Limited Slip Differential

[roastbeef]

driftflo how do you feel about using the oem recommended oil without FM for our oem diffs? is there a better oil to use without FM to improve the feel and performance of the oem diff?

[driftflo]

Originally Posted by roastbeef

i'm interested in hearing more of your input. what would you recommend for a street driven m3 that spends about 8 days a year at the track? i would be looking to improve the feel of my car, but its a little while before i can make this jump.

- medium locking rate on power and coast
- low to medium preload
- steep ramps >40°
- grinded and grooved (or drilled) molybdenum clutch material

with this setup you will have a great handling car that is not too snappy and has no understeering issue.
and it lasts very long before you need to rebuild (>50.000 miles street driving... and even after 100.000 miles there would be some lockup left).

most important is, that the above setup is built correctly and with the right clearances, materials, hardness of surfaces, ...
not every so called diff builder will deliver a unit that you are happy with although you have given him the above clues.

[driftflo]

Originally Posted by roastbeef

driftflo how do you feel about using the oem recommended oil without FM for our oem diffs? is there a better oil to use without FM to improve the feel and performance of the oem diff?

you should not use an oil without fm additive in the OE diff!
you also should not use the bmw "fm booster" oil.

i suggest "castrol syntrax limited slip 75w-140". it has the right amount of fm additive in it so that the lsd can still lock.
but you cannot fight against the delay in lockup of the oe lsd with any oil.
without any fm the clutches will wear quickly and with the fm booster oil it can hardly lock properly any more.

[roastbeef]

do you build/service/sell diffs or something? its obvious to me you know what you're talking about.

[GeorgeA]

Originally Posted by driftflo

if he was racing a gt4 there would be no need to change the lsd... but it needs to be rebuilt quite often. after one season of racing the performance has dropped massively. but once opened you can make it more durable easily.




amg has a very soft throttle response on the m156-powered cars... it may feel that the diff locks lately but this is due to the torque that comes with a little lag (but then it comes massively making it a little harder to control the car with the lsd spinning both wheels). furthermore, only since the new generation with turbo engones cars are equipped with an lsd in stock config. so if you have driven a c63 w204 (even with performance package) it may have had no lsd at all. and then the car drives horribly indeed!

nissan has even worse viscos in most of their s-chassis, z-fairlady and skyline cars :-(
the bmw m-variable is indeed better then that. an upgrade is strongly recommended for these cars as well.

ferrari 360 should have worked quite well but you really have to push a mid-engined ferrari quite hard to judge on the lsd. you can hardly test this on the street. and it depends on the condition of the lsd of course.
as i wrote above these units do wear... so if the car had some miles on it and was driven spirited it may simply be worn out.
ferrari always did a good job on the lsds used, even in the older cars. and i also like the new e-diffs pretty much. i do a lot of track driving with the new 488 and the car performs great on the edge... no matter if you go fast or sideways. and although i prefer driving it unfiltered with everything turned off, the side slip control (ssc2) that also interacts with the lsd is great for non professional but ambitioned drivers. it really helps you exploring the limits and even go beyond but safes you if anything goes out of control.

I guess my comparisons were mainly to street cars with stock LSDs.

Very helpful, good to know, thanks! Will definitely be checking out your thread on the different diff options for the m3 when its time to refresh.

[driftflo]

yes, i am doing this as a business!
as i wrote, i built +700 lsds in the last 6 years...

and i am working as an instructor for drifting and racing. so i have a lot of possibilities to try and test the stuff i build. and this gives me the possibility to drive a lot of sportscars on the limit... this is great fun but also helps me comparing good stuff to even better stuff...

[GeorgeA]

Originally Posted by driftflo

you should not use an oil without fm additive in the OE diff!
you also should not use the bmw "fm booster" oil.

i suggest "castrol syntrax limited slip 75w-140". it has the right amount of fm additive in it so that the lsd can still lock.
but you cannot fight against the delay in lockup of the oe lsd with any oil.
without any fm the clutches will wear quickly and with the fm booster oil it can hardly lock properly any more.

I can attest to this, that's what I use in my diff and seems to be working well! I believe that is the OEM fill for W204 C63s with the LSD option.

[GeorgeA]

Originally Posted by driftflo

yes, i am doing this as a business!
as i wrote, i built +700 lsds in the last 6 years...

and i am working as an instructor for drifting and racing. so i have a lot of possibilities to try and test the stuff i build. and this gives me the possibility to drive a lot of sportscars on the limit... this is great fun but also helps me comparing good stuff to even better stuff...

Only if you were closer! We would all have a shop to go to. I don't think California has anyone who builds diffs properly, non that I have heard of at least.

[driftflo]

Originally Posted by GeorgeA

I believe that is the OEM fill for W204 C63s with the LSD option.

correct!

Originally Posted by GeorgeA

Only if you were closer! We would all have a shop to go to. I don't think California has anyone who builds diffs properly, non that I have heard of at least.

yes, there are really few people out there who have deep knowledge on how to set a lsd.
i ship parts and lsd cores worldwide but sending one single core or some clutches to the US is quite expensive. it would make more sense to work with a US company which distributes these parts, rebuild kits and lsd cores. maybe this will be an option for the future...

