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      01-07-2013, 11:18 AM   #1
driftflo
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Big LSD Shootout... OS Giken, Drexler, Titan, GKN, ZF...

hey guys,

i just started (dis-)assembling and testing some aftermarket clutch-type lsd options for the M3.


competitors i got here so far:

- gkn viscolok (the stock unit)
- os giken superlock spec-s (and custom spec... see below)
- drexler gt4 light
- titan traction master (with a set of sinter and another set of carbon discs)
- zf (which i modified and tuned to my own spec)

i put some pictures of each unit on my website:
http://www.m3racing.de/sperre.html
(text only in german so far... maybe i'll translate it someday)


still missing:

- cusco
- kaaz
- ???


what i've tested so far:


after driving (and drifting) some thousand miles with my stock gkn viscolok unit i was sure to need a proper torque sensing clutch-type lsd which will react and lock/unlock way quicker and with direct connection to gas pedal movements. the viscolok is a really slow performer who locks and unlocks slowly and smoothly.
quite ok for non-performance street driving and slippery, snowy road conditions. but annoying when driving on the track or drifting the car where you need direct control and quick response of your rear axle behaviour.




i first tried the os giken superlock spec-s unit. it fitted perfectly into the rear axle housing, no additional shimming was required. build quality, materials used and the surface finishing is really thumbs up.
but once installed i was pretty much disappointed on the locking capabilities: it hardly locked at all... it simply felt like an open unit.
after discussing with the supplier and manufacturer we were pretty sure that the neg. preload setup was to high. i got some new pressure plates and a different setup suggestion. i am really curious an how it will perform in the new spec which i will assemble these days as i am pretty convinced of the general design and the negative preload idea in theory. i guess i will only need to find a proper setup (which should normally be done by the manufacturer but well...)




right now i am driving the drexler gt4 light unit (out of the M3 GT4 competition model) with the steeper of the two rampsets, more lockup on decel and no preload. it performs a lot better than the above but still doesn't lock as hard as i would want to. so i will flip the center section to get more lockup on accel or i could use the other rampset... i am still thinking on what setup i will try next.
build quality is quite high as well... and it also fitted perfectly without the need to re-shim.



i have two more "competitors" laying around here already:


a titan traction master lsd unit which i got with a set of sinter-coated discs. but as i know the sinter-stuff from my other cars already i am looking forward to get a set of carbon-coated discs soon. i will try this unit with the carbondiscs then! it has some preload and i opted for the symmetrical 2-way ramps.




and last but not least i have an old friend of mine here as well. an "old" zf lsd unit from a M5 E39 which also fits into the E92 rear axle. but as this unit locks quite weak in stock configuration, i am massively modifying this unit to fit more clutchpacks and/or use different ramp angles. this unit is performing well if modified correctly (i did this kind of mods in other m-cars quite often yet) and is still a lot cheaper than all other mentioned units.



i will update this thread whenever i switch the units and have new findings.

when i will finally be happy with the configuration of the current units i have here, i'll get the next bunch of lsds like kaaz and cusco.

if anyone does also drive a aftermarket lsd unit i would be happy to read his findings on it. what manufacturer, what setup, what kind of driving, satisfied with the performance, ...?

would be great to collect all lsd units here which are available for the m3 and discuss about their pros and cons...
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      01-07-2013, 11:37 AM   #2
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This is some really good info. Thanks for putting this together
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      01-07-2013, 11:37 AM   #3
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Cool info.
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      01-07-2013, 11:46 AM   #4
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Nice!
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      01-07-2013, 03:29 PM   #5
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great post! thx 4 takin the time 2 share
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      01-07-2013, 05:12 PM   #6
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Thanks for sharing!

