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Revision as of 23:54, 9 May 2011

A Limited Slip Differential (LSD) prevents one of the rear wheels slipping. A differential is inside the final drive (ring & pinion) gears and allows the left and right wheels to turn at different speeds. This is important of course for going around corners. The downside is that if one wheel is on slippery ground (ice, gravel, mud, etc) the car doesn't go at all, as one wheel is turning but slipping and the other not turning at all. Hence the usefulness of LSD or locking diffentials, which are typically used on high-performance cars. Locking is typically used on off-road vehicles, LSD for road vehicles, including racecars. Most productions cars did not and still do not come equipped with LSD. Less expensive cars (like the 1200) did not even have it as an option, however Datsun Competition sold an LSD that fit Datsun 1200.

1 Overview
2 LSD
3 Locking Diffs

Overview

Limited Slip Differentials come in many different types, but the main thing is they limit wheelspin. This is useful in racing and in low-traction surfaces (rain, snow, etc). Or for maximum accleration at full throttle. Different types of LSD are cone-clutch, spring-loaded, clutch-pack, hydrodynamic (viscous), etc. Some trademarks are "Posi-Traction" (GM), "Traction-Lok" (Ford), Torsen (Bosch).

A differential is inside the "final drive" (ring & pinion) gears and allows the left and right wheels to turn at different speeds. This is important of course for going around corners. The downside is that if one wheel is on slippery ground (ice, gravel, mud, etc) the car doesn't go at all, as one wheel is turning but slipping and the other not turning at all. Hence the usefulness of LSD or locking diffentials, which are typically used on high-performance cars. Locking is typically used on off-road vehicles, LSD for road vehicles, including racecars.

LSD

Nissan Performance racing parts used to sell a clutch-pack type LSD for the H145, H150 and H165. These parts are NLA, however may be found occasionally in specialty shops or on eBay.

H145

Nissan Performance racing parts used to sell an LSD for the 1200.
H145 LSD (NLA)

Nissan Part Number: 38420-H1020 L/S ASSY H145 (TO 8/74)

Parts

From the 1984 Nissan Competition Catalog:

H145A LIMITED-SLIP ASSY (TO 8/74)

38420-H1020 L/S ASSY
38423-H0120 SIDE GEAR (2)
38424-H0120 THRUST WASHER (1.0MM) (2)
38424-H0120 THRUST WASHER (1.25MM) (2)
38425-H0120 PINION (4)
38427-H0120 PINION MATE SHAFT
38429-H0120 PINION SHAFT
38430-H0120 DISTANCE PIECE
38431-H0120 PRESSURE RING (2)
38437-H0120 CENTER RING
38432-H0120 FRICTION PLATE (1.5MM) (2)
38432-H0121 FRICTION PLATE (1.45MM) (2)
38432-H0121 FRICTION PLATE (1.55MM) (2)
38433-H0120 FRICTION DISC (1.5MM) (2)
38434-H0120 SPRING DISC (1.5MM) (2)
38435-H0120 SPRING PLATE (1.5MM) (2)
08320-61000 SCREW (4)

H150

Nissan Performance racing parts used to sell an LSD for the B210.

Aftermarket H150 LSD

H165

Pitroad sells a brand new LSD for the H165B axle (1985-up Sunny Truck) for about $1200 USD. It is from TRD (Toyota Racing Development) and is a bolt in when using the AE86 ring gear bolts. Pitroad H165 LSD or TRD

You can also buy the AE86 LSD (PN 41301-TA005) direct from TRD, be aware however that this is untested, and probably won't fit most H165 carriers. About $850 USD

TRD Sales NZ

Phantom Grip

Spring-loaded LSD vs. conventional

Torsen Diff

Torsen differential works on a gearing principal and has no friction plates:

Superior limited slip action, unless one wheel loses 100% traction
Superb for street suspension or soft racing suspension, where there is little chance of a wheel coming off the ground
If a wheel comes off the ground it stops working

For more information, see [1]LSD vs Quaife ATB]

Locking Diffs

A "locking" differential is another animal. When locked there is no slip -- not just limited slip, but none at all. When unlocked, it's the same as an open differential. These are used for racing or for seriously slow off-road work.

Locked diffs are also useful for circuit racing. Many race cars from all sorts of categories use locked diffs. The understeer that is apparent on street/drag cars with locked diffs can easily be eliminated with proper (race) suspension geometry. These settings (camber, castor, and toe) will not be practical for street use though.
L18_B110

There are different types of locking diffs.

Air Locker

The ARB air-locker is popular with Jeeps and other off-roaders. When the dash-mounted switch is flipped, air pressure locks the diff gears together

Detroit Lockr

The "Detroit Locker" was used by some high-performance Ford vehicles in the 60s and 70s. The Locker may be the only modern road-going locking differential, as it can automatically lock and unlock. It is sort of a hybrid between an LSD and a Locker.

Spools

For drag racing, the spider gears can be replaced with a sold unit so that both axles are always locked together. This is called a "spool"

spool (right center)

Welded Diff

The "poor man's" locking diff is to have the spider gears welded together so that it works like a spool, but is obviously cheaper. The danger is of a bad weld and having it explode on the race track.

Using a spool or welded diff gears on the street is illegal in most countries, and can be dangerous, especially in the wet. The danger is of spinning out as the wheels do not turn independently, but the inside wheel is forced along the same as the outer.

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LSD