The W201 differential refresh thread

[mb201]

Thanks alot for the guidance! Is there someone selling this friction tool? I dont really understand the part :Note: Do not unlock double hex. collar nut with
crush lock, but just loosen.

The collar nut must unlocked to remove the flange?

Stretch i read and learn from forum threads, are you a mecanich?impressing work you have done and info you provide in this forum!

[Stretch]

Originally Posted by mb201

Thanks alot for the guidance! Is there someone selling this friction tool? I dont really understand the part :Note: Do not unlock double hex. collar nut with
crush lock, but just loosen.

The collar nut must unlocked to remove the flange?

Stretch i read and learn from forum threads, are you a mecanich?impressing work you have done and info you provide in this forum!

If you look back through the thread you can find a method of making your own tool. Otherwise you need a torque wrench that has a dial indicator (rather than click). These are expensive...

...the nut does indeed need to be unlocked - "de-peened".

I'm not a professional mechanic (any more - used to work on aircraft) I consider myself to be an enthusiastic amateur.

[mb201]

Ok, what range of dial wrench iam looking for, is it the same as a digital torque wrench? Is it accurate the metod you made? Iam just thinking about when you do a little at the time torque on the nut to get the correct torque, its maybe easy to do a little to much and thats it..And maybe not so easy doing this when diff is still boltet on car.

How about cut some new slots for the old nut in the pinion so it will be possible to lock?

[Stretch]

Originally Posted by mb201

Ok, what range of dial wrench iam looking for, is it the same as a digital torque wrench? Is it accurate the metod you made? Iam just thinking about when you do a little at the time torque on the nut to get the correct torque, its maybe easy to do a little to much and thats it..And maybe not so easy doing this when diff is still boltet on car.

How about cut some new slots for the old nut in the pinion so it will be possible to lock?

If you do an image search for "dial torque wrench" in your favourite search engine you'll see the type I mean. A digital torque wrench might not work as well. I don't know - never tried.

The idea is to measure the rolling friction of the system and set that back to where it was after removing the nut replacing it and the seal.

The method I made is to measure the stiction. This is different from the rolling friction but so long as it is repeatable for several different starting positions you should be good. It will probably be as near as damn it.

It is indeed harder to get repeatable results if the differential is fitted to the car and still fitted to the axles and the wheels. You are then measuring a whole lot more friction / stiction. Still this is the method of fixing that seal as per the FSM. Have you read / found the chapter yet?

As for the nut.

Well you should replace. It isn't that expensive. If you are lucky the other side of the nut could be used to peen. But if the new peening place is too close to the old staking / peening then the material is likely to be fatigued and it is unlikely it will do the job of locking the nut in position.

The pinion in a differential has a hard life. Every time you accelerate or deccelerate the pinion wants to pull or push its way out of the casing. This backwards and forwards motion is going to quickly make nuts (that aren't fixed properly) come undone.

[mb201]

Yes i found the dial, but thinking it must be very low on the torque? how about using a strap around the pinion for about 5times and have weight on the end, check how much weight i need to turn pinion? Thinking it maybe better option with diff. in car. Is there no one selling the friction instrument that MB use?

Yeah it was in my mind about the hardness of the pinion, have been reading the procedure from MB. Its not the cost of the nut that is problem, but thinking its the easy way of fixing this and most "accurate" with old nut back to same position. And if i have one more peen + loctite +180nm it must last for a while, iam not racing with this car. Maybe check the nut from time to time.

Thanks for reply and sorry for my bad english..

[Stretch]

Originally Posted by mb201

Yes i found the dial, but thinking it must be very low on the torque? how about using a strap around the pinion for about 5times and have weight on the end, check how much weight i need to turn pinion? Thinking it maybe better option with diff. in car. Is there no one selling the friction instrument that MB use?

Yeah it was in my mind about the hardness of the pinion, have been reading the procedure from MB. Its not the cost of the nut that is problem, but thinking its the easy way of fixing this and most "accurate" with old nut back to same position. And if i have one more peen + loctite +180nm it must last for a while, iam not racing with this car. Maybe check the nut from time to time.

Thanks for reply and sorry for my bad english..

Any tool sold by Mercedes comes at a premium! I have spent a lot of time trying to avoid the use of Mercedes tools for this reason - it has almost turned into a new sport for me...

...strap and weight might work - give it a go. But this method needs to be repeatable and reliable. If you mess it up then you kill your differential => the gears will wear unevenly and you'll never get it to be quiet again.

Checking the nut is not really plausible with out removal of the propshaft - not really a regular service interval kind of a thing.

Note also the 180Nm tightening torque might not be what is needed. It could be less because the crush spacer / washer between the two bearings on the pinion shaft has already been compressed =>

On a new installation - with a new crush washer / spacer - the torque needed to compress this spacer is immense (this is why I was starting the crushing process off with a hydraulic press). You are not going to need such a high torque to nudge the nut up against the crush washer a second time (which is essentially what is happening with the seal replacement procedure). If you over tighten the crush washer during this process the friction in the pinion bearings is too great - and the little bearing will probably fail (it is little and has a lower lifetime expectancy)

[mb201]

Ok i see, do you think the friction is below 10nm?