If you did not do drift events, do you think these units would meet your needs for track only?
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      01-07-2013, 05:51 PM   #7
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the drexler and especially the os giken are track-oriented setups in my opinion.
for drifting-only i would have chosen different setups with more lockup and more preload.
i don't judge the units only for their drifting capabilities... i test them at a driving center with various options of u-split (one side slippy, one grippy) tests.
and if course i judge them on how they feel in everyday (hard) driving.
so i think i can finally judge quite well how a certain lsd setup behaves in what situations.
and a dedicated track setup would not necesserily be the same for everybody. a slick-tired, competition coilover, pro-driver driven car would be set up different than a weekend-warrior with street tires and an amateur driver.

if someone wants an lsd having set up from me, i ask a lot of things on the setup and dedication of the car and what behaviour the driver wants. then i would suggest a certain setup, build it and have it tested. in general this fits quite well then ;-)
if someone is not completely happy, i would reconfigure and finetune the setup along the behaviour that was out of what it was expected to be. (but this needs a really skilled and experienced driver really)

the reason for my detailed testing is that i had the impression that no one else really has done it so far (works team in professional motorsport have done and still do for sure but won't share their findings of course).
and when i see what crappy standard setups are being delivered to customers there is definitely a need to test what really works and what doesn't improve performance and traction as much as it could. (it is like fitting a 3-way highend coilover kit with an wired standard setup... you'll need to do a lot of testing to find the best setup for your requirements)

and often, the philosophy of the various lsd builders is completely different. just look at the push/pull locking ratio. cusco sells 1-way diffs for the m3 as standard (no lockup on decel at all), the other japanese companies sell at least 1.5 way setups (some lockup on decel, but less then on accel), zf sets their bmw units to 2way (accel and decel have the same lockup) and drexler even does more lockup on decel than on accel. this is wired indeed. but you can change this easily!
what really makes sense for which driving situation i will try to find out myself.

it became a hobby to me... ;-)
i already tried some dozen different setups in my other bmw race and driftcars.
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      01-07-2013, 07:17 PM   #8
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Wavetrac? Any thoughts?
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      01-08-2013, 04:53 AM   #9
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the wavetrac is a torsen-style atb (automatic torque biasing) unit which biases torque from one side to the other but is not able to lock the axle completely like any clutch-type lsd does.
and a torsen only locks... no, sorry... biases torque on accel and remains completely open on decel. so you have no stable rearend when braking or just lifting the gas.
in case of the wavetrac system you will have some preload compared to conventional torsen designs like quaife, who dont have preload.

so a torsen is a good diff for street driving but doesnt offer the performance of a clutch-type lsd unit. torsens are easier to drive for "normal" drivers as they dont lock/unlock but just smoothly transfer some torque. some supercars with massive torque output (i.e. gumpert apollo) use these units which extends the life of the bodyshell and typical driver of such a car ;-)

as our cars do not tend to be torque monsters and are really easy to handle, there is no need to get a supersmooth diff. and if you want such a smooth unit, it is already installed in stock config. the gkn viscolok is a "good" lsd which is pretty slow. the torsen is also quite "good", quicker than the gkn but with less locking capabilities. so if upgrading a quite well stock unit i would only opt for a really better, higher performing lsd system... and this only is the clutch-type one!

i hope i could explain it in an understandable way...?!

Last edited by driftflo; 01-08-2013 at 04:59 AM.
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      01-08-2013, 08:02 AM   #10
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I think it's pretty cool that the Wavetrac will transfer tq when one wheel has zero friction and still drive the other wheel.
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      01-08-2013, 08:55 AM   #11
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any clutch-type lsd with preload does the same... and you can change the amount of preload by changing the cupsprings.
the downside of preload is understeering! the more preload, the more understeer!
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      01-08-2013, 10:30 AM   #12
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OP would love to hear your thoughts on the stock ///M diff ???
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      01-08-2013, 10:37 AM   #13
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Great info here. Thanks for sharing
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      01-08-2013, 10:39 AM   #14
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Quote:
Originally Posted by Beedub View Post
OP would love to hear your thoughts on the stock ///M diff ???
the stock ///M is the gkn viscolok unit, that i described in my first posting!
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      01-08-2013, 02:41 PM   #15
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Quote:
Originally Posted by driftflo View Post
the stock ///M is the gkn viscolok unit, that i described in my first posting!
thankyou :-) Excuse me, should have read closer :-)
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      01-08-2013, 03:24 PM   #16
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Nice info, thanks for sharing.
Good luck hunting
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      01-08-2013, 04:17 PM   #17
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Thanks for the info
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      01-09-2013, 12:18 AM   #18
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OP what is the stock diff set to on power/coast side ? is it 45/45 ? do you feel like it has too much corner entry and mid understeer ?

