very right - I just thought i'd put it out to the forum again incase someone comes across it now or in the future that may have or had a similar issue to myself. Back to the Mercedes Specialist is my next port of call.

Alasdair

 

[Jason63]

Good shout on the EGR, the engine does run well as at low gears, pulling away from junctions and hard accelaration it pulls fine and no issue. The reason I think it's gearbox related is my reading about auto boxes and how they work as made me pay close attention to TC lockup - this is when I get the shudder / judder. The best way I can desribe it is you know when you pop the car into park and the hadbrake is not on tight enough, so the car rolls back slightly to rest on the park pin in the gearbox? it's like that, the feels like it's rocking forward and backwards gently and gets slightly worse if I keep the throttle in the same position.

It's very strange.

That could be the EGR. The EGR is inactive under acceleration to give the best performance, once at steady cruise the EGR becomes active to keep the nitrogen dioxide emissions down. The EGR is a closed loop control system and if something is wrong can oscillate causing small but repeated power surges.

A faulty TC lockup clutch tends to judder under load - that's strong acceleration, not cruising.

However a well worn TC lockup clutch (or one with low oil pressure) can cause an oscillation in revs at a steady speed. You don't tend to feel it that much, it tends to show more on the rev counter. Here the clutch attempts to lock up but the ECU detects slip, it disengages and tries again, repeatedly. In my experience it'll do it more when the gearbox oil is colder and it'll tend to be worse on a slight upwards incline, initiated when the car decides to change into a higher gear under very gentle acceleration.

The worn TC may not generate any fault codes which is unhelpful.

I'm far more familiar with BMW diesels than MB but on a BMW you can disconnect the vacuum hose to the EGR (and plug it so you don't create a vacuum leak). By doing this the car will flag an emissions warning but it'll stop using the EGR. You can then see if the EGR is the source of the problem or not.

 

[Jason63]

It looks like your EGR is electronically controlled only. In that case I think it would throw a fault code if it had a problem. You could however unplug it and see how the car drives but it will definitely log a fault code that may need clearing using XEntry or some other code reader.

 

[allybassman]

Thanks Jason, very useful information and suggestions. When it went into the Merc Specialist previously with the issue, they scanned it using STAR and no fault codes were found. The suggestions then was to change the fluid as it was due. Looking back now that could have be pointing towards a poorly TC... although when I got the car back the issues was gone for a month or two.

Although your description of TC lockup clutch issues and oscillation in revs appears very similiar to my issues, I find it to be worse when on a steady decline, not inclines as the engine is under load.

All very odd! Anyway I digress, I'll book it back in with them for further diagnosis. Ideally I'd like to take the tech out for a drive to get them to experience the issue - I guess that will be a no go under the current COVID-19 Pandemic!

Alasdair

 

[bembo449]

I had a customer with a similar issue , was cured with fresh fluid, filter and 2 tubes of dr trannys trans shudder fix

 

[Jason63]

It is sounding more and more like the TC lockup clutch to me.

Fresh oil fixed my BMW for a few months. I'm sure some friction modifying additive would have bought me a little time too.

In the end I removed the TC and had it re-manufactured by a specialist and refitted it - the difference to the car was huge. The failure had been creeping up on me and it affected the performance and drive much more than I had realised.

Just to complicate matters I also had a partial blockage in my vacuum system (the BMW EGR is vacuum controlled but electronically monitored) and that caused some very similar surging symptoms to the TC failure.

 

[Funkyboy]

I had exactly the same issue light throttle and vibrations through car could feel it through drivers seat.
went out with a Mercedes tech to replicate it. As soon as it happened he pointed out my driving style. Car needed more throttle I'm very light footed on accelerator. Since then I've given it slightly more and no problem since.

 

[Funkyboy]

Thanks for the replies - I'm hoping it's not the TC but it well could be!

