Could dry lubricant coating impair differential ?

[edave]

Hi, this is my first post on the BITOG forum. Such a pleasure to find auto enthusiasts !

I wish to rebuild a differential for a BMW E46 M3, and coat lightly gears and bearings with a dry lubricant (W2S or Boron nitride). The coat is sub-micron. But this could raise some issues that maybe you are aware :

-Since dry lubricants are extremely slippy, could it contaminate clutch disks and change the behavior of the locking function ? The differential is M-variable.

-When rebuilding, preload is the key. But, if the internals are very slippery the preload reading could be impaired. And when the dry lubricant will fade bearings will have a hard time ? Or is the preload not related....


The purpose of this is to maximize the life of the diff which is very expensive normally to change by your dealer. It is a total ripoff and the non serviceable philosophy rebuts me. There are alternatives for this matter (better internals Quaife/OS) but since it is my first ever rebuild I wish to keep the stock internals. I will also change oil more regularly so maybe contamination could be a non issue plus there is the "GM friction modifier", as last resort.

Thanks

 

[zeng]

If the dry lubricants is not polar in nature, it shouldn't interfere with operation of limited slip differential.

Preload in differential is mostly about very tight clearance to slight interference fit on pinion shaft assembly for desired rigidity.This rigidity would be compromised only by excessive clearance caused by highly worn bearing rollers holding the pinion shaft gear.

JMHO.

 

[RooflessVW]

If you're worried about durability under severe use, I would have the components shot peened and cryotreated in lieu of a solid-film type lubricant.

 

[Doog]

Originally Posted By: edave

The purpose of this is to maximize the life of the diff which is very expensive normally to change by your dealer.
Thanks


If you want to maximize life then forget the dry lubricant and do three things:

1. break in the differential (200 miles) with mineral based 80w90 gear lube. Then drain.
2. Use a synthetic gear lube that is higher rated than the OE standard (if the standard is 75w90 then use a 75w110 or 140.
3. Use a gear lube with the FM already in it and change it at 75% of the OEM interval.

 

[MolaKule]

Quote:
If you're worried about durability under severe use, I would have the components shot peened and cryotreated in lieu of a solid-film type lubricant.

Quote:
If you want to maximize life then forget the dry lubricant and do three things:

1. break in the differential (200 miles) with mineral based 80w90 gear lube. Then drain.
2. Use a synthetic gear lube that is higher rated than the OE standard (if the standard is 75w90 then use a 75w110 or 140.
3. Use a gear lube with the FM already in it and change it at 75% of the OEM interval.

Quote:
-Since dry lubricants are extremely slippy, could it contaminate clutch disks and change the behavior of the locking function ? The differential is M-variable.

Yes they will slough off and cause chatter problems later on.

 

[stchman]

Originally Posted By: Doog
Originally Posted By: edave

The purpose of this is to maximize the life of the diff which is very expensive normally to change by your dealer.
Thanks


If you want to maximize life then forget the dry lubricant and do three things:

1. break in the differential (200 miles) with mineral based 80w90 gear lube. Then drain.
2. Use a synthetic gear lube that is higher rated than the OE standard (if the standard is 75w90 then use a 75w110 or 140.
3. Use a gear lube with the FM already in it and change it at 75% of the OEM interval.



How is the wrong viscosity gear oil "higher rated"?

 

[edave]

Thank you for you responses, all are very appreciated.

Well for shot peening here in Switzerland there isn't many services like in the US, sadly. You're all very lucky ! For cryo treating since it's small pieces it can be done easily if the DIYer can get hold of some LN2... I've read that the metal can become brittle and you should know the exact composition for cryo treating but it should be okay for this kind of steel.

Ring and pinion gears that are already REM polished from BMW Motorsport is available but it is very expensive (1300$) for a 4.10 ratio without shipping to Europe.

As for dry lubricant "slough", is it that bad ? F1 teams use them and I'm not talking about soft teflon... something infinitely small like Tungsten Disulfide that is hard and doesn't peel.

-Since we're here... for example the image illustrate a smooth finish with REM finish. Do you lot know how to micro polish yourself with good results ? There is a lot of methods : tumbling, chemical, plasma. The untreated one look so rough.

