if i let go of the throttle and then push down i get knocking/bang from rear

[SilverSaloon]

hi

on my 1994 E300D W124, when i am driving along, if i take my foot completely off the accelerator and then push it down quickly, say to about half way, i get a bang/knock that appears to come from the back of the car.

any ideas what this could be and how to fix it? its fine to drive normally and not really that bad, but its just a bit annoying if its something i can fix quite easily.

i assume its some mounts that need replacing.... maybe something with the diff?

i used to have a similar issue on a previous car which turned out to be an engine support mount but it appears to be coming from the rear rather than the front.

thanks

Derek

 

[wemorgan]

I'd also check the exhaust hangers. As the engine twists it loads up the hangers, especially the last one.

 

[Druk]

^ What he said. The bend just before the back silencer is close to the fueltank N/S and it can touch. The later cars also had two silentbloc type bushes in the diff mount which were prone to failure. (iirc...it's been a while )

 

[Olivier]

Hi Dereck,
Have you looked at the rear sub-frame bushes?
Olivier

 

[Ade B]

+1 for exhaust hangers first check - they have odd affects and are easier than engine/gearbox/diff mounts to get at afaik..

My recently replaced centre and back sections have almost eliminated the stationary in D grinding noise which I was getting, which was presumably caused by the engine twisting the exhaust against the bodywork near the transmission tunnel...

When the rear subframe bushes on mine were shot, the car felt distinctly more wallowy than usual, it almost felt like it was crabbing slightly on the motorway..

Hope you track it down.

Ade

 

[SilverSaloon]

thanks. i should of also said i can feel the knock aswell quite easily through the car, rather than just hear a noise, but will check the exhaust hangers. i just changed one front metal "strap" as it had corrodded and was causing a rattle, so maybe the others mounts are on their way out.

incidently i also feel the same knock when the car changes gear from 1 to 2 or maybe 2 to 3 just as i take my foot off the accelerator (ie when in a slow traffic queue).

the car feels quite tight etc to drive.

cheers

derek

 

[BlackC55]

Subframe bushes!!!

 

[Sp!ke]

It'll be the play in the diff.

Annoying I agree but it'll likely carry on just fine like that for another 100,000+ miles.

 

[SilverSaloon]

Subframe bushes!!!

easy to replace on a W124 estate? do you know of a howto anywhere?

 

[EDZ649]

+1 for the sub-frame bushes, got a similar problem on my 129.

 

[BlackC55]

easy to replace on a W124 estate? do you know of a howto anywhere?

They are not easy to do but easy enough.

Check them first though.

I very much doubt a diff issue.

 

[SilverSaloon]

They are not easy to do but easy enough.

Check them first though.

I very much doubt a diff issue.

this isnt a new issue, been like it for past 10,000 at least, i just never really bothered about it.

how do you check them? is there anything obvious i can check for?

 

[Sp!ke]

On mine, it is most definately the diff.

Quite common on manual gearbox mercs apparently.

 

[Olivier]

bad front rear-frame bush.
Diy:
DIY: Rear Axle Carrier Mount (Rear Subframe Mount) Replacement - Benzworld.org - Mercedes-Benz Discussion Forum

 

[BlackC55]

this isnt a new issue, been like it for past 10,000 at least, i just never really bothered about it.

how do you check them? is there anything obvious i can check for?

See if they are split. It is as simple as that.

 

[verysideways]

Sounds like diff mounts or subframe bushes to me... but could be exhaust too.

 

[SilverSaloon]

thanks - i'll take a good look at the weekend.

its an auto by the way

 

[verysideways]

If it was subframe i'd expect it to happen on bumps as well - ditto exhaust.
So i'm leaning towards diff mounts...

 

[kth286]

If it was subframe i'd expect it to happen on bumps as well - ditto exhaust.
So i'm leaning towards diff mounts...

diff mounts.

twisting action causes the left hand mount (looking under rear of car) to wear.

you will likely see internal section elongated compared to to other mount.

the diff can bang against underside of car floor.

it needs doing because the front seal (prop) will ovalise and leak with constant movement.

 

[SilverSaloon]

Just a little update to this thread. Its definatly the subframe mounts (or atleast they are definatly worn). They look like Olivier's pic above.... both sides.