OK...I was wrong. (Atleast I am man enough to admit it...)
Here's a quote to finally put this one to rest:
"In order for a vehicle to go in any direction other than a straight line,
the wheels' speeds must vary from side to side. In 4x4s, this is
accomplished via two shafts per axle; one solid axle would cause both tires
to spin at the same speed. This wheelspeed differentiation happens inside
the pumpkin in, appropriately, the differential. In "open" differentials,
the driveline torque takes the path of least resistance and goes to
whichever side is easiest to turn. This is great for cornering but explains
why one tire in the air turns while the opposite one on the ground remains
motionless. So, the compromise is better on-pavement handling with little to
no tire scrub at the expense of off-road traction. Here's an overview of the
various traction-increasing differentials that are currently available.
LIMITED-SLIPS
Limited-slip diffs (also known generically as "posis" from the
GM-trademarked Posi-Traction) offer the flexibility of allowing wheelspeed
differentiation for cornering but "connect" the axle shafts when either
side-to-side torque difference or wheelspeed exceeds a certain point. Most
LSDs use friction between the differential case and side gears to connect
the axles as opposed to lockers' meshing teeth. Generally, limited-slips are
smoother and quieter on the pavement and inflict less tire wear than lockers
because they transfer less torque per side. This is why some manufacturers
recommend their LSDs for use in front axles.
In technical terms, limited-slips' design intent is to transfer more torque
to the wheel with traction, a process called "torque biasing": the available
ring-gear torque that a given differential can transfer to one wheel when
the other one has reduced traction. Open diffs have 1:1 torque biasing; a
traction diff with a 2:1 torque bias would transfer twice as much of the
ring-gear torque to the wheel with traction as the one without.
Generally, limited-slips are one of four designs: clutch-type, cone-type,
the hybrid limited-slip/locker Eaton Gov-Lok, and planetary-type.
Clutch-type limited-slips are the most common and use spring-loaded clutch
packs between the diff case and side gears to transfer some of the ring-gear
torque to the tire with less traction. When traction loss is sensed, the
diff's clutches transfer the power to the other side by driving that side's
side gears. The spiders gears spread the side gears, which in turn exert
force on the clutch plates. Increased load increases the pressure against
the clutch plates, which transmits power to the wheel with traction.
Preload is provided by springs-the stiffer the spring/higher the load, the
less wheelspeed differentiation the limited-slip allows, making it closer to
the locker end of the traction-diff spectrum than the open-diff end.
Clutch-type limited-slips typically require a friction additive to the diff
oil for optimal operation. However, the clutches and friction area can wear
down over time.
Cone-type limited-slips are manufactured by Auburn Gear. These units use
"cones" that attach to the backside of the side gears that nest in machined
surfaces in the diff case. Under load, the side gear wedges itself to the
case. Because this design requires less force to lock the side gears to the
diff case and there aren't any clutch plates to wear out, cone-type units
typically enjoy long life.
Another limited-slip approach is Eaton's Automatic Locking Differential
("Gov-Lok"), which is a factory rearend option in many GM-built trucks. This
diff uses "governors" to detect differences in axle-shaft speed, and its
gears are activated by cam weights and friction discs when speeds differ by
approximately 100 rpm, thus sending torque to the slower side. When
"locked," the Eaton unit turns both end at the same rate, much like a
locker. However, spring-loaded flyweights keep the units from locking at
over 20 mph for safer cornering. Designed for stock applications, field
reports say that the Gov-Lok can give up the ghost on trucks that have
modified engines and oversized tires. The unit is also more costly than
other limited-slips because of its complicated design and numerous internal
parts.
Finally, the Detroit TrueTrac is a "compound planetary gear" unit that uses
dynamic loading instead of clutches or cones to transmit torque to the
unit's pinion gears. Because the TrueTrac has no springs/preload, light
brake pressure can help transfer the torque.
LOCKERS
Lockers fall into two categories: manual and automatic. Automatic lockers
activate without driver input, transferring all of the available torque to
both wheels as soon as side-to-side wheelspeed differences cause heavy
springs to activate the locker's clutch and engage the spider assembly. The
spider assembly's teeth mesh with those on the clutch members to make both
axle shafts operate as if one solid shaft. This engaging and disengaging can
produce clunking sounds, and one side-effect is possible understeer because
only the inside wheel is driving during cornering. Increased tire wear is
another concern. However, automatic lockers are virtually maintenance-free,
enjoy proven durability, and can usually be installed by any competent
ring-and-pinion mechanic.