For the fun of it I wish to do it with conventional ways, if possible. Does very fine grit polishing (>P10'000) will reduce surface harshness or is it useless ? Any clues ? Or what effective way to reduce surface harshness without interfere dimensions... Not looking for perfect job it is impossible just an improvement.

 

[Doog]

Originally Posted By: stchman
Originally Posted By: Doog
Originally Posted By: edave

The purpose of this is to maximize the life of the diff which is very expensive normally to change by your dealer.
Thanks


If you want to maximize life then forget the dry lubricant and do three things:

1. break in the differential (200 miles) with mineral based 80w90 gear lube. Then drain.
2. Use a synthetic gear lube that is higher rated than the OE standard (if the standard is 75w90 then use a 75w110 or 140.
3. Use a gear lube with the FM already in it and change it at 75% of the OEM interval.



How is the wrong viscosity gear oil "higher rated"?


It will withstand more heat and shearing before it fails. Not really higher rated simply more durable and will withstand more punishment.

 

[Doog]

I forgot one more thing....

Do NOT break the diff in on the highway. Stop and go driving is best. Getting the diff set up correctly is more important than any finish.

 

[zeng]

Originally Posted By: Doog
Originally Posted By: stchman
Originally Posted By: Doog
Originally Posted By: edave

The purpose of this is to maximize the life of the diff which is very expensive normally to change by your dealer.
Thanks

If you want to maximize life then forget the dry lubricant and do three things:
1. break in the differential (200 miles) with mineral based 80w90 gear lube. Then drain.
2. Use a synthetic gear lube that is higher rated than the OE standard (if the standard is 75w90 then use a 75w110 or 140.
3. Use a gear lube with the FM already in it and change it at 75% of the OEM interval.

How is the wrong viscosity gear oil "higher rated"?

It will withstand more heat and shearing before it fails. Not really higher rated simply more durable and will withstand more punishment.


+1

.... for replacing 75W90 with 'heavier' 75W110 or 75W140 for increased longevity of expensive differentials.

 

[RoadRaceJosh]

What's wrong with your differential?

 

[zeng]

Originally Posted By: edave

-Since we're here... for example the image illustrate a smooth finish with REM finish. Do you lot know how to micro polish yourself with good results ? There is a lot of methods : tumbling, chemical, plasma. The untreated one look so rough.
For the fun of it I wish to do it with conventional ways, if possible. Does very fine grit polishing (>P10'000) will reduce surface harshness or is it useless ? Any clues ? Or what effective way to reduce surface harshness without interfere dimensions... Not looking for perfect job it is impossible just an improvement.


Edave,
Any marginal reduction in surface harshness with any surface treatment,doesn't matter how primitive is the method, would help in longevity of differentials.
On top of that, a 'heavier' grade GL5 like xxW110 and xxW140 is most cost effective in further enhancing longevity of ANY differentials ...... even REM finished product from BMW would derive great benefit from 'heavier' gear oils.

Gear surface wear,if any, would increase gear backlash. It would NOT interfere with preload/rigidity of pinion shaft assembly if pinion bearing wear protection is good.

 

[edave]

Thank you all for responses !

Originally Posted By: Doog
I forgot one more thing....

Do NOT break the diff in on the highway. Stop and go driving is best. Getting the diff set up correctly is more important than any finish.

I wasn't aware before some days ago... Some diff builders, as OEMs, say that there is no need for break-in for differentials. But others stipulate that it is important. Also I won't be using new clutch disks as it is not necessary for 60k Miles, and since the diff is not meant to be serviced normally (thank you BMW) it is already a feat to find bearings and pieces (special thanks to online contributors about this). But as a precaution, a break-in will be done.

Originally Posted By: Joshua_Skinner
What's wrong with your differential?

It is making sort of rubbing/humming noise on full turns in 1st gear and dealer says it has too much backlash. Apparently for E46 M3 life expectation is at best 80k Miles.

For the info, this can be fixed with fluid that contain friction modifier (GM's). Maybe it could be solved with it but if the dealer is correct, then backlash is the problem.

