LSD, discuss

[greg_atlanta]

Found this on fresh alloy, originally from 350Z manual:

"The VDC system uses a Brake Limited Slip Differential (LSD) system to improve vehicle traction. The brake LSD system works when one of the driving wheels is spinning on a slippery surface. The brake LSD system brakes the spinning wheel to distribute the driving power to the other driving wheel.

If the vehicle is operated with the vehicle dynamics control system turned off, all VDC and TCS functions will be turned off. The brake LSD system and ABS will still operate with the VDC system off. If the brake LSD system or the ABS is activated, the slip indicator light will blink and you may hear a clunk noise and/or feel a pulsation in the brake pedal. This is normal.

While the VDC system is operating, you may feel a pulsation in the brake pedal and hear a noise or vibration from under the hood. This is normal and indicates that the VDC system is working properly.

The computer has a built in diagnostic feature that tests the system each time you start the engine and move the vehicle forward or in reverse at a slow speed. When the self-test occurs, you may hear a clunk noise and/or feel a pulsation in the brake pedal. This is normal and is not an indication of a malfunction."

Got me thinking... I know the Q45 uses a "real" LSD (limited slip differential). If the 350Z and G35 coupe (and maybe G35 sedan later?) are using a brake LSD, is this a bad thing? A good thing? Just an example of cost cutting?

I can't say that I fully understand what a "real" LSD does, but to simplify the matter, I see it as a proactive redistribution of power (whereas a TCS type system is reactive).

I guess no LSD isn't such a bad thing as long as your careful accelerating in turns. Wheelspin can be fun, right?

[PalmerWMD]

A real LSD accomplishes limited slip mechanically, using depending on the system variable slip discs and/or variable viscosity (due to temp changes during slippage).

"Electronic" systems use the brakes and/or retard the throttle to accomplish somehting similiar.

The mechanical LSD actaully helps performance and ET's whereas the electronic systems lower performance in most situations.And are more suitable to enhance tracion during low traction situations (ice etc)

The best situation is to have both and have the TCS or related technology switchable to off.

Fred...

[PalmerWMD]

In the last few years additional technologies have surfaced that use diffenrential braking on all 4 wheels not just to prevent slippage or locking (the other extreme) but to assist handling/control in extreme driving situations.

Depending on how aggresive the software is (or is switched to), they can help control cars that are in a spin or about to enter one, or are loosing their adhesion to the pavement in a curve (or about to do so).

Critics of VDC systems have said they reduce teh drving expereince , while others say they give greaterr confidence to teh driver to push it.

In some settings some VDC's are known to start differential braking or throttle retardation in relatively mild (*by our standards) manuevaers.

While many VDC have a sport mode where the VDC acts as a safety net rather than a nanny.

THe Infiniti VDC's (vehicle dynamic control) are of the less interventionist type, which is meant to leave the drivign experience purer and make sporty driving still fully possible.

Fred....

PS: Sorry 'bout all the typos, but i dont feel lieke editing too much tonite..:pface

[Q45tech]

The viscous LSD module inside the diff costs Nissan close to $500.Why a new diff runs $2500 vs $1500 for an open type like used on all Lexus.Besides the normal function of dividing the torque between both rear wheels.Works in conjunction with the automatic rear toe in during deceleration to keep both rear tires in sync after the first full rpm of spin.

When the Q alignment is set absolutely correctly and the bushings are not worn there is a serious amount of rear toe in added when you decelerate either by down shift or lift throttle or braking ......the more the deceleration the more the toe in amount . Pretty good automatic stability control without adding parts.

Ever heard of lift throttle oversteer? Not on a Q. Why you power out of the apex of a right hand curve the torque shifts the corning weight from the left to the right.

What they don't tell you is the rear brakes are not strong enough to control the full force of the engine so there is always some engine control to limit launch. Also the transmission is weak in the sense that it cannot take full power for long so they limit things in 1st gear to improve durability.

The other problem is I am not sure the OLD [R200 as used on J&Q] viscous unit will take the stresses of the torque multiplied gearing on G35 5/6 speed....the 260 x 13 x 0.85=2873 lb/ft vs 2300 lb/ft on the 90 Q and less on the 94 and newer......the 300zxtt used a larger stronger even more expensive R230 diff.

Now I know the JWT NOX adds goobs of torque but I have seen cases where the viscous has failed [99% wouldn't realize it] on stock Q from on the car high speed balancing and other cases where one rear wheel was held stationary while the viscous spinned the other wheel.

Thats one of the reasons I replaced my diff the viscous was only operating at 25% at best!

[EWT]

Ever heard of lift throttle oversteer? Not on a Q.

You say that like it's a good thing. There's a reason Stillen sells the kits to defeat RWS on Zs and people with first generation Talons and Eclipses modify the rear trailing arms to defeat a passive RWS setup that does similar things to the one on the Q. I personally want to be able to control the rear end with throttle input rather than having the rear suspension think for me and hate the non-linear response you get from RWS. It starts out feeling ok at corner entry, then starts to push more and more as the rear wheels toe-in. I had my old Q on a skidpad once and it was determined to understeer at the limit no matter what I did with the throttle. Safer for bad drivers, but not nearly as much fun to drive as a non-RWS car. It would be interesting to try it with the new one with the active rear sway bar to see if it behaves any differently.

