Twin·Traction Differential

GOODTRACTION

•DELIVERS POWER~HERE IT~ NEEDED

The Twin-Traction differential rear axle nowava i Iab le on 2E5, 2E6, and 2E7 model trucks ful-fills a long standing need for a differentialwhich prevents a vehicle from oecoatn g in-moOile when one wheel loses its traction.

Its unique design provides several distinc-tive advantages over the conventional typedifferential assembly. The main feature ofthis differential is that it supplies a greaterpercentage of torque to the wheel with bettertraction and still furnishes to the wheel withthe poorer traction as much torque as it isable to absorO under the circumstances.

In the conventional differential, the wheeleasiest to turn receives the power. Therefore,.when traction conditions under the rear wheelsare not the same, the driving force is limitedby the wheel with the poorer traction (easiestto turn) even though one wheel is on good trac-tion surface. In the Twin-Traction differen-

tial, power is prOVided also to the wheel onbetter traction surface and in this way thedriving force gets the advantage of the bettertraction surface.

The Twin-Traction differential, unlike thefull locking type differential, does not permitshock loads or full engine torque to be trans-mitted to one axle shaft. It provides power toboth rear Wheels ana maintains the differentialaction that is necessary when the vehicle isturning a corner to permit the outer wheel toturn taster than the inner wheel.

The Twin-Traction differential provides ad-ditional vehicle safety and staOility duringhigh-speed driving. It prevents theel spinningand sudden shock loads due to wheel bounce overrough roads or non-uniform road conditions suchas ice or snow spots, wet and dry pavement,sand and gravel, and one wheel running off thepavetlent.

G 00 0 C REA T E S CUSTOMER GOO 0 L LS E R V C EW"------- .. -.-----

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No. 311 SERVICE BULLETIN

With a conventional differential. when arear wheel Is thrown into the air by a bump androad contact Is broken. the wheel spins andrapidly gains momentum. As It returns intoContact with the road. the sudden shock ofcontact causes the vehlcle to swerve. Withthe Twin-Traction differential. the wheel hit-ting the bump cannot spin and gain momentum;consequently. sudden wheel stoppage to cause

.swerVing Is not present. This is also trueWhen the wheel hits a p a t cn of lee. snow. orwet pave men t; 1t does not spin and thereby pre-vents swerVing of the vehlcle when the wheelreturns to the dry pavesent. In a situationwhere one wheel drops off the pavement onto asoft Shoulder, the wheelan the pavement con-tinues to drlve and the wbeel on the shoulderdoes not spin. Here again swerVing Is preventedwhen the wheel comes back on the pavement.

The differential assembly consists or twocase halves (1 and 7, Fig. I), two cross pins(5). dirferentlal pinions (4). bevel side gears(3), clutch rings (2). and axle s na rt thrustblock (6).

The cross pins are made with a movable jointat the center to permit each one to move inde-pendently while in continuous engagement. Thepin ends are lachined In the form of a V (seeFig. 2) and a s t a i Ia r V is machined in each

MAR C H I 9 5 6

FI G.2

1. CROSS PINS

case half to prOVide a ramped cam surrace.clutCh ring is ritted over each bevel sideand mates with a cone surrace machined Inhalf of the difrerential case.

Thegeareach

As the vehicle is put in motion, the drivingrorce moves the cross pins (2, Fig. 3) up the rampor the cam surrace (1). applying a load to thec Iutcn rings (4) and restricts turning of the dH-ferential through the frlction or the clutCh ringon its mating surface (5) in the differential case.

2

1. CASE HALF

2. CLUTCH RINGS

3. BEVEL SI DE GEARS

FI G. 14. DIFFERENTIAL PINIONS

5. CROSS PINS

6. THRUST BLOCK

7. CASE HALF

8. CASE SCREWS

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SE R VI C E BULLETIN

f1G.3

1. RAMP SURfACE

2. CROSS PINS

3. DIFFERENTIAL PINIONS

4. CLUTCH RINGS

Tnis provides a torque ratio between the axlesnafts which is based on the amount of friction inthe differential and the amount of load that isbeing applied to tne difrerential.

When turning a corner, this process is in effectpartially reversed. The differential gears become-a planetary gear set, with tne gear on the insideof tne curVe becoming the fixed gear of the plane-tary. Tne outer gear of the planetary overruns astne outside wheel on the curve has a further dis-tance to travel. With the outer gear overrunningand the inner gear fixed, the differential pinions(3, Fig. 4) are caused to rotate, but since tneyare restricted by tne fixed gear, they must firstmove the cross pins (2) baCk down the carn sur-race (1) relieVing the thrust load of the clutChring on its mating surface in the differential case.Thus wrlen turning the corner, the o rrrerentia t , forall practical purposes, is Similar to a conventionaldifferential and the wheels are free to rotate atdifferent speedS.