[driftflo]

here for example is an osg install:
http://www.limitedslip.de/service/einbau_osgiken.html

and here drexler gt4:
http://www.limitedslip.de/service/einbau_drexler.html

c63 gearset and lsd change:
http://www.limitedslip.de/service/einbau_c63.html

german language... but the pics speak for themselfes i hope!

[roastbeef]

Originally Posted by driftflo

you should not use an oil without fm additive in the OE diff!
you also should not use the bmw "fm booster" oil.

i suggest "castrol syntrax limited slip 75w-140". it has the right amount of fm additive in it so that the lsd can still lock.
but you cannot fight against the delay in lockup of the oe lsd with any oil.
without any fm the clutches will wear quickly and with the fm booster oil it can hardly lock properly any more.

i'm not doubting you, but could you please explain why the 75w-140 castrol syntrax ls is superior to oem? better thermal capacity? better feel?

[Candide13]

Originally Posted by driftflo

here for example is an osg install:
http://www.limitedslip.de/service/einbau_osgiken.html

and here drexler gt4:
http://www.limitedslip.de/service/einbau_drexler.html

c63 gearset and lsd change:
http://www.limitedslip.de/service/einbau_c63.html

german language... but the pics speak for themselfes i hope!

Thanks for chiming in with more excellent pro input! It would be great if more of this kind of specialized bespoke diff service was available stateside. For the price of a shiny set of wheels one could contemplate a potentially significant and customizable high-tech performance upgrade...

Maybe you could sell through Turnermotorsport or a similar high reputation race-oriented US vendor?

Anyhow, fun times in the old country (I am from Germany originally, but that's a long time ago).

[Mvez]

Originally Posted by driftflo

- medium locking rate on power and coast
- low to medium preload
- steep ramps >40°
- grinded and grooved (or drilled) molybdenum clutch material

with this setup you will have a great handling car that is not too snappy and has no understeering issue.
and it lasts very long before you need to rebuild (>50.000 miles street driving... and even after 100.000 miles there would be some lockup left).

most important is, that the above setup is built correctly and with the right clearances, materials, hardness of surfaces, ...
not every so called diff builder will deliver a unit that you are happy with although you have given him the above clues.

THIS

[driftflo]

Originally Posted by roastbeef

i'm not doubting you, but could you please explain why the 75w-140 castrol syntrax ls is superior to oem? better thermal capacity? better feel?

ok, lets start simple...

a "normal" diff-oil has no fm-additive at all.
castrol syntrax ls 75w-140 has a certain amount of fm additive.
bmw castrol fm booster has much more fm additive in it.

"fm" stands for "friction modifier" what already explains quite well what it does...

just think of some "soft soap". the clutches inside a lsd need a certain amount of this soap to slide properly on each other. if there is no soap at all, the friction between the surfaces is too high and the clutches wear out quickly and make bad grinding noises.
on the other hand, if there is too much soap between the surfaces the friction is too low and the clutches just slide easily without much resistance.

so you need a certain amount of "soap" (aka "fm additive") that the clutches slide but still have a decent amount of friction and resistance to being able to lockup.

so why does bmw then use too much "soap" in their booster oil?
many people complained about noisy and grinding diffs while driving a tight corner. this can be due to normal lockup or (more likely) due to some wear issues of the diff internals as the m-variable wears quite quick. as bmw does not have/sell replacement lsd cores or spare parts (and if they would, no one could install them) the only solution would be a new rear axle pumpkin... that would cost a lot of money (either bmw or the customer).

as most people do not even know what a lsd is, how it works and what benefits they do have from it, the easiest solution for bmw to settle complaining customers is to just put in some extra soap and the noise is gone... as is most of the locking capability of the lsd... but rarely any customer will complain about the latter.
and in the meanwhile they put this fm oil in every lsd-diff instead of waiting until a customer is explicitely complaining.

makes sense for bmw... but not for a spirited m3 driver.

[bigjae1976]

Just search diff noises...that will give you your answer on why BMW loaded the the OE oil with FM.

I know Mobil 1 75w-140 doesn't have a lot of FM in it because I get groaning noises at low speeds.

As far as a performance upgrade...I would go with a clutch type diff before I swapped in shorter gears. If you've got good throttle control...driving is a lot more fun. You get to feel the connection between the throttle and the rear axle. It sounds stupid but it's like a good seat...it just enhances the feel, communication and fun!

As far as speed and times...I think there's an easy 1-2 seconds per lap that's on the table in the HPDE environment...that's my guess.

[roastbeef]

Originally Posted by driftflo

ok, lets start simple...

a "normal" diff-oil has no fm-additive at all.
castrol syntrax ls 75w-140 has a certain amount of fm additive.
bmw castrol fm booster has much more fm additive in it.

