CLS55 diff issue

[Lenny63]

Hi everyone

So for a while now I have been experiencing a harsh "thud" from the rear of the car when I let off the accelerator if I am accelerating quickly- if I move into 1st or second gear and go on and off the pedal even at low speeds , the this is audible and also can be felt

I initially thought of possible diff mounts , or broken subframe bushes/bolts ...after taking to two local mercedes indies I have used before both were puzzled....o e went out on a limb and said he thought it could be diff related but wouldnt want to put his name against it incase I spent £££ and it didnt cure it (can you tell yet in Northern Ireland are merc indies are not very good )....

So last week I had the gearbox fluid changed , full serviced and diff oil service done at a garage I trust and they sort some time investigating this issue

- car was placed on a 4 post ramp, and they identified that when I move from neutral to reverse cycling through the gears with brakes on, the thud can be felt and heard even when stationary....they tracked it down to the rear diff...
- they believe it may be diff back lash ...but again they aren't 100% sure as they arent specialists in that field...

I have uploaded two videos for you...first one is manually rotating the proper shaft when car in neutral and you can see visibly there is play / excess rotation

The second video is the car cycling through the gears whilst on the ramp ..if you listen you can hear the clunk or thud very faintly as the proper shaft rotates as the car selects gear

Now i have thought about a new hit and its £2200 from mercedes and fitting

I've also thought about a quaife or wavetrac but I am unsure if this will cure ...it almost seems like the play is linked to the input shaft and the bearings that might be in there in the diff casing!!?? Again I am no expert

Any advice or help would be appreciated

Ps diff oil was also changed last Friday and no difference in behaviour

Video 1

To view this content we will need your consent to set third party cookies.
For more detailed information, see our cookies page.

Accept third party cookies

Video 2

To view this content we will need your consent to set third party cookies.
For more detailed information, see our cookies page.

Accept third party cookies

Regards

Lenny

 

[whitenemesis]

Crown gear thrust washer/bearing? Might be possible to adjust out any wear, or fit new?
Have you checked the condition of the gearbox mount?

 

[Lenny63]

@whitenemesis replaced last month mate and I thought it may well cure...however the thud is definitely isolated to the diff

I will look into the crown gear stuff you've mentioned above

Thanks

 

[topdown]

I had the same issue and it was the diff mounting bolts. Apparently they can stretch and should be replaced and torqued up,

 

[Lenny63]

Is that the 4 bolts that hold the diff onto the carrier ?

 

[topdown]

I think it was the cage to the subframe. The clunk is the cage banging on the subframe. You will not feel any movement by feel. The torque of the V8 power turns the diff and cage.

 

[topdown]

I think it was the cage to the subframe. The clunk is the cage banging on the subframe. You will not feel any movement by feel. The torque of the V8 power turns the diff and cage.

 

[Lenny63]

I don't think this is my issue
The noise is heard by hand moving the prop shaft

 

[Bellow]

You will hear backlash on any diff with your ear as close as that (ie, when you are underneath the car right next to it) and anyone who has selected Park then had the car move a few inches knows that backlash is a harmless reality.
A 'thud' is different. For the price of the bolts.... The diff breaking loose from its mountings is a horror story best avoided.
The torque reversal that those bolts are restraining is engine torque x first gear ratio x (TC multiplication if auto) x final drive ratio. Somewhere between 12 to 24 x engine torque.

 

[Lenny63]

@Bellow thanks for your reply

Do you mean the bolts that screw into the diff and then onto the diff mounting plate ...
Or do you mean the bolts that hold the diff mounting plate to the subframe (think these also have bushes?)
Thanks

 

[Bellow]

@Bellow thanks for your reply

Do you mean the bolts that screw into the diff and then onto the diff mounting plate ...
Or do you mean the bolts that hold the diff mounting plate to the subframe (think these also have bushes?)
Thanks

I'm not familiar with the arrangement but I'd be checking the whole lot including the bushes. Go in hard with a pinch bar. Look also for signs of the diff casing making contact with any part of the chassis and/or subframe. Under drive torque, the diff is trying to rotate around the axis of the axle shafts and push its nose upward.

 

[Jobsworth]

It's usually the diff front mount that goes first. It's a vertical bolt through the subframe with a big washer each side. The washer has rubber bonded to it if memory serves. The rubber disintegrates and allows metal to metal with some free play. Worth taking it apart for a look. Quick and easy to do.

 

[Lenny63]

Thanks @Jobsworth

That must be the mount that that screws up into the subframe

 

[Nat]

Any closer to getting it sorted out Lenny?

 

[Lenny63]

Unfortunately not mate ...wont get a chance to have to looked it again until next weekend probably ...I only use the car once a week if even at the moment and it's for leisure travel so as much as I'd like to get sorted its fallen down the priority list