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Locker Comparisons
Understanding Differentials/Lockers
What's A Differential?
When a vehicle
is negotiating a corner, the outside wheel has to travel a grater distance
than the inside wheel. Therefore, the outside wheel must turn faster than
the inside wheel. The differential is the device within the axle assembly
which, in addition to transmitting the power to each axle shaft/wheel,
allows one wheel to turn at a different speed than the other.
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| A conventional open
differential sends equal amounts of torque to both axleshafts (top).
If one wheel spins because of lost traction, it is sustaining zero
engine torque, so zero engine torque is also going to the wheel with
traction. Adding a locking differential—in this case a NoSpin locker
(bottom)—mechanically links the two shafts so that power will be
delivered to both axles in all
circumstances. |
What types of Differentials are there?
Conventional or
Open
Limited Slip
Automatic
Locking
Manual Locking
Open Differentials:
Use two side
gears inside the differential case. Each gear is splined to accept an axle
shaft. These side gears are in turn driven by a set of spider gears. The
spider gears, also inside the differential case, ride on a shaft which is
pinned into the differential case and through which all the power is
transmitted. The case is driven by the ring gear which is bolted fast to
the case. The conventional differential is fitted as standard equipment on
most vehicles.
On paved roads
this system is very successful, giving predictable handling, even tire
wear and requiring very little maintenance. However, in off road
situations where traction surfaces vary greatly, this type of differential
has a major limitation. When one wheel has greater traction than the
other, all the power will be directed to the wheel with the least
traction. For example, if one wheel is in the air and the other wheel is
still on a hard surface, then all the power will be transferred to the
wheel in the air. No power will go to the one on the ground and the
vehicle will not move.
Limited Slips:
(LSD's) come in
a variety of designs. Most use friction plates, cones and/or gears to
reduce slippage between each of the tires. these units have a dual power
path from the differential case to the axle shafts. some power is
transmitted through the spider gears to the side gears in the conventional
manner. The remainder is transmitted by friction between the differential
case and the clutch plates and the side gears. A certain amount of "clutch
preload" is built into the unit in a static condition. Then, as load is
applied to the differential, the separation forces between the spider
gears and the side gears increases this clutch loading. This increase in
friction provides for a good positive power flow from the case directly to
the side gears. When traction is available to both wheels, the power going
to the differential causes the plates to bind tightly together, giving
even power to both wheels. However, in a situation where there is little
or no traction available to either one wheel or the other, the amount of
power that can be transmitted to the other wheel which has traction is
dependent on the friction or "preload" in the clutch plates. High levels
of "clutch preload" will result in good torque transfer but some
chattering of the clutches during cornering may occur. Lower levels of
preload results in minimal chatter but reduced levels of torque transfer
to the wheel with traction. Because LSD's restrict true differential
action, tire wear is accelerated. Changes in vehicle handling may also
occur, particularly in short wheelbase vehicles. Wear rates on limited
slip differentials are generally higher than on other types due to the
reliance on friction to reduce wheel slippage. Also, special lubricants
may be required to minimize rough and noisy operation. Despite their
limitations, LSD's are popular as original equipment options as well as an
aftermarket replace because:
1) Some
traction improvement off road is provided
2) Vehicle
handling idiosyncrasies are not excessive
3) Installation
is simple
4) Cost is
reasonable
Automatic Lockers:
transmit power
to each wheel through a pair of dog clutches. Differential action, such as
when cornering is provided by automatically disengaging the appropriate
clutch when one wheel rotates faster than the other. This results in
differential action which occurs in ratcheting stages rather than being
smooth and progressive. Power received by the differential is
automatically directed to the wheel with greater traction. Therefore, if
one wheel is lifted off the ground, the other wheel will receive the total
power applied to the differential to maintain vehicle mobility. Traction
is far superior to conventional and limited slip differentials. While
automatic locking differential provide excellent performance off road,
vehicle handling, particularly on highway, is sacrificed. Unlocking during
cornering can be sudden, resulting in a rapid change of direction,
particularly in short wheel based vehicles. During sharp cornering an
audible ratcheting sound usually occurs as differential action takes place
and a loud banging noise may be heard when the unit locks up
again.