This morning it behaved better - it's more noticeable when the car is cool and only done a few miles - again only under very specific circumstances of low load + high gear so the RPM is around the 1.1-1.3k rpm. After 30 minutes or so it's hard to recreate the issue. My googling is pointing towards TC valve? Either way I'll get it booked in to a local Mercedes Specialist.

You need to give it more revs when calling for acceleration in high gear. The gear box will drop a gear or two to enable you to accelerate. Next time you feel the vibration while slightly accelerating see what gear your in on the display and give it slightly more so it drops from 7 to 6 for example. If you were driving a manual you wouldnt be able to pull away in a higher gear you would need to drop into a lower gear. If you give it slightly more revs and there's no vibration you know it was your driving style

 

[Jason63]

That's very interesting, you're essentially saying that even with an auto you can labour the engine. I've never heard of that before, and I'm kind of disappointed with the gearbox software if that is possible.

 

[Funkyboy]

That's very interesting, you're essentially saying that even with an auto you can labour the engine. I've never heard of that before, and I'm kind of disappointed with the gearbox software if that is possible.

The gearbox is very good but it will need revs. Try it and if the vibrations stop you know what it was. I had exactly the same situation was really spoiling the car for me. No issues since. Your car won't shoot forward if you give slightly more revs it will just drop a gear or two as it prepares to pick up speed

 

[allybassman]

I had exactly the same issue light throttle and vibrations through car could feel it through drivers seat.
went out with a Mercedes tech to replicate it. As soon as it happened he pointed out my driving style. Car needed more throttle I'm very light footed on accelerator. Since then I've given it slightly more and no problem since.

Interesting, did the whole car judder and pulsate forwards and backwards? I have read similar things in the past about autoboxes and how to drive them, this is my 2nd auto although my first was a DSG which is very different to a TC 'slushbox'

I don't think this is my issue, it's very specific to when the TC locks up when cruising. Giving it more throttle, the gearbox behaves normally, it's only when things 'calm down' and you reduce to cruising throttle, the gearbox changes up to lower a lower gear (this change is when the juddering/pulsing starts)

Something did pop into my mind, when I first got the car nearly two years ago, I was stuck in traffic and was on a slight hill. When the line of traffic started to move, I took my foot off the brake and applied some throttle and the car stalled... at the time I thought it was very odd to stall an auto! It's never done that since, but the issue crept up not long after then and has very, very steadily got worse.

 

[V6Matty]

You know you can engage the TC lockup clutch with STAR when on a test drive, and good Indy that knows STAR should have done that and seen the live data feed

 

[allybassman]

Update:

Car is booked in with a Mercedes Specialist, 2 week wait which is totally understandable due to current situation and backlog! It's no bother to me as myself and the Wife are both WFH and we have her car to use.

Anyway, I planned to give the C350 a hefty service (Oil + Filter, Air, Cabin and Fuel filter + Orangle Turbo seal)
Upon closer inspection of the 'batwing' I noticed there was a large hole in it! The corregated rubber has been damaged so it was no longer able to be seated in the plastic end that connects to the Air filter cartridge. The orange seals between the Air filter cartridges + batwing were also toast amd looked to have been fitted incorrectly at some point in the past. I doubt sucking in hot air from the engine bay and god knows what other junk would have been ideal for a OM642....

Also goes to show that 'Full Service History' does not necessarily mean some jobs were not performed by complete tools... It further proves my own personal view on servicing my own vehicle myself and give the difficult jobs to a good indie!

I've tried and tried to get it to re-seal, but the rubber is all out of shape... gutted.

I've just ordered a new batwing... ouch those things are exspensive!

 

[Wighty]

You might be able to eBay your old batwing and recoup some money

 

[allybassman]

You might be able to eBay your old batwing and recoup some money

good idea, it also might be worth just packaging up and keeping for spare. I know the MAF sensors can let go so would be a handy thing to have!

 

[Jason63]

I'm surprised that didn't generate a fault code. When it's fixed it would be interesting to see if it was contributing to your judder.