What are your thoughts on nitriding clutches to extend the life and maintain the preload by reducing the relaxation of the springs ?

Do you know what is the accel/decel set on drexler gt4 light ?

Aleks.
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      01-09-2013, 03:45 AM   #19
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the stock diff is a speed-sensing unit. it has no accel/decel values as it has no ramps where the diffaxles run up and down generating pressure depending on the torque applied, as in a torque-sensing clutch-type lsd design.
with the stock unit you necesserily need different wheel speeds over a certain amount of time (meaning: one spinning wheel) to activate the sheerpump which generates the pressure on the clutches. the engagement is smooth... as is the disengagement.
so one wheel spins for a short while, diff starts locking smoothly (and can lock up to 100% which means no matter how big the torque difference left/right will get, it remains locked), then after locking a while there is of course no more difference in wheel speeds and the sheer pump will disengage and releasing the pressure on the piston. so the diff opens up smoothly. if there is still a huge difference in traction l/r it will again start from the beginning... on and on...

so with this unit you will have no corner entry and mid understeer at all (except the amount of preload it is set to.... this is what you feel when turning in low speeds and a lot of customers are complaining about... also here in this forum).
but on corner exit, when hitting the gas quite hard, this unit will not lock immediately but let the inner wheel spin for a while. this is when your opponent with a clutch-type lsd will gain several feet... and you have no "direct connection" (via the gas pedal and the currently applied torque) to your lsd as everything happens timeshifted in a speedsensing unit.


shimming the preload spring is pretty silly in my opinion. i know this is done often but for street and track driving it definitely is the wrong direction of modification. for a drifting only car you can drive high preloads.
and keep in mind that this will always lead to higher wear.

concerning nitriding i am no expert. but for the clutches i would not change them out of manufacturer hardness spec. as the inner clutches are molybdenum sprayed i am not sure if you can simply nitride them?! some guys apply some surface finishing (rem polishing) on it. this has no disadvantage and i could imagine it will extend life and reduce oil pollution (a very important point if you drive a porsche with a gearbox-integrated diff).
i only nitride diff-items that were machined and then have no sufficient surface hardness any more.

anyway, i wouldnt waste time and money in optimising a non-optimum stock lsd-unit. if you have no complains about the stock unit leave it like it is. if you want a higher performing, quicker reacting unit, change to one of the above mentioned.


the drexler gt4 has two rampsets on the pressure plates: 40/50 and 50/65 degree ramps (dont mix this with locking rates given in %!!!)
drexler calculates the angles like zf did (based on the vertical zeroline) and this is the opposite way as os giken does (they take the horizontal line... so you need to subtract from 90 to get the "other" values). so in osg language this would be 50/40 and 40/25.

drexler doesnt give lockup rates (as any other aftermarket lsd manufacturer does not either). i calculated the following:
40/50 degree ramps: ~85/70%
50/65 degree ramps: ~70/40%

in standard it is setup for more decel lockup and i think the lower, higher locking values.

i am currently driving 40% accel, 70% decel. this provides to few lockup on accel for me. so i am thinking whether to rotate the pressure rings so i will have 70 an accel and 40 on decel or go with the 70/85 that the other rampset would provide?!

Last edited by driftflo; 01-09-2013 at 04:15 AM.
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      01-09-2013, 04:36 PM   #20
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Thank you for the education OP. Great read!
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      01-09-2013, 09:14 PM   #21
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Very informative thread. Thanks OP!!
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      01-12-2013, 10:56 AM   #22
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Cool thread, love the pics.

Interesting feedback on the OSG Super Lock. I wonder if you got a bad unit? We have sold many of these with nothing but excellent reviews. (circuit, rally and hill climb clients primarily) The most winning BMW team in American circuit racing runs OSG with no issues and we run them in our cars as well. Looking FW to seeing your next attempt with the SL.

Ironically, one of our dealers in Belgium was here in Philly yesterday and he told me he switched from Drexler to OSG in his rally cars (two S54 E87s, one 2.7 S15 E30M3 - all with Drenth sequentials) and it worked MUCH better for his needs.


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