Tire wear is
usually increase. On 4WD vehicles, installation is normally considered for
the rear axles only. Front axle installations can cause extreme
difficulties in steering.
Manually Controlled Lockers:
use a
conventional differential in conjunction with a mechanical locking device
which can be operated at the driver's discretion. when locked, both axles
will then turn at the same speed irrespective of the road surface. When it
is unlocked, the differential functions as a conventional differential
giving predictable handling, long service life and no increase in tire
wear. It can be installed in both the front and rear axles without
compromising on-road performance. Although manually lockable differentials
are available in tractors and some military style vehicles, the
installation in mass produced recreation type vehicles have been
restricted by high cost and complexity of installation.
The ARB Air
Locker has allowed this situation to be reversed. This unique air operated
unit incorporates its activating mechanism totally inside the differential
center. This avoids the need to have complicated piston arrangements
hanging off the axle housing. Locking action is controlled by the drive
with a push button switch inside the cab. Installation involves a bolt in
replacement of the original equipment differential center, a 12 volt air
compressor with reservoir and an in-vehicle mounted switch. Original
equipment axles, bearings, etc. are retained. Locking/Unlocking of the
unit is extremely rapid approximately 0.1 seconds) and may be achieved at
any vehicle speed. No special maintenance is required and servicing of
other vehicle components is unaffected. Standard lubricants are used. The
ARB Air Locker is the ultimate differential for almost any vehicle
providing 100% drive to each wheel, without handling problems, or
additional wear problems.
Why Do Limited-Slip/Posi Differentials Fall Short?
As the name
implies, limited-slip/posi differentials limit or reduce wheel slippage,
but do not eliminate it. By applying friction with clutches or cones to
the side gears inside the differential, unwanted wheel slippage is
reduced. The degree of reduced wheel slippage is determined by the amount
of friction, or "breakaway torque," applied to the side gears. While
performance varies from one design to another, as little as 15% to 25% of
engine torque will be delivered to the higher traction wheel when new and
will decline with use. Although better than open differentials,
limited-slip/posi differentials do not provide the maximum traction
capabilities of locking differentials.
What Is A Locking Differential?
Unlike
limited-slip/posi differentials, locking differentials deliver 100% of
engine torque to both wheels, even if one has zero traction. Locking
differentials, commonly referred to as "lockers," are available in either
manual or automatic configurations: Manual lockers operate like open
differentials when deactivated. When manually activated, they deliver
maximum traction by essentially joining together both wheels. Because
manual lockers do not differentiate when activated, care must be used to
insure they are manually disengaged when making turns on hard surfaces to
avoid potential damage.
Automatic
lockers deliver maximum traction without requiring manual activation and
deactivation. The wheels are mechanically "locked" together when the
vehicle is traveling straight ahead. As the vehicle begins to turn, it
automatically; unlocks to allow required wheel differentiation throughout
the turn, and then automatically re-locks. Although not as smooth and as
quiet as limited-slip/posi differentials, vehicles equipped with automatic
locking differentials provide differentiation and the highest level of
traction output.
Two Types Of Lockers:
There are
essentially two types of lockers that can be installed in an axle.
One that replaces the whole carrier and one that installs in the
carrier.
The Detroit
Locker and ARB Air Locker are tow examples of lockers that replace the
carrier. They require that the ring and pinion be removed and set
back up. These lockers are not easy for the basic driveway mechanic
and should be done by a reputable mechanic/shop.
The Lock-Rite
is a very popular locker and installs by replacing the side and spider
gears. It installs in to the stock open carrier and can be set up by
anyone with good mechanical skills.
Of the two
designs, the Lock-Rite is much cheaper than the Detroit Locker because
your not replacing the whole carrier. It is also much easier to
install. The Lock-Rite is idea for moderate trail use while the
Detroit Locker should be used in extreme wheeling conditions.
