tj83

Hi,

Apologies if someone has asked this before but I could not find any relevant thread. My car has started giving a mild/faint thump 1-2sec after braking/stopping.

Recently had alot of work done including full service, brake pad and disc change, gear oil and gear filter change, engine and gear box mounts. Lower suspension arms and anti rollbar and links. All original mercedes parts.

Car drives perfectly but just this iritating nuisance of mild thump/jerk after stopping/breaking. Initially not frequent but now almost regular.

I have reset tyranny. Thump has reduced in frequency but still there. I am lost.......My garage cannot find any codes. On searching other forums people have mentioned gear oil and filter change, reset tranny which I have done.

Someone has mentioned could be conductor plate/valve body/solenoids/torque converter. Can anybody help if they had similar experience and what helped .,.

BOTUS

try it using the C / S button and see if its different ? its the change down into the gear it expects to pull away in (as the vehicle comes to a rest), as S uses 1st gear its rougher than using second u get when its in C

the main reason you feel nasty changes is the boxes aren't much cop

tj83

Thank you Botus. My old W221 had C/S/M but this one S350 bluetec has E/S/M. I am getting it in E (I presume is Economy/Comfort) I would try S mode and see.

I see your point that it's change down on stopping that causes it. Change up is perfectly smooth. Any other suggestion. I have also done change up and change down reset yesterday, gear selector reset, Tranny reset and torque reset but still got a very faint thump after stopping. Not sure if doing them together is not helpful and should be done in a specific order. May be the car needs a long journey. I would get back after doing it. If any other suggestions causing it please I would appreciate..as almost already spent 2K on above work..

BOTUS

if they reset the gearbox adaptions (fill rates on the solenoids) it can take 40 miles to calm down - but then all shifts should be rough
they change badly its standard - there's a reason every other car manufacturer buy gearboxes from people that know what they are doing - for example BMW 6 and 8 speed autoboxes boxes are made by ZF a company that know what they are doing

S. Madman

Do you mean for example you get off the highway, stop at a red light. You are sitting there for some seconds while waiting for the light to change, not releasing the brake pedal at all, then all of the sudden you feel a small jerk?

If so perfectly normal, torque converter is taking a break. It will re-engage when the brake is off or gas is applied.

tj83

Thank you for replying. Yes, but it's happening on slow speed stopping. Faint thump after 3 secs and was never the case for last 3 years. Any suggestions? Drive is normal, no issues at all otherwise.

BOTUS

they don't work like this....

the torque converter is filled and slightly pressurised with fluid by the pump to stop cavitation (damaging bubbles just like you don't want on your boat prop). And is always "operational" if the engine is running and there is fluid in the box...

by the late 1980's to aid efficiency a further refinement joined the party, with the creation of the torque converter "lock up clutch". This improves upon the TC's awful efficiency from its worst efficiency of 0% drive (sitting stationary at the traffic lights - to ensure the engine doesn't stall), and then on from its previous best of 98% efficient at cruising speed, where the TC lock up clutch can under light load "lock up" drive to provide a one to one direct drive. Making it 100% efficient. This often breaks on Mercedes TC's, and can cause stalling at low rpm, especially at cold start - and cause hard low speed shifts as you are getting drive when you want 100% slip.. There is an adaption setting for this, but if its playing up its likely worn out and the box has to come out for a TC replacement or rebuild.



.

S. Madman

You are right, it never fully disengages. It does slip the lock up clutch, right? Another suggestion made in another forum is that the trans is going into neutral. To the TS, if you have paddle shifters do you feel another bump if you press the right shifter. If you don't try putting the car in drive again even if you screen is telling you are drive. See if you feel another bump.

tj83

Thanks for the advice. Would check and get back.

tj83

Sorry for late reply as wanted to drive 200 to 300 miles after transmission reset to update.

Faint thump still present but not as often in "E" mode.

No thump on stopping in "S" mode strangely.

Checked manual mode as well. No thump on stopping but gear changes felt a little jerky. It might just be normal as I never used the pedal shifters before so don't know what it feels like.

Not sure of the reason?

kevm14

My initial thought was the 2-1 which occurs at like 0.5 mph by the terrible update that I can't stand. But if it occurs in E (C?) which holds 2nd gear it's clearly something else.

BOTUS

I can't find the one about changing down delayed to reduce low speed poor change - but came across this on other forums...

What I don’t like is the “characteristic” of the transmission when I slow down, at 14km/h (8.69mph) it downshifts from 2-1. Every newer benz with these kind of transmissions continues in 2nd gear until you almost stop then engages 1st gear.

The main complaint was hard changes from 1 and 2 gears, this involves someone with STAR who knows the boxes to re adapt the torque converter lock up. I know that Colin at MBS is very good at this and I have been in two cars that he has set up and the changes were seamless and you never felt a thing.

and these old fixes for poor changes elsewhere
P-B-27.60/69 FEB06 Uncomfortable shifting quality 722.9 transmission; 3-2 or 4-3 downshift while decelerating may be the result of incorrect SCN coding; VIN ranges 221.171: A000355 – A016837.
P-B-27.60/69a JUL08 (VIN A000355 to A016837) S550 uncomfortable downshifting while coasting resolved by reprogramming the engine control module.