The engagement of the clutch rings in tne !Win-_ Traction differential prOVides many features that

are not common in other types of lOCking dif-ferentials. On straight driving, the clutchrings are engaged and prevent momentary spinningof the wheels when leaVing the road or whenencountering poor traction. In turning thecorner, the load is relieved from the clutch

- su~faces so that wear is reduced to a minimum.

Servicing Twin-Traction DifferentialThe TWin-Traction differential is entirely

new in deSign and ~ertain characteristics lUStbe taken into consideration. Under averagedriVing conditions SUCh as straight ahead,

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No. SII-

FI G. 4

5. CLUTCH RING MATING SURFACE

reverse, extreme right and left turns, theoperation will be tne same as with the standarddifferential. However, a 11 ttle more cacx i asnmay be noticed due to tne lateral movement ofthe differential cross pins. In addition,a Slight Chatter may occur under surge torque

_ with one wheel on a slippery surface. Theseconditions are considered normal.

Should ditficulty occur requiring the re-moval and se rv Ic In g o r tne unit, the differen-tial ~ust be replaced as an assembly. Indivi-dual parts are not available. For service, theassembly can be order~d through your partsdepot as Part No. 1687190 tor the 4.09 and 4.27ratios, and Part No.1687191 tor the 3.73 ratio.It will be furnished less ring gear and sidebearings. The 2E Series Twin-Traction axlecannot be used in prior production models.

Service instructions for tne removal and installa-tion of the u trrerenr rai case assembly and adjus t-ments of the ring gear and pinion are the same asthose described on pages 5 tnrougn 8 of the RearAxle Section of the 2E Series Trucks Shop Manual.

At the time of production, the rear axle 1sfilled with an Elco 28 Hypoid type lubricant.Should it be necessary to add or change thelubricant, use only S.A.E. No.90 n y p o Id typeLub r Lc a n t with a s u i p n u r vc m or me-ueac nese ,

CAUTION -- Do no~ attempt to spin a rearwheel under power with a jaCk under only ones1de; both wheels must be Clear or the ground.If one wheel remains in contact with the ground,there is a possibility that when spinning theother wheel, friction on the differentialClutch rtngs may set the vehicle 1n motion.

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No. 311 S E R V ICE BULLETINI

A P R I L 1 956

STUDEBAKER TRANSTAR TRUCK SERVICE TOPICSvs ENGINE

GOOD SERVICE DOESN'T COST --IT PAYS!

o 0

Many a truck Jockey fancies hilself to be a budding geniuswhen it cOles to tuning up the engine. Notions regardingvalve adjustment, 19nition tiling, carburetor settings to give

.' .more power, are a dime a dozen.

The really smart cooky will learn what the factory specs areand latch onto them as if they were his own brain child. Forthis smart Joe we are listing the tune-up dope for readyreference. It's a good idea to carry it with you.

Spark plug gap .035" Cylinder head capscrew torqueSet ignition exactly on mark' 60 !5 lbs.Ignition point gap minimum .013" Valve tappet clearance .026"Ca. dwell 28-340 Engine idle speed 550-600 RPM

Spark plug. Tighten to 25-30lb. ft. torque.

Here are soae Do's and Dont's that should be a part of anyeng1ne tune-up. If you know them all, good. If not, it willpay you to make them a part of the program because they areoften the difference between a slick running engine and onethat doesn't run so good. .~

If you have the spark plugs out and intend toreuse them, always file the end of the centerelectrode and the inner side of the groundelectrode until they are bright and clean.

Always use new gaskets on spark plugs.

Be sure gasket surface on cylinder head isclean.

T1ghten spark plugs to recommended torque sothat heat w111 be transferred to cooling system.

When installing ignition points be sure of thegap. Use a CLean feeler gage. Set at not lessthan .013" or more than .015".

Use a spring scale to set the ignition pointcontact arm spring to 19-24 oz. Properlyadjusted spring tension prolongs point life andaids 1n preventing high speed miss.

When setting the ignition timing, always dis-connect the spark modifier and then set timingexactly on the .ark.

Be sure the manual Choke works freely. Thechoke valve should be wide open with the knobpushed in.

DOH ' TDon't forget to check the heat riser valve.This gadget, when not working properlY, canreally affect gas mileage.

Don't forget to check the carDuretor throttlefor fUll opening by the accelerator pedalafter a cylinder head has been removed.

Don't tighten the valve cover retaining nutstoo tight. The cover can be distorted causing apermanent oil Jeak. Just snug them up.

Don't forget to clean the fuel pump bOWl.

Don't wait ror any specified mileage to cleanthe air filter. After each run take the coveroff and reel the amount or sediment in thebottom or the cleaner. If you get a gob ordirt on your !inger, clean the air cleaner outright then.Don't monkey with the carburetor idling mixtureadjusting screws unless you have tachometer orvacuum gage to tell you when the best .ixtureis reached.

General Service DepartmentStudebaker DivisionSTUDEBAKER-PACKARD CORPORATIONSouth Bend 27, Indiana

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