[Stretch]

Originally Posted by mb201

Ok i see, do you think the friction is below 10nm?

The friction of the pinion shaft with nothing else fitted to it should be set to 120-140 N cm (Newton centimeters not Nm!) with new bearings. I assume the combined friction of pinion against crown wheel fitted to axles and wheel bearings would register less than 10 Nm on a torque wrench.

######

I've just checked in the FSM with regards to the 180Nm specification. I didn't realise that that is the minimum needed for this seal replacement procedure (chapter 35-530). If the book says you need to get that minimum torque then you need to comply with the book! It does strike me as a dangerous thing though as over tightening the pinion nut and crushing the washer / spacer too far means you then have to remove the differential from the car - take out the crown wheel etc - take out the pinion shaft and fit a new crush washer...

[mb201]

Think i just check the airvalve and hope it pass the MOT, dont have dripping oil. Just visible after driving, this car dont do much miles in a year and i can refill when necessary. Have a feeling this change will problably do more damage than fix problem. I will do a test checking how much oil coming out, running car in garage on stands. As for the gauge i need can this one help me? Beam Torque Wrench 1 4" Drive Socket Type Style inch Pounds 80 in lb 9 | eBay


I still dont understand this part: Note: Do not unlock double hex. collar nut with
crush lock, but just loosen.

6 Position holding wrench (040) on universal flange
and loosen double hex. collar nut with double hex.
socket wrench element (040a). Use suitable box-end
wrench for supporting holding wrench (arrow).

Note: Do not unlock double hex. collar nut with
crush lock, but just loosen

[Stretch]

It is saying you shouldn't try to destroy the peening on the nut before removal - just try and undo it.

I assume they are worried that if you knock the peening away you might damage the bearings. There's a note for applying the peening later on that says "no strong axial blows"...

...because you are only partially disassembling the differential you are not going to be checking the condition of bearings - this is why I guess they want you to just try and rip the nut away from its locked position.

Ermmm - good luck with that!

[mb201]

Ok, if its that fragile what happens when you start removing the universial flange, the picture show a tool that will pressure the pinion? Phoned a workshop asking about changing this, NO we dont do this job, ok? Yes we had one and it failed, most experience mechanic did job and they had to replace diff. Waiting for MB shop to give a price.. Checked it today with running wheels and cant see any leaks, so its very ilttle over time coming out when driving. Have cleand the airvalve, didnt take the chance of removing, to much dirt and difficult to clean 100%. Must be very special pinion set up on this, WV and Audi was no problem the workshop told me.

Lets say it like this, dont worry about price on tools for this job if option is MB garage doing it...

[spock505]

Hello Stretch, hope all is well in 190 world, can I tap you for some advice please.

My S124 project car is now back on the road having never really had a proper chance to drive under normal conditions. Some background, 126k miles with four speed (722.4) auto OM606.910 oil burner.

Unfortunately it has a whine between 35 - 60mph after which it seems to get a lot quieter. At first I though it may have been the center bearing so changed that for a minor improvement, also changed the front wheel bearings which again afforded some improvement but still very noticeable.

Oil was drained and refilled before putting back on the road however it does leak or seep out some oil, seals?

My only check has been getting under the car to check play on both exit flanges, there's a fair knock perhaps around 2-3mm of play at each end.

So I have decided to replace it or have the unit reconditioned by a diff specialist.

There’s a good supply of used diffs but only one with exact matching numbers but the price is high £400 + with post as is the miles. This is almost the cost of a full rebuild. Other vendors have said the numbers (the ones in your earlier post cast onto the rear cover) don’t really matter, it’s the ratio that important.

Being a ‘glass is half full’ type of person I am naturally keen to believe this, however I do have one or two reservations. So my questions is

a) did you find out what the numbers stand for ..and
b) which if any are not relevant ?

For example, I have been offered a diff with very similar number but mine has ‘30’ as opposed to ‘25’’

Number on diff back plate:

R124 351 30 08 ratio 3.07

Diff for sale

R124 351 25 08 ratio 3.07

One suggestion is to measure the points between the flanges, this I have not tried as yet but might be tricky getting an accurate reading due to the diff part obstructing straight line measurement.

Sorry for windy post but I am going around in circles.

Thanks

[spock505]

I have just re-read your informative thread again and wanted to ask a third (but probably daft) question.

Assuming it's just the axle bearings causing miss-alignment of the crown gears due to wear. Would it not be possible to order new MB bearing using original shims (circ clips) to bring the unit back to factory settings?

