active,theshiftpointsforupshiftsareraisedinordertoholdthetransmission
initscurrentgearandinhibitupshiftingbeyondthecurrentrange.Holdsare
activatedbyselectingthecurrentrangeoralowerrangeontheshiftselector.
CAUTION:Atypicaluseofthe"hold"featureistomaximizeengine
brakingwhenoperatingdownhill.However,inordertoprevent
over-speedingtheengine,theholdfunctionisnotinnite.Itwill
permitshiftsfromtheholdrangetothenexthigherrangeatsome
speedabovetheshiftcalibrationspeed.
4.2.2DOWNSHIFTING.Downshiftsareallowedtooccuraslongas
transmissionoutputspeedislowenoughtokeepfromover-speedingthe
engineaftercompletingthedownshift.Whenarangedownshiftismanually
selectedbytheoperator,butthetransmissionoutputspeedisdeterminedto
beabovethelimits,thetransmissionremainsintherangeeventhougha
lowerrangewasrequestedbytheoperator.Ashifttoalowerrangecanoccur
whentheoperatorappliesthevehicleservicebrakesoraretardingdevice,
suchasanexhaustbrake,enginebrake,orretarder.Thisactionreducesthe
transmissionoutputspeedwhichinturnlowersthevehiclespeed,allowing
thetransmissiontoshifttothelowerrange.
4.2.2.1PRESELECTSCHEDULEFORDOWNSHIFTS
Thepreselectdownshiftscheduleissimilartotheholdfeature.Theoperator
mayinitiatethepreselectdownshiftshiftschedulebyselectinganyforward
gearontheshiftselectorthatislowerthanthegearcurrentlyinuse.Whena
rangehasbeen"preselected"inthismanner,shiftstoandfromgearsabove
thepreselectedgearrangeoccurathigherthannormalenginespeeds.Shifts
belowthepreselectedrangearenotaffected.
Preselectdownshiftingisbenecialinmaintaininghigherenginespeed,
resultinginincreasedenginebrakingorenginebrakeperformanceduring
downhilloperationorvehicledecelerationcycles.However,preselectshifts
arepermittedonlyifanengineover-speedconditionwillnotoccurafter
completionofthedownshift.
NOTE:Preselectingduringnormaloperationmayresultinreduced
fueleconomy.
4.2.2.2NON-ENGINEBRAKEOPERATION
Twochoicesofpreselectshiftschedulesareavailableforgoverning
preselecteddownshiftsduringnormaltransmissionoperation.Oneofthe
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