Best diff fluid without friction modifier?

[8600RPM]

All oem diff fluid has the friction modifiers in it and I'm looking to get the most performance and not a,quiet diff so looking to change it. Can't find castrol syntax 75-140 anywhere which is what oem uses. Do they still make this or any other recs?

[Datka]

Here we go
https://www.carpartsdiscount.com/dif...ml?3593=545783
I got it in a Mercedes dealership when I changed mine.

[roastbeef]

is there any reading or experiences to share that this actually increases performance? i'm interested.

[Datka]

Originally Posted by roastbeef

is there any reading or experiences to share that this actually increases performance? i'm interested.

This is from another thread:
3. Change the diff oil to the standard Castrol diff oil without FM booster.

I changed mine recently, draining out the BMW oil with extra FM booster and replacing it with Castrol SAF-XJ 75w-140.
The benefits are that the tendency for the less loaded rear wheel to spin up is reduced or eliminated.
A big reduction in the TC light coming on.
Less instability in rear grip under hard acceleration.
In MDM the diff locks up much quicker rather than one wheel spinning up causing the TC to kick in and reduce power.

Diff oil history:
E46 M3:
Factory OEM fill was Castrol SAF-XJ 75w-140
BMW produced their own packaging containing Castrol SAF-XJ 75w-140 with extra FM additives only for customers who complained of noise.
E9x M3:
Same as E46 except (my dealer tells me) sometime around 2010 the BMW Castrol oil with extra FM became the OEM fill.
About the same time Castrol SAF-XJ was rebadged as Castrol Syntrax Limited Slip 75w-140.
Note that the Castrol diff oil above already contains friction modifying additives.
The additives have to allow easy slip between the clutch plates without judder over a large oil temperature range yet lock up completely when clamped together at full operating pressure.
At some tepid temperatures however the additives struggle to allow the clutch plates to slide smoothly over each other and the resulting "slip/stick" effect is heard as a light groan when cornering. This is considered to be a normal function of a high performance LSD. Adding more FM additives to the diff oil (as in the BMW repacked oil) will quieten the diff at the expense of raising the clamping pressure at which the clutch plates are fully locked against each other....IOW the clutch plates slide easier over each other which allows more single wheel spin up and delays the locking action of the Diff when rear tyre grip is lost.
If you do switch to standard Castrol diff oil and find that the diff becomes too noisy (mine is still quiet) then you can either add some concentrated FM (from Opie for instance) or just drain and refill with the BMW oil.

[Killerfish2012]

Run royal purple 75W 140. It's the best there is.

[roastbeef]

thanks for taking the time to find that. will any 75w140 without friction modifiers work? like if i wanted to do research on other specific brands?

[Rassilon]

I always feel the m diff to be laggy when accelerating hard, maybe the FM are the reason? I used dctf-1

[surlynkid]

If this is for the track, why are people running DSC or MDM on? First improve your driving to turn it off. That'll get you better performance. Is this some kind of workaround to leave it on?

[italyix]

Originally Posted by Killerfish2012

Run royal purple 75W 140. It's the best there is.

Until the purple pigment decides to coat all your components.

I use redline 75-140 without the modifier in my diff and have no complaints thus far. Also use redline in engine and transmission, 0-40 and D4ATF

[dparm]

Originally Posted by 8600RPM

All oem diff fluid has the friction modifiers in it and I'm looking to get the most performance and not a,quiet diff so looking to change it. Can't find castrol syntax 75-140 anywhere which is what oem uses. Do they still make this or any other recs?

Before you go putting a non-FM fluid in, check out my thread on BITOG about this very thing:
https://www.bobistheoilguy.com/forum.../against_FM_in



The OEM fluid is Castrol SAF-XJ (now called Syntrax LS) but it has extra friction modifier. If you want the version with "normal" FM dose, the Mercedes fluid is that. ECS also sells the Castrol-branded version.

[pbonsalb]

I was thinking of dumping the factory fill (version with FM) that I put in 2 years ago for Redline Heavy Shockproof. I can light up my 285/35/18 PSS way too easily and I am just modded N/A. But maybe the fluid won't make any difference?

[dparm]

Originally Posted by pbonsalb

I was thinking of dumping the factory fill (version with FM) that I put in 2 years ago for Redline Heavy Shockproof. I can light up my 285/35/18 PSS way too easily and I am just modded N/A. But maybe the fluid won't make any difference?

I wouldn't use Heavy Shockproof. Those are weird fluids and I've yet to hear Red Line ever conclusively recommend it for a street car.

I would stick with an LS-specific 75w140. If you want less FM, just get the normal version of Castrol Syntrax LS 75w140.

[dparm]

Originally Posted by edwardgtxy

I always feel the m diff to be laggy when accelerating hard, maybe the FM are the reason? I used dctf-1

Speed sensitive LSDs are not known for their fast-locking.

Also, DCTF-1 is the dual-clutch transmission fluid. It's basically a 75w85 with some extra additives. You should NOT be using that in the rear diff!

[warp10]

been using the motul stuff and its great

[dparm]

Originally Posted by warp10

been using the motul stuff and its great

There are three Motul 75w140 gear oils. Which one are you using?

Gear Competition LS
Hypo Synt LS
Nismo Competition Oil 2189E

[warp10]

Originally Posted by dparm

There are three Motul 75w140 gear oils. Which one are you using?

Gear Competition LS
Hypo Synt LS
Nismo Competition Oil 2189E

Comp the first one

[bigjae1976]

Redline makes a 75w-140NS which has no FM in it.

[roastbeef]

So who has used one of these oils without FM that tracks and noticed a difference?

This isn't the same feeling that people think they feel between different brands of the same oil weight?

[Z K]

You can just buy the Castrol OEM fluid without FM. It's much cheaper too.

https://www.ecstuning.com/News/BMW_E...l_Fluid_20651/

[Z K]

Originally Posted by roastbeef

So who has used one of these oils without FM that tracks and noticed a difference?

This isn't the same feeling that people think they feel between different brands of the same oil weight?

I'm running the fluid without FM. I don't really notice a difference on track. I get a clunk now and then when the diff is cold and I'm turning while parking.

[SYT_Shadow]

Originally Posted by Z K

You can just buy the Castrol OEM fluid without FM. It's much cheaper too.

https://www.ecstuning.com/News/BMW_E...l_Fluid_20651/

This is what I use

[kolosy]

resurrecting an old thread, sorry. i was going to change my diff oil (and replace an output shaft seal while i'm in there), and realized that i have 2 bottles of LM GL5 75-140 sitting in my closet (left over from my M Roadster). Any issues with using that, or should I buy something else from ^?