Originally Posted By: zeng
Any marginal reduction in surface harshness with any surface treatment,doesn't matter how primitive is the method, would help in longevity of differentials.
On top of that, a 'heavier' grade GL5 like xxW110 and xxW140 is most cost effective in further enhancing longevity of ANY differentials ...... even REM finished product from BMW would derive great benefit from 'heavier' gear oils.

Gear surface wear,if any, would increase gear backlash. It would NOT interfere with preload/rigidity of pinion shaft assembly if pinion bearing wear protection is good.

Okay good that you cleared this out !

After research BMW use from factory 75w140 weight.

 

[zeng]

Originally Posted By: edave
Thank you all for responses !
It is making sort of rubbing/humming noise on full turns in 1st gear and dealer says it has too much backlash.
Apparently for E46 M3 life expectation is at best 80k Miles.


Strange ...........
Does BMW begins with high initial backlash in factory ???
...then if need be, adjust backlash before 80K miles or now while you are at it.

Originally Posted By: edave
Originally Posted By: zeng
Any marginal reduction in surface harshness with any surface treatment,doesn't matter how primitive is the method, would help in longevity of differentials.
On top of that, a 'heavier' grade GL5 like xxW110 and xxW140 is most cost effective in further enhancing longevity of ANY differentials ...... even REM finished product from BMW would derive great benefit from 'heavier' gear oils.
Gear surface wear,if any, would increase gear backlash. It would NOT interfere with preload/rigidity of pinion shaft assembly if pinion bearing wear protection is good.

Okay good that you cleared this out !
After research BMW use from factory 75w140 weight.



Doog's rule of thumb of 'heavier' viscosity grade oils for differential longevity still applies .............

...more so with potentially high initial backlash setting from BMW factory !

80W140 is a worthwhile proposition for it's durabillity (it won't be too thick) ............

even if REM finished products are in use.

 

[SOHCman]

I wonder is a QPQ (quench, polish, Quench) Melonite process could be beneficial to the parts?

Certainly works in firearms, but still a different animal.

I seem to recall Ford re-speced lots of truck differentials to 75w-140 from the -90 for the durability improvement.

 

[zeng]

Originally Posted By: SOHCman
I wonder is a QPQ (quench, polish, Quench) Melonite process could be beneficial to the parts?
Certainly works in firearms, but still a different animal.



Differential gears are heat-treated by carburizing for surface hardness. Gear sets undergoing another form of carburizing in QPQ process, besides gaining hardness, also benefit in gear tooth surface smoothness for longevity.



Originally Posted By: SOHCman
I seem to recall Ford re-speced lots of truck differentials to 75w-140 from the -90 for the durability improvement.



+1 ..... kudos to Ford!
This benefits consumers, at the expense of parts sales ............

 

[DoubleWasp]

Originally Posted By: SOHCman
I wonder is a QPQ (quench, polish, Quench) Melonite process could be beneficial to the parts?

Certainly works in firearms, but still a different animal.

I seem to recall Ford re-speced lots of truck differentials to 75w-140 from the -90 for the durability improvement.


Chrysler fid the opposite and back-spec'd the 9.25" corporate axles to a 90. Stupidest recommendation I never followed.

 

[LeakySeals]

I have an 06 Escalade AWD that needs the front and rear diff fluid changed. If I go with 75w140 synthetic versus the factory 75w90 synthetic will I see my gas mileage go down?

 

[zeng]

At super light load,short trip and subzero ambient temperature ..... possibly,if detectable.

At medium load, > 5 mile trip, possibly not.

But one thing is certain, components protection is vastly enhanced.

JMHO.

 

[Kiwi_ME]

Originally Posted By: edave
Originally Posted By: Joshua_Skinner
What's wrong with your differential?

It is making sort of rubbing/humming noise on full turns in 1st gear and dealer says it has too much backlash. Apparently for E46 M3 life expectation is at best 80k Miles.

Sounds to me like the issues are with the limited-slip components rather than the ring and pinion. I would be cautious about interpreting what the dealer means by "backlash," again unlikely to be in the main gearset.