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CLARK DIFFERENTIALS

Theory of Operation

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THE 01FFERENTIAL

The purpose of a differential is to provideequal power to both wheels during normaloperation, ...

The parts that make up a differential include:

1. The Pinion Drive Gear

and to allow the wheels to rotate at differentspeedswhife turning the machine.

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2. The Ring Gear (or Crown Gear)

4. "Spider Assembly" which includes the crossand pinion gears

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3. CaseHalves •

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5. Side Gears

A. Splined on the inside diameter to acceptthe splined ends on the axle shafts .

7. The carrier housing, bolted to the axlehousing.

6. Thrust Washers which fit between the sidegears and the case halves.

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This is how the standard differential works whenthe machine is moving in a straight line. The ringgear is bolted to the case half, and the crossassembly is clamped into the case halves.

The pinion cross gears are forced to revolve withthe cross, but are free to rotate on their ownaxis, when required.

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Therefore, as the pinion gear turns, it rotates thering gear which causes the entire differentialassembly to turn as one unit.

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When the machine is operating in a straight line,both wheels have equal traction, and bothwheels" A" and "B" travel at the same speed.The complete assembly turns as one unit.

The original intention was to allow one wheel torotate faster than the other. But when the fasterrotating or slipping wheel "A" turns easier thanthe opposite wheel "B", it begins the differentialaction, and allows the available power to be usedup by the slipping wheel. This happens anytimeone wheel can rotate easier than the other .

As the machine operates in a turn, the insidewheel "B" does not want to turn as fast as whenit traveled in a straight line. The outside wheel"A" wants to speed up and turn faster because ithas a greater distance to travel.

The side gears are attached to the axle shafts,and must turn at the same speed as the wheel towhich they are attached. The side gears can slipon the thrust washers. Because the side gearscontact the pinion cross gears, when they rotateat different speeds, it causes the pinion crossgears to rotate on their own axis. The gearassembly has now stopped turning as a unit as itdid when both wheels were traveling at the samespeed. This is how a standard differential works.

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To improve the differential, a new unit wasdeveloped called the Limited Slip. The followingexplains the operation of the limited slip dif-ferential.

The two side gears are splined on the outerdiameter as well as on the inner diameter.

Two clutch packs with clutch plates internallyand externally splined are added. These clutchpacks replace the thrust washers that were usedin the standard differential. One clutch pack isput in each of the differential case halves.

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The case halves have internally cast splines. •

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The case halves are bolted together so that theclutch plates are pressed against each other .

When both wheels have equal traction, wheel"A" turns at the same speed as wheel "8" andthe entire packs "C" and "D" simply ride be-tween the side gear and housing with no effect .

The friction grip of the clutch discs has to beovercome before the wheels are allowed to turnat different speeds.

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As the machine turns a corner and both wheelshave equal traction, the inside wheel "8" doesnot want to travel as fast. The outside wheel"A", pushed by the swing action of the turn,wants to speed up. Enough force must be ex-erted to cause the clutch packs "C" and "D" toslip so that the standard differential gearing willtake effect. This is very similar to the originaldifferential, but limits the wheel slippage.

However, in some applications, it may be im-portant not to have any power loss in eitherwheel. This is the reason for the No-Spin Dif-ferential.

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This assembly allows the wheels to turn at dif-ferent speeds, with the clutch packs transferringsome power to both wheels at all times. Whenone wheel "A" looses traction or begins to slip,the clutch packs will not allow it to consume allof the power but will transfer some power backto wheel "8" with the better traction. This isthe basic principal of the Limited Slip Differen-tial.

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The No-Spin Differential consists of manycommon parts used in both the standard andlimited slip differentials. The ring gear is boltedto the differential housing, and fitted togetherwith the pinion drive gear.The crossassemblyisclamped into the housing.

A snap ring fits into a groove on the inside di-ameter of the cross.

However, on the crossassembly,a key is put onthe inside diameter. This key looks like a longtooth.

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It fits into a groove on the outside diameter ofthe center cam when it is positioned inside thecross.

This slot is wider than the key and allows thecenter cam to rotate a short distance.

