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GT-R has a limited slip diff in the front?


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#1 drs_gtr

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Posted 23 July 2012 - 12:28 PM

I assume the GTR does have a limited slip differential in the front, since it uses the same fluid as the 1.5 way rear diff, but I have been unable to find anything that specificly says the front is an LSD.

Anyone know for sure what type of diff is in the front? If it is an LSD, is it a 1 way or 1.5 way?

#2 Martin Donnon

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Posted 23 July 2012 - 01:02 PM

No - open wheel front differential :)

Edited by Martin Donnon, 23 July 2012 - 01:02 PM.


#3 RPM

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Posted 23 July 2012 - 01:33 PM

Has anybody found any benefits on track with running a front LSD on the GTR? I read somewhere that this causes the AWD system to get "confused" and go into 2WD mode.

#4 MindlessOath

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Posted 23 July 2012 - 01:58 PM

There are aftermarket front LSD's. i have seen specs with them installed but not heard anything about the performance and handling characteristics of them.
all we know is that with a mostly unmodified TCM the os giken front diff has some issues. Cobb tuning was testing the Front LSD for OS Giken.

im think someone said it was a ecu/tcm issue. it may need testing with say a syvecs to get 100% or maybe its a hardware issue with the part? maybe a tuner with a syvecs can trouble shoot it? martin?
http://www.nagtroc.o...otorports-gt-r/

The only problem from the weekend was a bizarre front diff issue. Bo be clear, it wasn’t a front diff issue at all. Our new OS Giken front LSD was functioning perfectly, it was the brain of the GT-R that was confused. Imagine that. For some reason the lack of differential front wheel spin was causing the ECU to not demand FWD from the center differential. The result was a kind of a RWD car for the weekend, although worse because the FWD would go on and off, creating an exciting ride behind the wheel with 700+ lb feet of torque, and a chassis not setup for RWD only. But with a lot of sideways driving and a set of corded RA-1’s later, we got the results we wanted which included the new track record for a Modified Class car.


Here are some other Aftermarket front LSD's.
http://www.speedfors...lsd-p-1251.html (1 Way)

http://www.speedfors...lsd-p-1715.html (Carbon 1.5 way)

http://gt-rr.com/pro..._version&id=277

http://justjap.com/s...productid=20372 (NEW? or misslabled?)


for front diff cooling which Nismo also run a similar solution on the R35 in race mode...
http://www.gtrblog.c...rential-cooler/
i dunno if anyone else makes a front diff cooler also.

#5 RPM

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Posted 23 July 2012 - 03:33 PM

Yup, that's the only article I have read which provides feedback on the effects of a front LSD for the GTR. I am hoping race teams who run a front LSD can chime in as well or if we can get additional feedback from Cobb if they solved the issue with the AWD system turning into RWD mode only.

#6 MindlessOath

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Posted 23 July 2012 - 03:50 PM

possibly a torque split controller issue rather than ecu/tcm. thats what someone suggested to me (he can chime in if he would like to be named).
the syvecs doesnt talk to this and i dont think the cobb does either.

its possible but unknown if the unreleased motec does. i know that HKS has an ATSC which can distribute torque but i dunno if that works with aftermarket front LSD or solves the issue.

#7 the King

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Posted 23 July 2012 - 05:43 PM

Why would anyone want to run LSD with how the current ATTESTA system is setup? Would love to know the answer from the knowledge persons...
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#8 TodZilla

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Posted 23 July 2012 - 05:51 PM

My questions is....... Would the center diff be able to deliver enough torque for a front LSD to make any difference? and ......... Will the front diff housing be able to tolerate the addition loads applied with the application of a front LSD?

I am def not the resident expert but putting it out there.
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#9 MindlessOath

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Posted 23 July 2012 - 06:01 PM

from what i gather when it worked for cobb it worked well, they just couldnt get it to work full time.