There Is One More Device Not Yet Discussed:
Spools, like
lockers, can be bought as either a replacement for the stock carrier or as
a unit to install in to the stock carrier. Spools permanently lock
the axleshafts together and should only be used in straight line drag
racing or in loose dirt/mud. Spools should not be used on the street
because they will not let the axleshafts turn at different speeds while
going around corners.
(Spool
Update)
Spools are
starting to appear on trucks that are road driven. Although they
don't let the tires spin at different speeds, they do eliminate erratic
handling caused by a locker engaging and disengaging.
Here are some quick reviews of each traction
product.
ARB Air
Locker
Air-actuated
on-demand locker; the best of both worlds since it can operate in
fully-locked or fully-open modes; most expensive locker on the market.
Works well on 44s, too.
Auburn
Cone
Clutch-style
limited slip that features coil-spring pre-load for constant resistance to
differentiation; a good replacement for OE limited slips, or for use in
vehicles that see bad roads or inclement weather.
Dana
Trac-Lok
Standard
flat-plate, clutch-type limited slip; mild, streetable; appropriate for
front-axle applications; normal- to medium-size tires.
Eaton
Posi
Nicknamed
“super brute” by Moroso; limited slip built with carbon-fiber clutch
plates and available in a number of spring pre-load pressures so
differentiation resistance can be tailored to suit specific applications
(including pre-loads so aggressive they’re for drag racing
only).
Powertrax
Lock Right
Inexpensive
insertable locker; do-it-yourself install; a bit more harsh in
disengagement than new Powertrax No-Slip.
Powertrax
No-Slip
Insertable
locker with smoother operation than Lock Right; d-i-y installable, though
more expensive than Lock Right due to more sophisticated
engineering.
Powr-Lok
Originally
built by Dana and used in military Jeeps, now built by Precision Gear for
Dana 44 and 60 axle applications; four-pinion design with pre-loaded
clutches; cross-shafts have a ramp design that squeezes power on the
clutches as engine torque is delivered.
Power
Brute
Four-pinion,
two-cross-shaft unit similar to the Powr-Lok and built for import
applications.
Tractech
Detroit E-Z Locker
An insertable
locker; like the Powertrax Lock-Right in terms of function and
installation ease.
Tractech
Detroit Gearless Locker
The newest
product from Tractech is an insertable locker that uses clutches, a
steel-disc assembly and a side coupler splined to the axleshaft rather
than internal gear teeth for locker operation; the most streetable full
locker.
Tractech
Detroit Locker (also called NoSpin)
Complete-carrier-assembly unit; senses driveline power and locks
shafts together; physically the strongest unit on the market; appropriate
for any application from recreation to competition.
Tractech
Detroit Truetrac
All-gear,
torque-sensing limited slip; appropriate for front-axle
applications.
Traction
Loc
Ford Motor
Company’s version of the Dana Trac-Lok.
Zexel Torsen
All-gear, torque-sensing differential; similar to Truetrac but has beefier
case, more aggressive teeth, and a higher torque bias so it reacts
quicker.
Resource FOURWHEELER Magazine
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“Avoid front-end locker
applications unless you’re rockcrawling. You’re just
gonna break parts.”
—T.C., Reider
Racing
“Running a locker in the
front axle is not an issue on the street as long as you
have hubs that unlock and the transfer case is
disengaged.”
—Andy Gerrick,
Powertrax
“Our average retail for a
Detroit Locker is $450 to $550. For an ARB it’s around
$650, plus $200 for the compressor. But you can save
money by running the wiring and air lines
yourself.”
—Chris Corbett, Randy’s Ring
& Pinion
“Installation costs depend on
where you are in the country. Here in the Detroit area,
installation in the rear axle will run about $250, $350
for the front.”
—T.C., Reider
Racing
“Call around to see what your
local shops charge for installation. Here [in Washington
state] we charge anywhere from $250 to $300 per axle.
