W124 driveline vibrations following engine mount swap.

Frobus150

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Some months ago I decided to replace the engine mounts of my 240,000 mile MANUAL gearbox 1994 S124 E300 Diesel because they hadn't been done for years. I used genuine Mercedes mounts bought online from Inchcape Mercedes Oxford. For the first 25-30 miles when started from cold I get driveline vibrations when backing off the accelerator in high gear from about 40mph and below, for example when slowing down for a junction. Once the car is thoroughly warmed through the vibrations pretty much disappear.

My indy suggested replacing the front rear subframe mounts, so I did. Whilst this eliminated the slight driveline shunt I had been experiencing for years and made the gearchange nicer it had no effect on the driveline vibrations. He's now advocating changing the rear diff. mounts, which doubtless are ripe for replacement, but this involves five hours' labour so I'm in two minds.

Given that the vibrations are not present when the car's warmed through, can anybody suggest where the cause might lie? The propshaft doughnuts are in good nick generally BTW.
 

television

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This just is not easy, you do have all the prop shaft components, but I do not think they could change from hot to cold, you do have the rear gearbox mount
 

Doug1234

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I would expect that for it to take 20 to 25 miles before any difference is felt is about the time it takes the actual mount to warm up /soak up engine heat ?.

I have a 1990 300d and there are quite a few options on engine mounts ie cheap versus expensive and the cheap appear to be solid whereas the expensive are classed as hydraulic in that they are oil filled.

Could your new mounts make the engine sit lower or higher and affect the gearbox end prop doughnut ? ,which if like mine is not completely solid but has cutouts and a change of angle introduces the out of balance vibration ?.

It may be the newer stiffer mounts let/make the gearbox mount sway about a bit more ,but I cannot get my head around it taking those amount of miles to calm down.

Your indy likes your wallet ,go steady :)
 

Alex Crow

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Not sure if you are saying the problem has only happened since changing the mounts?

If not, yes, on the manual W124 the rear diff mounting bushes in the subframe used to wear pretty badly.
 

television

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Five hours to do diff bushes :shock:

You will have to open a branch down the road under a different name and charge for 6 hours :D:D
 

WG M-B

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But seriously though. A specialist with half an idea about 124's knows this is pretty extortionate!
I won't brag but it takes way less than half that time
 

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But seriously though. A specialist with half an idea about 124's knows this is pretty extortionate!
I won't brag but it takes way less than half that time

Maybe he is brand new fresh out of mercedes and rather than charge 2½ hours at £110 per hour he charged 5 hours at £55 :D:D
 

kth286

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First question: was there much difference in height between new and old mounts ?

I guess there was.

If so, why did you not change the gearbox mount ?

If the fronts have sunk, why wouldn't the rear also have sunk (gearbox end) ?

My guess is that you have raised the engine but the gearbox end is still low, and therefore
out of alignment with driveline now.

I would change the gearbox mount with genuine as well.
 
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Frobus150

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Thanks for the replies everyone. The gearbox mount has been changed too. The problem was not present before with my old mounts. Yes, the engine is sitting higher so a general change in alignment could be an issue. There is a mild drumming sensation too when driving at 50 -60 mph say.

Don't whether I should defend my indy or not but he offered to replace the rear diff mounts, diff seals, ABS sensor seal and reseal the back plate for £300 plus parts. The seals are only being done because the diff's coming out, not because they are leaking excessively. Please let me know if this is too much!
 

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Wrong mounts, that I do not know but easily checked by measuring the gap all round the fan shroud to the fan blade tips, it should be the same all round
 

WDB124066

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Some thoughts..,

Propshaft bearing AND check for play in the splines, yours is high milage, high torque, splines hate that. Maybe they have changed angle very slightly with the new mounts they hate that too??

Was the propshaft taken off during this exercise and did it go back on in the same orientation.

Could it be something wrong with the engine until it warms up. New mounts are stiffer and transmit this better? Low compression, bad spray patterns??

Trans fluid looks ok?

Diff mounts are always nice to have together with engine mounts, subframe and link bushes. Gives you the best feeling when this stuff is replaced at the same time.

124's did have a driveline vibration problem, there was a mass damper that could be bolted to the rear subframe by the diff.
 

Pathfinder

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Any height difference should be eliminated by the CV joint, providing it is in good condition, so I would suggest that's ruled out?

Any diff backlash?
 

television

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The odd thing here is OK when hot
 

WDB124066

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Forgot to mention UJ's, they are long lasting but yours is high mileage...??
 

Pathfinder

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Forgot to mention UJ's, they are long lasting but yours is high mileage...??
That's what I meant to say, UJ, not CV joint. Back in my days we called them the hardy spicer !
 

WDB124066

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Well it could be CV joints in the driveshafts; wind the windows down and have someone standing outside the car with a good ear, after shifting from foward to reverse and giving it a little gas do the rear axels click on either side...?? ... or back into drive after giving it a little gas...?
 
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Drive shafts will only operate properly if aligned properly in at least one direction. You need to check the alignment of the gearbox to the propshaft both in the vertical and horizontal planes. One of these must be perfect, the other then doesn't matter. If they are both out of line, you will get vibration.
 

Pathfinder

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Something worn in the drive train. Got to be, has to be.
 

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