Mr needy needs diff help

[spock505]

That's how it feels, asking so many Q's about this car but the list is shortening.

To cut a long story short, the vehicle (S124) had a variety of whines/whistles and general bearing noises when originally purchased.

These have now been reduced to a single high-ish pitched whine in 2nd/3rd gear speed range.

Popped the car up onto ramps Monday with two experienced mechanics (plus me), one of which specializes in classic 124 Mercedes amongst others.

The good news is it appears to be coming from the front diff nose bearing, but unsure as to why. As part of the noise elimination a replacement diff was fitted (getting rid of low down grumble), it is the same size and ratio but obviously off another car.

I played around with the height by turning the washer (marked with red arrow) upside down, this made no difference. Has anyone come across alignment issues/noises with replacement diffs?

There's no vibration at all either visually looking at the prop in gear under power or when driving.

Any thoughts greatly appreciated.

[spock505]

I can understand vibration but not the whine, large roller bearing bathed in oil?

W210 Vibrations Tied to Acceleration/Throttle - Adjust Your Differential Shim! - MBWorld.org Forums

[Frank Reiner]

sp:

Is there a change in the offending whine with change in throttle position? Power on vs. overrun vs. deceleration?

[spock505]

Very slight Frank, when on ramps it's a case of 'catching' the right revs to make the whine happen. When driving it's pretty constant at the speeds above.

I think it's fair to say, more pronounced under some load.

Today, i loosened the center bearing, ran the drive train up 40mph switched off, locked up bolts, same.

Drive train to my eye is pin straight no wobbling or distortion (new center bearing too).

[spock505]

Tomorrow if time permits, I'll drop each half shaft one at a time and run up. If all else fails put the old diff back in to see if that makes a difference.

The high pitched whine just doesn't relate to a big lump of cast iron filled with (new) oil.

[Frank Reiner]

sp:

With loss of preload, or even insufficient preload of the pinion bearings, the axial position of the pinion will shift slightly with torque changes. As the amount of change of the pinion position increases, so too does the noise, and the rate of bearing wear.

As a test of this, collapse the prop shaft enough to move it clear of the pinion flange and tighten the pinion nut.

What is the rear axle support that you are able to run the driveline while on stands?

[spock505]

Yes, good call, perhaps quarter of a turn?

I checked for up/down play but nothing, couldn't detect any movement at all, didn't think lateral play.

"What is the rear axle support that you are able to run the driveline while on stands?"

The vehicle is supported on the two rear jack mounts with wooden blocks.

[spock505]

Differential Pinion Pre-Load Adjustment.

[Frank Reiner]

Originally Posted by spock505

Yes, good call, perhaps quarter of a turn?

I checked for up/down play but nothing, couldn't detect any movement at all, didn't think lateral play.

"What is the rear axle support that you are able to run the driveline while on stands?"

The vehicle is supported on the two rear jack mounts with wooden blocks.

If the rear suspension is in full droop, conflicting noises may be coming from the half-shafts, CV joints, and diff side bearings.

The process of changing the preload, as illustrated in the link, is correct. NOTE how LITTLE movement of the pinion nut is required.

[Stretch]

As Frank has mentioned play in the pinion bearings will cause changes in whine when driving with (abrupt) changes in accelerator position.

If this is happening then it is probably time to get the differential rebuilt.

There are a few things I can think of that might help however but these are rather short term fixes.

As a matter of interest - I assume you've got the larger casing differential fitted (as the rest of your estate parts are on the beefier side)

[spock505]

Morning Stretch, yep, I think Frank is on the money with that call. It has to be something that's not affected by bumps, general car movement, but accelerator position yes.

The original diff is sitting in my garage, will check front bearing float to see if any different (less) than replacement diff unit.

From under the car, there is no up/down play at all, nothing perceptible. I did wonder if the replacement maybe a bit longer, again once out will measure accurately.

If it's just a new pinion bearing hopefully not too expensive?

edit:, larger case, is that for the increased radius gear used on some models?

[spock505]

I appreciate not the most technical approach, but would it be sufficient to tighten pinion nut until light resistance is felt?

On the spare (original) diff there is none, going to check the one currently in use.

From the above link courtesy Bernard Embden's Website

Illustrated below is a detailed drawing of the pinion assembly of a typical differential :
Pinion pre-load is the force (pressure) between the pinion bearings (blue) and the pinion bearing's race (yellow). As the pinion nut is tightened it forces the yoke against a "crush sleeve" (red) that is designed to "control" collapse under force. Not enough force from the pinion nut and the crush sleeve holds the pinion bearings too far away from the pinion race resulting in not enough pinion pre-load. Too much force will collapse the crush sleeve and apply too much pressure to the pinion bearings (blue) against the pinion race (yellow), resulting in too much pinion pre-load.

Too much pinion pre-load cannot be undone. The crush sleeve, once compressed, stays compressed. Backing off the Pinion nut once the sleeve has been compressed does not result in less pinion pre-load, it results in NO Pinion pre-load.

[spock505]

Removed prop shaft today, firstly to make the pinion bearing adjustment but also as a general alignment check.

First problem, my deep impact socket didn't have the depth to overcome output spigot so..opted to swap diff for original, if only to eliminate the whine.

Filled with fresh oil and re-fitted, set off for a test drive..you guessed it..whinnnnneeee....still there.

Whilst disappointing there is some upside, namely all that effort that went into changing the wheel bearings was valid as the diff is okay, smooth as silk.

So I have a spare tested diff which can be sold with some assurance, secondly by the process of elimination there's not much else to replace, lol

The viscous fan was removed a while back as not really necessarily here in UK, so that leaves four, possibly five whirring things:

Alternator

Water pump

Power steering pump

TC rubbing against inside of bell housing




..ladies and gentlemen place your bets please..

[Stretch]

Well if it is an accelerator position related whine then you might have two worn differentials

(The larger cases are not for lower gearing they are just better made)

As for tightening the pinion bearings to try and make that less of a problem it probably won't help much (even if you can get the pinion bearings tighter) partly because

1) the pinion bearings once worn won't actually get tighter within specification - well weird - they just won't - don't know why - even the FSM says once the desired friction can not be obtained you just have to replace the bearings

2) the position of the pinion gear running against the crown wheel is what is making the whine - pinion gear in wrong position == chances of whine + + +

[spock505]

Evening Stretch, change the aux belt shock today along with tensioner arm, again, no change.

When it was on ramps the noise appeared to be coming from around the center bearing, however this was discounted due to new part already fitted.

The noise is not there under hard acceleration but appears once the load is reduced, it comes in straight away once the foot is off accelerator. I think it could be worn or shot engine mounts which are stressing the center bearing, i.e the engine has drooped putting most strain on the drive train.

For me, the noise is exactly the same from one diff to another, i find this difficult as you might at least expect a slight change in tone.

See 'Opinion on S124 engine mounts' thread.

Opinion on S124 engine mounts