Some shops charge more for an ARB, since they have to
drill and tap the axle [for the air lines].”
—Chris Corbett, Randy’s Ring
& Pinion
“If you’re a 10 percent
off-roader, a mechanical locker offers no more benefit
than a limited slip.”
—Chris Corbett, Randy’s Ring
& Pinion |
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“I can’t imagine going
off-road without a locker. Limited slips are
useless.”
—Andy Gerrick,
Powertrax
“As long as both tires are on
the ground, a limited slip will go through most of the
same obstacles that a locker will take you
through.”
—T.C., Reider
Racing
“The cone-style posis are
popular, but they’re non-rebuildable. Once you’ve worn
one out, they’re basically a paperweight.”
—Chris Corbett, Randy’s Ring
& Pinion
“Clutch [limited-slip] units
work best when they’re grabbing, so watch your throttle.
Too much power will overcome or burn out the clutches.
Let off the gas and let the clutches grab and do their
work.”
—T.C., Reider
Racing
“For most situations, OE
limited slips are OK, but today’s units aren’t as strong
as they were in the past. You know, back when a truck
was a truck, not a station wagon.”
—T.C., Reider
Racing
“If you’re running tall tires
check the locker’s warranty. Most companies drop their
warranty if you’re running over a 33-inch
tire.”
—T.C., Reider
Racing
“Any increase in the size of
a vehicle’s engine, tires, weight, etc., may prohibit
use of a NoSpin differential in a heretofore approved
application.”
—NoSpin/Detroit Locker sales
brochure
“If you’re running tires over
35 inches, make sure you’re buying a
full-carrier-replacement locker, especially in the
rear.”
—Chris Corbett, Randy’s Ring
& Pinion
“The Lock Right, No-Slip, and
E-Z Locker are truly no-brainers to install. Others can
be do-it-yourself if you’re mechanically able. If you’re
up to rebuilding engines, you can install a
locker.”
—Chris Corbett, Randy’s Ring
& Pinion
“Anything that requires
disassembly of the unit to get at the spider gears needs
professional assembly.”
—T.C., Reider
Racing
“I can’t imagine going
off-road without a locker. Limited slips are
useless.”
—Andy Gerrick,
Powertrax
“As long as both tires are on
the ground, a limited slip will go through most of the
same obstacles that a locker will take you
through.”
—T.C., Reider
Racing
“The cone-style posis are
popular, but they’re non-rebuildable. Once you’ve worn
one out, they’re basically a paperweight.”
—Chris Corbett, Randy’s Ring
& Pinion |
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“Clutch [limited-slip] units
work best when they’re grabbing, so watch your throttle.
Too much power will overcome or burn out the clutches.
Let off the gas and let the clutches grab and do their
work.”
—T.C., Reider
Racing
“For most situations, OE
limited slips are OK, but today’s units aren’t as strong
as they were in the past. You know, back when a truck
was a truck, not a station wagon.”
—T.C., Reider
Racing
“If you’re running tall tires
check the locker’s warranty. Most companies drop their
warranty if you’re running over a 33-inch
tire.”
—T.C., Reider
Racing
“Any increase in the size of
a vehicle’s engine, tires, weight, etc., may prohibit
use of a NoSpin differential in a heretofore approved
application.”
—NoSpin/Detroit Locker sales
brochure
“If you’re running tires over
35 inches, make sure you’re buying a
full-carrier-replacement locker, especially in the
rear.”
—Chris Corbett, Randy’s Ring
& Pinion
“The Lock Right, No-Slip, and
E-Z Locker are truly no-brainers to install. Others can
be do-it-yourself if you’re mechanically able. If you’re
up to rebuilding engines, you can install a
locker.”
—Chris Corbett, Randy’s Ring
& Pinion
“Anything that requires
disassembly of the unit to get at the spider gears needs
professional assembly.”
—T.C., Reider
Racing | | |
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