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The narrow slot of the center cam accommo-dates the key of the cross when assembled to-gether. •

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A driven clutch member fits on either sideof thecrossand center camassembly.

The gapbetweenthe endsof the "hold out" ringmeshes with the bottom section of the longtooth or key of the cross.

By removing the driven clutch member, therotatable "hold out" ring can be seen held inposition around the inner row of fixed clutchteeth.

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The inner row of clutch teeth on the drivenclutch members, fit between the teeth of thecenter cam. The outer row of clutch teeth sitsloose in the large gap between the teeth of thecross.

The center cam is allowed to turn a short dis-tance inside the cross at point "8".

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If the two driven clutch members are heldagainst the cross and center cam assembly, onlythe cross will move back and forth in the gapbetween the teeth of the driven clutch members.

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It is held by each driven clutch member by theinner row of teeth fitting snug into the teeth ofthe center cam at point "C".

A spring retainer sits against the flange of eachsidegear.

The return spring sits on the shoulder of eachdriven clutch member.

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To allow the splined outside diameter of the sidegear to fit into the splined inside diameter of thedriven clutch member, the spring must be com-pressed.

The carrier housing supports the pinion drivegear, ring gear, and differential assembly. This isbolted to the axle housing to complete theassembly.

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Each side gear sits in either end of the differen- •tial housing and is splined on their inside di-ameter to accept the splined ends of the axleshafts.

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•These are the No-Spin components. The No-SpinDifferential really has only a few modificationsfrom the standard and limited slip differentials.

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When the machine is traveling in a straight lineand one wheel looses traction, the positive lock-ing differential allows equal power to be deliv-ered to both wheels. This is the main advantageof this type of differential.

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When there is equal traction on both wheels, theentire housing and differential turns as a unit.The two axle shafts are locked together throughthe side gears by the two driven clutches whichare positively locked to the cross and ring gear.

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As the machine begins to turn, the outside wheel"A", pushed by the swing action of the turn, isallowed to disengage and turn faster than theinside wheel "8", to cover this longer distance inthe turn. The inside wheel "8" continues todrive the vehicle through the turn.

To understand how the outside wheel disen-gages, and turns faster than the inside wheel,consider this example. If clutch member "A" ispushed faster than clutch member "8", member"A's" inner row of teeth will try and push thecenter cam along with it. "8's" inner row ofteeth prevents the center cam from moving.

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Clutch member" A" finds it easier to push backthe return spring, and slide up the sloped teethof the center cam, than it is to push the centercam ahead. •

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As cIutch member IIA" slidesacrossthe teeth ofthe center cam,

Clutch member "A" is now held out and awayfrom the cross,as it ridesaround the "hold out"ring, free to be pushed faster than the cross isdriving clutch member "8" .

the teeth of the "hold out" ring slide out of theshoulder of the center cam.The "hold out" ringthen slides up against the key of the crossandstopsmoving asfast asclutch member "A".

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As soon as clutch member "B" returns to thesame speed as clutch member "A", the "holdout" ring will slide back into place. Both wheelswill now turn at the same speed. This is the basicprincipal of a No-Spin differential.

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The standard, limited slip, and No-Spin differen- ~.. ,ltials all do a good job depending on the work '-'application. By providing all three types, there isa differential available for all applications.

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TROUBLESHOOTING

Now here are some common problems thatcould cause a differential to fail, and reasonsforrebuilding.

In the limited slip, further failures might occurto the clutch plates.

Differential failures could occur due to ring gear,pinion gear, side gear, or bearing failures. Thesefailures would apply to all three types of dif-ferentials.

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In the No-Spin type of differential, the springcam and/or any other of the spider assemblycomponents could fail.

The disassembly of a differential is not com-plicated, but be sure to refer to the appropriateshop manual for the proper procedures and in-structions.

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All of these failures would be causedby abusiveuse, lack of/or contaminated lubricant, and/oran improper rebuild procedure. If any of thesementioned failures should occur, the evidencewill be noise in the differential. In some cases,the machine will not steer properly or maytotally lock up the differential. This soundsveryelementary, but be sure that the problem is inthe differential before attempting any disassem-bly.

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