722.9 Auto Gearbox issue *Juddering*

[Allybassman]

Hi All,

Strange issue that my 2012 C Class (58k miles) has developed - Upon light load on the engine (keeping pace with traffic between 30-50 MPH I have started to feel the car judder. Accelarating is fine, the gearbox changes smoothly, doesn't hold onto gears too long and behaves normally.

It's when I get up to speed and lightly release my foot off the accelarator to feather it to keep my speed to the desired level is when the issue happens. The gearbox drops into a higher gear to reduce the revs as normal and once it's done that, if I press the throttle, after a few seconds it starts to judder and you can see the rev counter bouncing by a few hundred revs up and down. It's really noticeable if i'm going down hill and I press the throttle pedal lightly.

If I give it more throttle, the issue goes away, if the box changes down a gear the issue goes away too.

I've only owned the car a year - from the service history I can see that the gearbox fluid + filter was changed in March 2015 @ 18k miles. I'm wondering if it's telling me it needs a gearbox service or there is something more drastic wrong!

Thanks for reading

 

[Stratman]

40,000 miles on from a gearbox service it's worth at least checking the fluid level using the correct procedure.

The speeds you say it happens might hint at the lockup clutch, is this engaged with hydraulic pressure or is it electric?

 

[Allybassman]

Thanks for the reply,

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.

 

[Allybassman]

just returning to update this thread,

After weeks of every journey having this issue numerous times and being able to easily re-create it, the juderring suddenly went away / happened every so often.. typical as I had my car booked in with a reputable Mercedes specialist. I kept the appointment and took it down, they did a road test / scanned using STAR and found no faults (again, typical!) They advised that as the gearbox was due a service soon it would be a good idea to get it done now incase it's related to old fluid.

I got the car back and noticed straight away that the quality in shifts is much better, especailly 2-3 3-4 even when cold! I've not done a massive amount of miles since, so fingers crossed it's gone.

 

[Gazwould]

We have to remember that the 5 year / 77,500 interval is a maximum interval and whilst I don't do the mileage I fully intend to have mine done next year a year early.

 

[Petrol Pete]

IMHO I think getting the gearbox serviced is probably a better idea than crossing your fingers. Get the ECU transmission plug connector changed at the same time.

 

[Allybassman]

IMHO I think getting the gearbox serviced is probably a better idea than crossing your fingers. Get the ECU transmission plug connector changed at the same time.

Yes should have said in my post, I did get it serviced. They said that they personally recommend that the 7g gets serviced every 4 years/40k miles. My car was bang on 40k miles since the last change, so to me it was a no brainier to get it done while already on the ramps.

certainly is shifting better and no juddering has occurred in the usual scenarios. Early days though!

 

[Allybassman]

We have to remember that the 5 year / 77,500 interval is a maximum interval and whilst I don't do the mileage I fully intend to have mine done next year a year early.

A very sensible plan - my car is a keeper for the foreseeable, so my next change will be done in 4 years/40k miles for sure!

 

[Allybassman]

Just to update and close this thread,

After getting the Gearbox serviced, the issue went away...for a while. It returned and gradually got worse to the point that every journey was horrid. I booked the car in again with a specialist, but due to Covid-19 the wait for a slot was a few weeks.
While waiting I decided to perform a major service on the car as it was coming up to two years in my ownership. Upon remove the 'batwing' air intake I found a large hole in it on the underside and all the orange seals looked past their best..



I tried to repair the batwing intake, but in the end I ordered a brand new one to the tune of £700! Ouch.

New part fitted along with seals, air filter, fuel filter, cabin filter and oil change and I happy to say that issue has gone completely!

So it seems it was not gearbox related, but in fact an airleak causing rough running from the engine at low loads!