Using traction control instead of a LSD is a cost cutting measure and a poor substitute for a proper LSD. While they're at it, Nissan should really use a torsen rather than a viscous unit

[AGM]

I know most you guys will think putting a 9" in the Q is sacreligious, but my diff conversion has worked really well.

I had Harrop make up a custom billet aluminium housing that fits straight into the Q with a custom cradle and ABS sensor position. No holes to the floor or chopping of any metal to accomodate the larger diff. Everyone who sees it thinks it is factory, which is exactly what I wanted.

The housing allows me to run a real 4:11 gear ratio with 31 spline strength.

The best thing is the gear LSD (Truetrac) which gives me the strength of a LSD without having to maintain clutches due to the way I drive the car.

Because the LSD is a gear set up, it has a progressive lock up over a maximum half wheel rotation, so the lock up is very smooth but direct.

I know this conversion is not for everyone but it has acheived my desired aim of smooth, strong and serviceability.

Regards

AGM

[reggiegsd]

The reason to defeat the Hicas on a 300ZX is to improve the initial turnin feel. There was always an argument over its usefullness on the street, some said it limited trailing throttle oversteer, others said no. I always found it too complicated for the limited benifits. Removing it is a standard modification for cars used on the track. The weight savings is a good thing also.

[DenverQ]

HMMM now you guys got me wanting to remove my HICAS.

I thought it was supposed to help with all that stuff, but i guess not.

How hard is it to remove?

[Sopdadope]

I wouldn't remove it on a Q. Sure on a 300ZX and even the 240SX it gave the cars a vague turn-in feeling IMO but it works very well on a Q and the Skyline, and most everything large, trucks included. I've driven a Q with HICAS and making U-turns is much easier and quick lane changes on the highway seem tighter.

[Q45tech]

The combination of the HICAS 15.9 mm rear bar and smaller [28 vs 29 mm front bar] lowers the front roll stiffness by 13/2=6.5% and raises the rear by 11% to reduce the anytime under steer by 6-7-9% so the toe changing steering works positively with these bar changes.

The active Q needs the 20 mm rear bar to achieve similar results without HICAS.

Most of the 300zxtt that drop the HICAS already have an even larger rear bar 24-26 mm [vs 19-22mm stock] so they have fixed the problem without understanding that the larger rear bar they installed first caused the problem.

If you delete the HICAS or just disable it with a fuse pull always trade up to the 20mm rear bar! As you already have the smaller 28 mm front bar.

[DenverQ]

What if I go with a 20mm bar? would that throw everything out of wack? or would I gain nothing?

I remmebr reading that if you go with a stiffer bar in the rear is make the front barless stiff or somehting like that

[Q45tech]

Unfortunately the whole problem is one of tire nonlinearity! The Q extra weight on the same load carrying capacity tires means that all slip angles are greater than the 300zx at the same speed in the same corner.

The only way to improve [get the slip angles down] is to improve the load rating on the Q tires and this impossible in the 215/65/15-225/50/15 size....even 245/45-50/16 are low rated [unless you buy the close out Yok AVS I tires with a 1630 rating roughly 110 pounds or 7% better load rating. Same with many 255/50/16 they can handle more weighthttp://www.auto-ware.com/setup/slp_hndl.htmThe slip angles would improve by about this amount and the G force capability would improve by half of the gain or 3.5% plus whatever stickson was gained by the 160 treadwear soft compound.

When you add a rear sway bar you are stressing the rear tires more and this extra weight shift control trades rear traction by making them work harder.....they can never work as hard as the front because of the front weight bias but they get closer.

[DenverQ]

Interesting!!! very good reading

I think im gonna go buy the sway bar out of the 91A that is wrecked near me. They only want 85 bucks for it so all I would need is the bushings for the bar!!

[Jberger]

I HATE traction control when it's used as a substitute for proper mechanicals.

Nissan simply cheaped out on the LSD, and it will show up on the track or any time you try and drive in snow/ice.

Had the same discussion with the salesrep who demoed the G35, he kept insisting the traction control was the same as a true LSD, saidly mistaken.

[Stoneage_Turbo]

so a properly load rated low profile tire would decrease slip angle too right? since the smaller sidewall area has less to flex?

now if one wanted to correct "some" front drive push , they would run like a 195-60-14 in front and a 195-65-14 in back ?

or would they run a wider ???/ 60/14 tire in front than the backs 195/60/14?

im not sure if you have went over slip angles and how they realte to tire sizes yet have you Q45tech? i remeber lots of tire sizing and load ratings , so you must have ,just lost my memory i guess

i ask waaaaay to many questions ....

[greg_atlanta]

I think im gonna go buy the sway bar out of the 91A that is wrecked near me. They only want 85 bucks for it so all I would need is the bushings for the bar!!

Speaking of leftover sway bars... does anyone have (or know where to find) a used bar from a Q45t? (16 mm)

Might be fun to try for $75-100. Can't justify paying $200+ for a new Q45a bar.

[DenverQ]

If i get that 20mm bar and like it ill sell you mine greg

[greg_atlanta]

Thanks... guess shipping it would be weird.

Anyone know how many bushings are required?

[911/Q45]

2 frame bracket bushings and 8 end link bushings.