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followingchoicesisselectedwhentheTCMisprogrammedbythevehicle

OEM:

•StandardPreselects–downshiftsoccursotheenginespeedafterthe

shiftisapproximately300rpmabovetheenginegovernedspeed

•LowPreselects–downshiftsoccursotheenginespeedaftertheshift

isapproximately150rpmabovetheenginegovernedspeed

4.2.2.3ENGINEBRAKEOREXHAUSTBRAKEOPERATION

WhentheTCMdetectstheenginebrakeisenabled,itcommandsuseof

apreselectshiftscheduleinordertoenhanceenginebrakeperformance.

ThedefaultspeedsfortheseshiftsareknownastheAlternateEngineBrake

Preselects.

•AlternateEngineBrakePreselects–downshiftsoccuratengine

speedsapproximatelymidwaybetween1000rpmandtheStandard

Preselectsforyourtransmissionmodel

Asanoption,thepreselectshiftpointsduringenginebrakeoperationcanbe

speciedtobethesamescheduleselectedwhentheTCMisprogrammedby

thevehicleOEMfornon-enginebrakeoperation:

•StandardPreselects–downshiftsoccursotheenginespeedafterthe

shiftisapproximately300rpmabovetheenginegovernedspeed

•LowPreselects–downshiftsoccursotheenginespeedaftertheshift

isapproximately150rpmabovetheenginegovernedspeed

NOTE:SpecifyStandardorLowPreselectswhentheTCMis

programmed.

Thepreselectschedulechosenabovewillbeactivatedfordownshiftsthat

occurwhiletheenginebrakeisactiveanduntiloperationinaspeciedgear

isreached.ThisspeciedgearistheEngineBrakePreselectRangeCMC

thatisprogrammableusingAllisonDOC

.IfthisCMCissettoavaluehigher

than2(SecondRange),thendownshiftsfromtheEngineBrakePreselect

Rangeto2(SecondRange)willbemadeasstandard(non-enginebrake)

closedthrottledownshifts.Additionally,iftheTCMisprogrammedtomake

enginebrakepreselectdownshiftsatStandardPreselectsorLowPreselects

speeds,downshiftsbetweentheEngineBrakePreselectedRangetoaneven

lowergearcanbespeciedtousetheAlternateEngineBrakePreselect

downshiftspeeds.Thelowestgeartousethisdownshiftscheduleisalsoa

CMC(AlternateEngineBrakePreselectRange).Ifthisoptionisspeciedand

theAlternateEngineBrakePreselectRangeCMCishigherthan2(Second

Allison Transmission 3000 User Manual

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