Zavodney, with all the cracked front LSD housing's, i dunno, you may be right, but we also dont know why that happens 100%. someone suggested it happened when the fluid leaked out when the bolt came loose. others have had it happen when doing donuts. one person was at either drag or road corse and about 7-800whp and it cracked. but whats actually causing it and the fix for that?

I really dont know much. was hoping some of the vendors could get a front lsd and do some testing and fiddle with the torque split controller or whatever. im guessing if a customer doesnt bring it to there attention no one will do anything about it (so i guess thats my way of saying someone needs to get vendors motivated by funding the research?).

#10 Martin Donnon

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Posted 24 July 2012 - 02:03 PM

The stock ATTESSA pro system R35 AWD is pretty good - at least the way it distributes torque front/rear
Once you change the way the front makes traction (add LSD) you are going to create masses of understeer when the torque biases forward (ATTESSA still thinks you have an open front diff driving one wheel, not two). Same thing occurred with older R32 - R34 GTRs however their ATTESSA seemed far less active at turn in and midcorner than the R35 system hence you could get away with it. I know back in the day when R32 GTRs dominated Australian saloon racing there were a whole selection of different front LSD setups with different ramp angles used to suit the track being raced on. Its a complicated field :)

#11 elf_cruiser

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Posted 24 July 2012 - 02:25 PM

I'm one of the peeps that's blown up a front diff. I'll post some pics of the damage when I get the busted parts back. After seeing it out of the car, I'm not surprised at all. The front diff and housing was not built to handle any real power. It's about what you would find in a honda civic. I'll take some accurate measurements as well. But in any event, I wouldn't plan on putting too much stress on it. The way it was explained to me by a leading GTR tech is: "The front half of the drivetrain was only really designed to assist the rear enough so that the rear tires don't spin during a hard launch." - So, in other words, our cars weren't designed to be a 50/50 equal AWD system. It's more like RWD with front "assist".
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#12 RPM

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Posted 25 July 2012 - 12:42 PM

I really dont know much. was hoping some of the vendors could get a front lsd and do some testing and fiddle with the torque split controller or whatever. im guessing if a customer doesnt bring it to there attention no one will do anything about it (so i guess thats my way of saying someone needs to get vendors motivated by funding the research?).


+1 It would be interesting to see if a front LSD in combination with a tuned center diff would yield improvements on track. Or if it's simply not worth the effort with the ATTESA and the TCM systems creating the best traction in most scenarios on track.

#13 Martin Donnon

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Posted 25 July 2012 - 01:49 PM

The way it was explained to me by a leading GTR tech is: "The front half of the drivetrain was only really designed to assist the rear enough so that the rear tires don't spin during a hard launch."


That is not correct in any way.

#14 elf_cruiser

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Posted 25 July 2012 - 02:41 PM

Interesting Martin. Can you elaborate? Or perhaps explain why the front diff and axles are so much weaker than the rear components?
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#15 Martin Donnon

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Posted 26 July 2012 - 04:04 AM

I suppose the simplest answer is that the front diff and axles are double de-clutched by the rest of the driveline. There is the GR6 conventional twin-clutches plus the FWD clutches that isolate them from shock-load which is what normally breaks driveline parts. The application of the FWD differential is controlled via software in the transfer case, which allows its size to be fairly well minimised whilst still being reliable under most driving conditions.

Edited by Martin Donnon, 26 July 2012 - 04:05 AM.


#16 RPM

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Posted 26 July 2012 - 07:56 AM

It is my understanding that in an open diff setup power will always travel through the easiest path. i.e. tire with the least amount of traction. With an LSD, when traction is limited with a tire you get progressive lock up with the diff effectively matching wheel speeds from the tire that's slipping to the tire that still has traction, limiting wheel spin and powering both wheels.

With the GTR's ATTESA system, there is active F/R shifting of power and L/R power management is controlled by the LSD setup and the TCM by having the ability to brake individual wheels. My question is does the GTR's TCM system create somewhat of a "synthetic" LSD in front by braking individual wheels limiting wheel spin and therefore transfering power L/R?