"fm" stands for "friction modifier" what already explains quite well what it does...

just think of some "soft soap". the clutches inside a lsd need a certain amount of this soap to slide properly on each other. if there is no soap at all, the friction between the surfaces is too high and the clutches wear out quickly and make bad grinding noises.
on the other hand, if there is too much soap between the surfaces the friction is too low and the clutches just slide easily without much resistance.

so you need a certain amount of "soap" (aka "fm additive") that the clutches slide but still have a decent amount of friction and resistance to being able to lockup.

so why does bmw then use too much "soap" in their booster oil?
many people complained about noisy and grinding diffs while driving a tight corner. this can be due to normal lockup or (more likely) due to some wear issues of the diff internals as the m-variable wears quite quick. as bmw does not have/sell replacement lsd cores or spare parts (and if they would, no one could install them) the only solution would be a new rear axle pumpkin... that would cost a lot of money (either bmw or the customer).

as most people do not even know what a lsd is, how it works and what benefits they do have from it, the easiest solution for bmw to settle complaining customers is to just put in some extra soap and the noise is gone... as is most of the locking capability of the lsd... but rarely any customer will complain about the latter.
and in the meanwhile they put this fm oil in every lsd-diff instead of waiting until a customer is explicitely complaining.

makes sense for bmw... but not for a spirited m3 driver.

thank you. i have a basic understanding of how an lsd works as well as FM. obviously what you're recommending has less fm, but how much less? will it be noticeable on the track if i'm really in-tune with my car?
also, if i'm not mistaken, this oil you're recommending has a heavier weight than oem. does that help out with anything? gear lash?
i'm a big fan of subtle drivetrain mods. i have solid bushings and a carbon drive shaft. i'm hoping to improve feel and performance, but i also want to improve my knowledge and understanding of how exactly it is being achieved.

[roastbeef]

i had a hard time finding it in the US, but ecs tuning actually carries 75-140 in a differential service kit- if anyone is wondering. free shipping right now, too.

[bigjae1976]

Originally Posted by roastbeef

i had a hard time finding it in the US, but ecs tuning actually carries 75-140 in a differential service kit- if anyone is wondering. free shipping right now, too.

You could get redline 75w-140NS and then add FM yourself. I'm sure you could call redline and get some dosing recommendations.

Id bet the redline 75w-140 will have less FM than OE.

[roastbeef]

I already picked some up but thanks.

[rymerc]

Originally Posted by bigjae1976

You could get redline 75w-140NS and then add FM yourself. I'm sure you could call redline and get some dosing recommendations.

Id bet the redline 75w-140 will have less FM than OE.

I just changed my rear diff fluid to Redline 75w140 (with no added FM) and it seems alright. Definitely locks up (eventually) and doesn't chatter at all. Now this thread has me worried about accelerated clutch wear

[Mvez]

I've been using Millers Oils in my engines and gearboxes for a few years now, with outstanding results. It's not cheap, but it works. Use to use Mobil 1 Delvac (997 Cup car gear oil) in my 997 gearbox, would get too hot and cause shifting issues....switched to Millers and immediately problems went away, and could use in the hottest summer conditions with no issues. Since then, never looked back.

Has Nano-tech, Indycar/motorsport used, etc. etc., it's the real deal.

For the M3, I would use either Millers Oils NT 75W140 LS, or Motul Gear Competition 75W140. Both handle heat extremely well, and have just a little bit of LS additive to let the LSD work. I'm sure the Castrol is perfectly fine too, it always seem to work in my E46 M3 (non FM booster version). I'm sure I'll try the non-LS though....without a LSD oil cooler, temps get hot, and LS additive just makes things more slippery. For example, Miller's Oils will advise track users to use the NON-LS version for LSD/transaxles for this same reason.

I've been using Millers NT 75W110 (non LS) in my 987 transaxle (tranny and LSD all in one case) with an OS Giken with good results. The LSD locks REALLY well. For a transaxle, it's a compromise as the gearbox works best with 75W90 but the LSD really needs 75W140 (impossible to run Giken 80W250 oil in Porsche transaxle), so have been playing with weights and LS/non-LS to see what I like the best. Going back to 75W140 LS next to see if it smooths out the locking action a bit more. Late in sessions, the gear oil gets super hot, and seems to cause the LSD to lock harder....987's didn't come with factory tranny cooler. So the thicker oil should hold up better, and just have to make sure to warm up the gearbox before hammering down.

For 997 GT3, you could get away with 75W90 because it had a true motorsport cooler for the tranny.

For the M3, no compromise is needed, just run what works best for the intended LSD. Giken, definitely use their oil....for all other LSD's, I would probably run 75W140 for track work.

Gear oil is definitely another tool in your box for tuning....

[Mvez]

Just did a back to back drive with my M3 and my 987. I had to take 987 out of winter hibernation for a back road blast....and man, the difference between the stock M3 LSD and the OS Giken in 987 is huge. So easy to feel the coast (off throttle) stability of the Giken, and the lock on throttle and under braking. These cars are both on similar tires, shocks, and spring rates.

In comparison, the M3 feels downright unstable. Corner entry stability could be hugely improved....you can really feel you have a totally open diff....this is where even low pre-load and low locking factor ramps would really help with inducing a little understeer. It's the high speed stuff where the car needs more stability. I'm not adding aero, so the LSD will definitely help.

I was going to try and live with mine for a while, but after this latest drive, I'm calling Diffs and getting the upgrade started.