Whining ML270 CDi - transmission, steering, something else?

[iscaboy]

sounds like either a pressure relief valve or aeration going through a hydraulic valve block, both will make a singing / whining noise.

if the symptoms go away when you drain the straight hydraulic fluid (PAS systems etc) and refill with ATF (anti foaming properties) then that's what it is.

it's a sign of a manufacturing or assembly defect, can be non progressive, eg it will do that for the next 20 years, or it can be progressive, and one day it blows a seal in the valve block or something.

all the above of course assume you have clean filters, clean fluid, correct levels, etc.
if your levels are wrong you'll get pump cavitation*** which will do the same thing

the whining is from the hydraulic pump type, gear pumps (eg dowty etc) as used in PAS pumps etc deliver a lot of small pulses of oil, and the frequency rises with pump rpm.

in a pukka hydraulic system this isn't desirable, so you fit a damper which is basically pressure chamber filled with nitrogen which the oil uses as an expansion chamber.. bye bye whine and pulsing.

*** you do NOT want pump cavitation, you are literally listening to your pump being slowly eroded.

 

[Number_Cruncher]

>>If I stop, put it in neutral, and then rev the engine - the whine isn't there. If I then put it back in D and pull away then it's back.

>>Topped up a while back, no noises since.

Topped up which? The PAS, or the gearbox?

 

[MERC'ED!]

I have the same Whine on a c220 cdi !

Checked the power steering fluid seems to be full Enough....

What else Could WE check?

 

[Bobby Dazzler]

Topped up which? The PAS, or the gearbox?

Power Steering Fluid.

I have the same Whine on a c220 cdi !

Checked the power steering fluid seems to be full Enough....

What else Could WE check?

Ours was just within range on the dipstick built into the cap, but was enough to make it whine. Whereabouts is your fluid level on the dipstick?

 

[MERC'ED!]

It was on the Top line, closest to the top of the bottle, (BUT this was when WARM, So will Double check NOW, AS its Cold!)

Thanks for your Advice!

 

[jhon herry]

You didn't say what happens when you turn the key 10-15 times, no starter?motor doesn't turn over? turns but won't start? These questions have a lot of different solutions,I presume that your battery is in good shape,If when you turn the key and the motor doesn't turn over,you have a problem with the starter or ignition switch as the power is not getting to where it should be straight off,the fact that you turn the key so many times indicates one of these two factors as it will eventually start,It stutters and then dies,A diesel motor will do this when the fuel drains from the pump back to the fuel tank which means that the system is not airtight as it should be.A petrol engine would mean that the feed pump is not working properly or a fuel filter is clogged up,I could go on and on but the thing is to look Basic and reason it out,You can IM me if need be,love to help you but need better details

 

[MERC'ED!]

Power Steering Fluid.



Ours was just within range on the dipstick built into the cap, but was enough to make it whine. Whereabouts is your fluid level on the dipstick?

Hi, I checked my Fluid & topped it up regardless, (As its not Low atall Now!)

BUT the whining is still there! done around 5 miles, & can only hear it when the radio is off & I am Listening out for it!

 

[Bobby Dazzler]

Doh. Not that then. One last thing before the expensive business of new pumps, diffs, etc: I wonder if there could be air trapped? Could try leaving the cap off, and turning full-lock to full-lock a few times to purge any air?

Sounds fair in theory, perhaps someone who knows a little more about the practice could suggest if that's a good - or more importantly - bad idea!!

 

[Number_Cruncher]

>>Doh. Not that then.

I know this isn't helpful, but, intellectually, I'm really glad to hear that. I couldn't see how it could possibly be the PAS - how could the PAS possibly know what gear you're in?

However, in a similar vein, is the fluid level in the gearbox correct?

 

[MERC'ED!]

I am Wondering!?!?

I can suggest, that when I go over a Speedbump, the Noise goes & comes again as Gravity returns!

It a sort of clicky sound when whining, sounds as if somethings Revolving at the same speed but depending on the speed, as in the noise does not really max out when I drive Fast or any faster then 30 mph the noise does'nt go any louder then it is at 30 mph!

Any correct way of checking the Gearbox fluid level?

& is there any sort of vacum system thats connected to the gearbox? As I do go into limpmode, BUT am looking at the Inlet port motor, flaps linkage as suspect...

When cold the car drives great!

 

[Bluehoncho]

Hi, I am having exactly the same noise/symptoms on my ml 270cdi '02. Again it commences during hard acceleration and whilst turning, doesn't need to be as much as 90 degrees even 30-40 degrees and like yours it doesn't go away once its started until i have switched off the engine and returned to it later. I am thinking of changing the gearbox oil and have been reading that it is essential to use the mercedes oil??
Did you manage to find a cure for this noise? I have thought about it being connected to the steering, but the oil is in between the high and low marks, so I wouldn't have thought this could effect it. Of note my resevoir is on the rear left whilst facing the vehicle, so just in front of the steering wheel.
Thanks Jules

Hi
Did you manage to get a solution as I am having the same symptoms. I have recently had my auto gearbox refurbished and that has made no difference (was not the reason I had gearbox done though) - the vehicle has done approx 94K miles. When I have been an a golf trip with 4 of us with clubs and overnight bags etc I did not hear it as much, could the additional weight be any clues to the problem. Any help would be appreciated.

 

[philml270]

Hi all
Very expensive sounding noise exactly as described on this forum, a quick read, top up of power steering fluid and voila!!! no noise... wonderful thank you

 

[panason1c]

Hi all
Very expensive sounding noise exactly as described on this forum, a quick read, top up of power steering fluid and voila!!! no noise... wonderful thank you

The concern now would be that you probably have a leak somewhere in the system, as normally they never need a 'top up', mine has never needed topping up in the 8 years i've owned it. Check the rack track rod boots for any sign of dampness due to the rack seals (within the boots) weeping oil.

 

[gtvlusso]

Hi, I have had this twice now - horrible noise that sounds like gearbox. Seems to occur on sharp turn - fade out, be okay when you next start it - then occur again on a sharp turn.....

It is the PAS fluid - I bought a small bottle of the official merc fluid (as it is damn expensive) - very occasionally, like every 6 to 12 months months it just needs a top up.

I was told that this is very common, the sound will occur even if the fluid is almost at the full level - any reducation in level however small causes the issue.

So, please don't go replacing expensive parts until you have topped the level up fully. The reservoir is under the right hand side engine cover (as you look at the engine front on).