I could be completely off base here. I am anticipating some sort of correction with the above description.

#17 elf_cruiser

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Posted 26 July 2012 - 10:52 AM

I suppose the simplest answer is that the front diff and axles are double de-clutched by the rest of the driveline. There is the GR6 conventional twin-clutches plus the FWD clutches that isolate them from shock-load which is what normally breaks driveline parts. The application of the FWD differential is controlled via software in the transfer case, which allows its size to be fairly well minimised whilst still being reliable under most driving conditions.


That's a very good technical description of the parts involved - but I think everyone on the thread ?probably? already understands the parts involved. I know I do.

When I look at this drivetrain as an entire system - it really does appear to me to be a RWD system, with front assist. And everything you just described lends credibility to that observation. A true 4 wheel drive vehicle (trucks, jeeps, etc) would never dream of using a center differential. The F&R drivelines are directly connected with no clutch in between so that whichever end of the vehicle has grip can use 100% of the engine's torque. And as such, the Front and Rear differentials and axles are generally similar in overall strength, usually a bit more in the rear than the front, but close.

Looking at the GTR, however, not only does it have a center diff that "protects" the front end by limiting the amount of torque sent there, but the GTR also has that FWD clutch before the fron output shaft, which further limits the amount of toqrque that can be delivered to the front end. All this adds up to my assumption/observation/whatever you want to call it/ that they are not expecting the front tires to ever do more than 50% of the work in moving the car. And therefore, they felt they could "get away" with using smaller and lighter components in the front half of the drivetrain, due to the "protection" that the center diff and FWD clutches provide.

That's just how i see it, looking at things from an overall strength perspective... The car is great, but the front end is not built to be as strong as other AWD cars that I've owned (Audi)

EDIT: RPM - yes that's correct. Lots of manufacturers are now using the brakes to act like a LSD. The first one I recall off-hand was land rover in the late 90's. The one's I've driven work OK, but not that great. In the off-road world, you really need lockers or spools. In the road racing world, a LSD in the rear is a must have, but in the front, I'm not so sure - I think it would mess with the steering quite a bit (think torquesteer in FWD cars) during corner exit, and possibly produce throttle understeer. On the drag strip, however, I think it would help if you are making enough power to spin the fronts during launch - I dunno, I'm not much of a drag racer...

Edited by elf_cruiser, 26 July 2012 - 10:58 AM.

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#18 Martin Donnon

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Posted 26 July 2012 - 01:59 PM

I suppose none of this comes as much of a surprise to us in Australia as we have had all models of GTR here since 1991. Its always been a primarily RWD device with FWD assist which has made it very different from the conventional Rex/Evo FWD with RWD assist. Early GTRs frightened many a motoring journo in Aus due to their ability to drive sideways under power :)

In this respect the R35 is the tamest of all GTRs.

#19 Craig

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Posted 26 July 2012 - 06:02 PM


<snip>

When I look at this drivetrain as an entire system - it really does appear to me to be a RWD system, with front assist. And everything you just described lends credibility to that observation. A true 4 wheel drive vehicle (trucks, jeeps, etc) would never dream of using a center differential. The F&amp;R drivelines are directly connected with no clutch in between so that whichever end of the vehicle has grip can use 100% of the engine's torque. And as such, the Front and Rear differentials and axles are generally similar in overall strength, usually a bit more in the rear than the front, but close.

<snip>


The distinction I've always heard is 4 wheel drive is the transfer case/no center diff arrangement you mention. All wheel drive (AWD) uses the center diff and can control the torque split front and rear (which you can't do with pure 4 wheel drive). 4 wheel drive may be the weapon of choice for offroaders on loose surfaces, but the static coupling is hardly ideal for road/track cars on pavement to produce decent handling...

#20 elf_cruiser

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Posted 27 July 2012 - 11:37 AM

A pic of my broken front diff -

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