Manual lockers-such as the ARB Air Locker and PowerTrax Command
Locker-require the driver to engage the locker by pushing a button. This
allows open-diff steering and handling in high-traction situations but
effectively locks the axleshafts together at the push of a button in
low-traction terrain. For this reason, the respective manufacturers make
both front- and rear-end applications. Also, manual lockers are more
expensive than automatic lockers because of the actuation parts involved,
and installation is more intricate, requiring mechanical, electrical, and
even pneumatic rigging.
Finally, spools are intended for competition vehicles. Used for such things
as mud-bogging, truck pulling, and sand-dragging, spools produce the effect
of one solid axle shaft instead of two, turning both wheels at the same
speed all of the time.
The variety of traction-assisting differentials on the market strives to
provide the most power to the ground in on- and/or off-road situations. "
You can also find it here:
http://www.truckworld.com/How-To-Tech/Lockers-Differentials/4x4Lockers-Diffs
.html
Regards,
Bernd D. Ratsch
Pflugerville, TX
bernd@texas.net
http://lonestar.texas.net/~bernd
"Gonna buy me a Dodge Truck and blow those Fords off the road....."
> -----Original Message-----
> From: owner-dakota-truck@buffnet4.buffnet.net
> [mailto:owner-dakota-truck@buffnet4.buffnet.net]On Behalf Of Bernd D.
> Ratsch
> Sent: Monday, January 18, 1999 6:46 PM
> To: dakota-truck@buffnet.net
> Subject: RE: DML: Re:
>
>
> Now correct me here:
>
> In the "Old Days"...Limited Slip signified that one axle has
> constant power
> (usually the right) while the other (not being under a load) would spin
> freely. This made cornering easier since you only require one wheel to
> provide power, and they would alternate to which ever was under the load
> (Left or Right).
>
> (y old Javelin has a "Limited Slip" axle and when you put it on jacks, put
> it in 2nd for ease of turning, and spin either tire, the other
> one spins the
> other way. If you have a buddy hold on to the left tire, you can
> still turn
> the right...and vice versa. In the other case, my old Camaro
> (12-Bolt Posi)
> turned both wheels in the same direction and you couldn't hold onto one
> while turning the other.
>
> "Posi" signified that both wheels turned at the same time and
> were "locked"
> together. (Remember the old days when you either welded or bolted the
> clutches together on a limited slip...same thing.) This also generated a
> "Chirp" out of the tires when accelerating and turning from a dead stop.
> (Since both tires turned at the same time, the one under less load would
> break free...this also makes POSI slightly less effective on wet/icy roads
> (more fun though).
>
> Comments??
>
>
> > -----Original Message-----
> > From: owner-dakota-truck@buffnet4.buffnet.net
> > [mailto:owner-dakota-truck@buffnet4.buffnet.net]On Behalf Of
> > fawcett@uism.bu.edu
> > Sent: Monday, January 18, 1999 6:05 PM
> > To: dakota-truck@buffnet.net
> > Subject: Re: DML: Re:
> >
> >
> > Well, could be, but I'd just go find a gravel/loose dirt/sandy
> > covered road
> > or a snow covered lot and floor it... If you see two parallel tire
> > (burnout) tracks you have a limited slip. Only one and you have a
> > "standard" diff... Usually the right one is the one that spins with a
> > standard diff., but I don't know exactly why.
> >
> > I would think it's more fun doing it this way too :-) YMMV.
> >
> > T.
> > ______________________________ Reply Separator
> > _________________________________
> > Subject: DML: Re:
> > Author: <dakota-truck@buffnet.net> at smtpout
> > Date: 1/17/99 5:28 PM
> >
> >
> > Powell Wheeler wrote:
> > >
> > > Just bought a 1990 Dakota, 3.9L, 4x4, 51K miles. The motor
> is a little
> > > weaker than I expected but aside from that I'm very happy
> with it. The
> > > owners manual said that some of these trucks had the limited slip rear
> > > differential, does anyone know an easy way to tell my truck has that
> > > feature? The VIN dosen't say.
> >
> > I don't know any #'s or anything, but, if you use a
> floor jack and
> > raise both rear wheels, put it in neutral, when you turn the wheels by
> > hand both will turn at the same time if it's limited slip. If not then
> > the wheel your turning will rotate opposite of the other wheel.
> >
> >
> >
>
>
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