Originally Posted by Stretch

It is worth noting that although the position of the pinion and crown wheels is a three dimensional problem the adjustments in practical terms can only be made in two dimensions =>


If the holes for the axial bearings in the differential are not aligned properly then there's little we as mechanics can do to correct for this error. If the centre line of the axial shafts are not at the correct height with respect to the height of the centre line of the pinion then again we as mechanics can't really do anything about it.


You might want to let that sink in! (If you really want to understand what's going on and what could go wrong)




Adjustments are made to the positions of the pinion and the crown wheel by the use of shims.


Shims are placed in three areas in the differential (for the adjustment of the pinion and crown wheel)


The position of the pinion is adjusted by placing a shim behind the inner most tapered roller bearing cup.


The position of the crown wheel is adjusted by adding shims behind the axial tapered roller bearing cups. These shims are circlips!





The circlips are shims!




The position of the pinion is probably going to be relatively easy to measure and adjust. The position of the crown wheel, however, is complicated by the pre-load of the axial bearings.


Bearings need to have a pre-load to stop them from sloshing about within the differential case. Sloshy bearings = noise {because there will be uneven contact between crown wheel and pinion}


At no expense spared here's a scanned in sketch of what is going on.





The position of the pinion with respect to the centre of the crown wheel is distance “x”


The position of the crown wheel with respect to the centre of the crown wheel is distance “y”


Think of the differential case as a great big C clamp. By stretching the C clamp within its elastic limits you can essentially use the springiness of the clamp as a way of pre-loading the axial bearings => you make it bigger than it is – you stick the bearings in there and release the pressure. It is a bit like making an interference fit – you stuff something slightly larger into a slightly smaller hole.


The problem is – and here's where you move from the realms of theory into the realms of practice – the differential case isn't a beautiful uniform homogeneous lump of metal. It is a roughly cast bell shaped thing with holes drilled in it. This means that when you stretch the opening (to get your pre-load for the bearings) one side of the case (y1) might not move as far as the other side of the case (y2).


This is a total bugger when you are trying to set your distance “y”...


...to be continued.

[Stretch]

Originally Posted by spock505

Hello Stretch, hope all is well in 190 world, can I tap you for some advice please.

My S124 project car is now back on the road having never really had a proper chance to drive under normal conditions. Some background, 126k miles with four speed (722.4) auto OM606.910 oil burner.

Unfortunately it has a whine between 35 - 60mph after which it seems to get a lot quieter. At first I though it may have been the center bearing so changed that for a minor improvement, also changed the front wheel bearings which again afforded some improvement but still very noticeable.

Oil was drained and refilled before putting back on the road however it does leak or seep out some oil, seals?

My only check has been getting under the car to check play on both exit flanges, there's a fair knock perhaps around 2-3mm of play at each end.

So I have decided to replace it or have the unit reconditioned by a diff specialist.

There’s a good supply of used diffs but only one with exact matching numbers but the price is high £400 + with post as is the miles. This is almost the cost of a full rebuild. Other vendors have said the numbers (the ones in your earlier post cast onto the rear cover) don’t really matter, it’s the ratio that important.

Being a ‘glass is half full’ type of person I am naturally keen to believe this, however I do have one or two reservations. So my questions is

a) did you find out what the numbers stand for ..and
b) which if any are not relevant ?

For example, I have been offered a diff with very similar number but mine has ‘30’ as opposed to ‘25’’

Number on diff back plate:

R124 351 30 08 ratio 3.07

Diff for sale

R124 351 25 08 ratio 3.07

One suggestion is to measure the points between the flanges, this I have not tried as yet but might be tricky getting an accurate reading due to the diff part obstructing straight line measurement.

Sorry for windy post but I am going around in circles.

Thanks

The part numbers used by Mercedes to identify the differential as a unit are not stamped anywhere on the units themselves. The numbers you can see are indeed just the casting numbers.

To be sure of the numbers quoted from an advert you need to get access to EPC and then see what the official parts catalogue says what is what.

[Stretch]

Originally Posted by spock505

I have just re-read your informative thread again and wanted to ask a third (but probably daft) question.

Assuming it's just the axle bearings causing miss-alignment of the crown gears due to wear. Would it not be possible to order new MB bearing using original shims (circ clips) to bring the unit back to factory settings?

Yes it could be as simple as that.

It might, however, not be as simple as that!


##########


The big long winded process in the FSM is designed to get the pinion and crown wheel gear in (about) the right position. A decent differential rebuilder would then check the wear pattern with engineer's blue. Apparently the trick to getting a representative wear pattern is to check this under load - this is hard to do for the DIY mechanic.

maboyce over on Benz World made a rig to try and do this for his W123 differential =>

1983 300TD - Mercedes-Benz Forum

(That's a massive thread - it will take ages to find the post - when I do I'll update the link)


####


I think the problem with the small case W201 / W124 differentials is that the case is not rigid enough: In service life it relaxes and so this compression across the axial bearings dies. This increases the backlash and so you end up with miserable output to input shaft play and a noisy differential...