SL 500 - Strange whirring noise when decelerating

[jfdi]

I have had a SL 500 (1999, 77,000 miles) for a few months and a couple of days ago it developed (suddenly) a strange whirring noise when I lift off the accelerator.

It sounds loudest near the auto gearbox, sounds a bit like a bearing noise, and goes away as soon as the accelerator is touched. It's louder when the engine is cold but never really goes away. The pitch of the sound doesn't seem related to speed.

I think the noise may also occur when going backwards, but I haven't had the opportunity to reverse long enough and fast enough to be sure.

The noise appears whether or not the brake pedal is pressed.

Thanks in advance for any ideas!
Regards
JFDI

 

[television]

This is an odd one,,same engine as in my SL, there is nothing beyond the gear box that could make any sound

 

[Xtractorfan]

Quite a few possibilities, the one that comes to mind is the pinion bearing in the back axle.. also could be something caught around the drive shaft..does yours have a centre bearing on the driveshaft, another possibility

 

[television]

Quite a few possibilities, the one that comes to mind is the pinion bearing in the back axle.. also could be something caught around the drive shaft..does yours have a centre bearing on the driveshaft, another possibility

Have to agree with the diff,, I read it as the noise was there when stationery. But when driving at say 40 -50 mph and you take you foot off, then the humming starts.
We had a 129 a few weeks back with the same whining diff bearing

 

[jfdi]

Thanks for your quick responses!
It could be the diff, but it certainly doesn't sound like any diff noise I've heard before.

The noise is not there when stationary, is most noticeable at, say 10 to 20 mph. It's still there at 40 to 50mph, but less noticeable.

One interesting point - I first noticed the noise after I had a lot of trouble escaping from a snowed and iced up car park. During this there was a lot of slipping of one wheel at a time, so could this have damaged the diff?

Thanks again
JFDI

 

[television]

Do check the oil level, and quite possible the spinning wheel started it off, though the pinion bearing is on the propshaft end of the diff. there are a few specialist repairers that can fix it, some use additives to quieten them down

 

[jfdi]

Thanks Television
I guess you mean the diff oil level? Presumably the normal oil level is up to the filler on the diff casing. What spec oil is required?

Finally - any ideas on how I might further implicate (or eliminate) the pinion bearing?

Rgds
JFDI

 

[television]

You fill it to the level of the filler 30 in the link, do make sure that the vent 300 is clean and clear.
I will try and find the oil grade

http://www.detali.ru/cat/oem_mb2.as...GA=722.624&CT=F&cat=44F&SID=35&SGR=015&SGN=01

Any good engineer could replace the bearings,, I used to do it myself

 

[jfdi]

Thanks again Television
Is there any way I can implicate the pinion bearing without going ahead and replacing it?
Or...
Would the problem bearings be in the diff itself?

I guess the noise could definitely to sound as if it's coming from the auto selector.

The strange bit (to me) is the way the sound is only present on lift off the accelerator - under even the slightest acceleration the noise disappears.

Thx again
JFDI

 

[television]

Thanks again Television
Is there any way I can implicate the pinion bearing without going ahead and replacing it?
Or...
Would the problem bearings be in the diff itself?

I guess the noise could definitely to sound as if it's coming from the auto selector.

The strange bit (to me) is the way the sound is only present on lift off the accelerator - under even the slightest acceleration the noise disappears.

Thx again
JFDI

Lapping in gears is something that I learnt to do when 15 years old.

With gears the two mating faces must only touch in the center of the teeth, if one gear is running out of mesh that would mean that one gear wheel is running on the edge of the teeth, and is this that makes the whine.

With the car diff and the pinion bearing goes, the gears are kept in mesh by the trust from the engine, when you take your foot off the throttle, this forces the pinion to tip, due to the bearing that has failed , and as it out of mesh it sings away.

 

[tjoneill@btconnect.com]

hi, in my experience, when pinion bearings are
worn they are noisy all the time not just under deacceleration,
can I suggest prop centre mount has collapsed as prop drops down
under deacceleration and lifts its self back up under the load of acceleration,
its quite awkward to check even on a ramp as heatshields cover it, but if you can get a hold of prop and it thumps up and down in centre, mount has collapsed.
worth a try.

 

[television]

hi, in my experience, when pinion bearings are
worn they are noisy all the time not just under deacceleration,
can I suggest prop centre mount has collapsed as prop drops down
under deacceleration and lifts its self back up under the load of acceleration,
its quite awkward to check even on a ramp as heatshields cover it, but if you can get a hold of prop and it thumps up and down in centre, mount has collapsed.
worth a try.

Sorry I disagree here pinion bearings have behaved like this since 1920.

A prop shaft cannot whine, it can knock and vibrate and cause shaking, but never whine

 

[tjoneill@btconnect.com]

hi malcolm,

 

[television]

hi malcolm,

Hello, and how are you

 

[tjoneill@btconnect.com]

hi malcolm,
JFDI was complaining of a whirring noise not a whine,
I'll be interested to know what cures this car

 

[tjoneill@btconnect.com]

sorry, yes I'm good, dont get time to look at forum very often now
but just thought I would stick my oar in

 

[television]

hi malcolm,
JFDI was complaining of a whirring noise not a whine,
I'll be interested to know what cures this car

Fair comment, and point taken, and it would be very good if you are correct.

What the OP can do is to jack one rear wheel, and by rocking the wheel backwards and forwards, while someone watches the prop shaft, if it moves up and down too much in the center, then it could be the prop center of flexy end couplings.
I must agree, that the OP said that it happened after spinning a wheel, and this should not damage the diff, unless the strain damaged a roller bearing.

Any one who knows cars could drive it and know what it was instantly .

I would much rather it be you that is correct, rather than me

 

[tjoneill@btconnect.com]

time will tell malcolm, altho we will have to agree to disagree about a pinion bearing
being able to be noisy only acceleration or deacceleration, if the car is moving then the
pinion is spinning so bearing would be noisy all the time like a wheel bearing whereas if it was the crown wheel and pinion that were noisy then certainly it can be noisy under acceleration
or deacceleration depending on weather wear on front or back of teeth.hope that makes
sense

 

[television]

time will tell malcolm, altho we will have to agree to disagree about a pinion bearing
being able to be noisy only acceleration or deacceleration, if the car is moving then the
pinion is spinning so bearing would be noisy all the time like a wheel bearing whereas if it was the crown wheel and pinion that were noisy then certainly it can be noisy under acceleration
or deacceleration depending on weather wear on front or back of teeth.hope that makes
sense

Sorry you miss the point here and pinion bearings, it is not the bearing that whines, its the teeth on the crown wheel that makes the sound. When the bearing are good the pinion is in perfect mesh with the teeth on the crown wheel, when the bearings go, the gears are mating at the edge of the teeth, and it is this that make the noise. In the over run this the pinion is tipped, and the opposite side of the teeth are used.

I have re built many, though in those days the pinion housing was removable making an easy repair

 

[meanie]

The puzzle here is that it's not related to speed.
Is it possible that you caught the exhaust,a heatshield or an undertray & that what you can hear is a resonance which is apparent as a result of the torque reaction of the power train?