tow VE­HI­CLE trAns­MIs­sIons

Choos­ing the right one for you

Camper Trailer Australia - - CONTENTS - WORDS PHILIP LORD AND PIcs PHILIP LORD AND MATT FEHLBERG

When you are tow­ing a cam­per trailer, you want to be con­fi­dent that your tow ve­hi­cle is up to the job. Not so long ago, the man­ual trans­mis­sion was con­sid­ered, gen­er­ally speak­ing, as the best trans­mis­sion for this pur­pose. In 4WD ap­pli­ca­tions, in par­tic­u­lar, they were al­most a truck trans­mis­sion, in­tended to cope with the rigours of hard-core of­froad­ing and com­mer­cial use, where the man­u­fac­tur­ers built in a high thresh­old for abuse.

Au­to­matic trans­mis­sions were al­most an af­ter­thought – they were, in the main, con­sid­ered a town ve­hi­cle choice, or fit­ted to a lux­ury ve­hi­cle. Not all were built to cope with the strain of con­stant high-load sit­u­a­tions, such as tow­ing a fully-equipped cam­per trailer.

But au­to­mat­ics have come a long way in their so­phis­ti­ca­tion and abil­ity to cope with heavy loads. The fact is, out­side of the Euro­pean and the UK mar­kets (and base com­mer­cial 4WD ute ap­pli­ca­tions gen­er­ally), the au­to­matic trans­mis­sion has be­come more pop­u­lar than man­u­als. Premium SUVs now only of­fer au­to­matic, as is the case with Mit­subishi’s premium one-tonne ute, the Tri­ton Ex­ceed. While all other one-tonne utes of­fer au­to­matic trans­mis­sion as an op­tion, Mazda says that 55 per cent of buy­ers pre­fer auto across its en­tire BT-50 ute range.

Au­to­mat­ics are not only more pop­u­lar, they are the bet­ter trans­mis­sion choice when tow­ing. Tow­ing a mod­ern cam­per trailer takes a lot of con­cen­tra­tion and hav­ing one less thing to worry about – chang­ing gears – can only be a good thing. They are also much quicker to change gears, es­pe­cially in a 4WD, where

the en­gi­neers have given pri­or­ity to gear strength over light, fast gear changes.

That trans­lates to much bet­ter progress in those sit­u­a­tions where you want to keep up mo­men­tum. When climb­ing a steep hill and los­ing mo­men­tum, you want to be able to get into a lower ra­tio quickly so that you can al­low the engine to give its best in the peak torque band.

Down­shift­ing in a man­ual ve­hi­cle can lose pre­cious sec­onds – and there­fore mo­men­tum – that you can’t af­ford to lose.

The in­creas­ingly so­phis­ti­cated elec­tronic su­per­vi­sion of hy­draulic au­to­matic trans­mis­sions has a lot to do with their bet­ter per­for­mance and abil­ity to han­dling heavy-duty tow­ing. Most au­tos can now sense heavy-haul­ing sit­u­a­tions and hold lower gears for longer and down­shift more quickly. Oth­ers have a ‘sport’ mode that does the same thing. Man­ual-mode has be­come more com­mon, too, al­low­ing the driver to move the gear se­lec­tor over to a spring-loaded tog­gle po­si­tion and change gears man­u­ally by sim­ply flick­ing the lever for­wards or back­wards. Oth­ers have taken this one step fur­ther, bor­row­ing from F1 the steer­ing-mounted pad­dle shifters, mak­ing man­ual gearshifts in an au­to­matic even eas­ier.

The big­gest prob­lem I hear cam­per trailer en­thu­si­asts wor­ried about (with auto or man­ual)

“An au­to­matic is also eas­ier to ap­ply torque from a stand­still on slip­pery sur­faces”

is if, or when, you can use over­drive when tow­ing. Be­cause the trans­mis­sion in­put shaft is turn­ing more slowly than the out­put shaft, there’s the con­cern that the trans­mis­sion is un­der enor­mous load and more prone to fail­ure.

This is true for a man­ual trans­mis­sion or ear­lier au­tos that did not have the ‘elec­tronic brain’ to sense heavy load con­di­tions.

You can still use over­drive, but it takes me­chan­i­cal sym­pa­thy on the driver’s part. You have to only use it spar­ingly, in light load or no load con­di­tions. So, when tour­ing on the plains, where you can feel there’s lit­tle ac­cel­er­a­tor in­put re­quired to main­tain speed, or when trav­el­ling down­hill, over­drive is fine.

On the plains, most ve­hi­cles tow­ing a hy­brid van or gen­er­ously-equipped cam­per trailer won’t be happy in over­drive – there’s sim­ply too much load – and when head­ing down­hill you have to be se­lec­tive. There’s no point drop­ping into over­drive when it’s a blus­tery day, the road is un­even and push­ing the rig around, or if you have traf­fic ahead. In those in­stances, a lower gear is al­ways bet­ter, so that you can ac­cel­er­ate quickly out of trou­ble or use engine brak­ing to help slow the rig down.

As for mod­ern au­tos, they do this for you.

AUTO BEN­E­FITS

The Jeep Chero­kee and Grand Chero­kee both have over­drives in their stan­dard hy­draulic au­to­matic trans­mis­sions. The Chero­kee has over­driven gears from sixth through to ninth gear, while the Grand Chero­kee’s top two gears in its eight-speed auto are over­drives.

We asked Alan Swan­son, se­nior man­ager of prod­uct strat­egy at Fiat Chrysler Au­to­mo­biles Aus­tralia, how these two ve­hi­cles op­er­ate un­der heavy load con­di­tions, such as tow­ing. He said, “The gear­box in the Chero­kee and Grand Chero­kee will de­tect a load, and select a gear au­to­mat­i­cally. So if the most ef­fi­cient gear is a higher gear, then it will select it, and if it is lower, it will select a lower gear. Most Jeep ve­hi­cles are also equipped with a trans­mis­sion tem­per­a­ture read-out as stan­dard, which is there to show you how the trans­mis­sion is per­form­ing, and will warn you if it is ever in dan­ger of over­heat­ing”.

This ap­plies to most mod­ern au­to­mat­ics and while many don’t have the real-time trans­mis­sion tem­per­a­ture read-out the Jeeps have, most at least have a trans­mis­sion tem­per­a­ture warn­ing light if they’re get­ting too hot.

If you’re tow­ing offroad on un­even ground, hav­ing an au­to­matic trans­mis­sion is bet­ter, too. Au­to­matic trans­mis­sions give the driver more con­trol in pre­car­i­ous driv­ing sit­u­a­tions, such as in soft sand or mud, which is crit­i­cal when you’re haul­ing a heavy load. In these cir­cum­stances, you might find that the speedy down­shift of an au­to­matic trans­mis­sion al­lows you to keep up mo­men­tum that would eas­ily be lost if driv­ing with a man­ual. An au­to­matic is also eas­ier to ap­ply torque from a stand­still on slip­pery sur­faces than a man­ual trans­mis­sion ve­hi­cle.

Gen­er­ally speak­ing, there is a price to be paid for the au­to­matic’s ease of use.

Have a look at the of­fi­cial fuel con­sump­tion fig­ures and you’ll of­ten see that an au­to­matic

ver­sion will be thirstier than the man­ual model of the same car. Yet the grow­ing num­ber of ra­tios, smarter elec­tron­ics and, in par­tic­u­lar, the lock-up torque con­verter has made the gap be­tween man­ual and auto fuel con­sump­tion much nar­rower. Power loss re­sult­ing from slip­page of the clutches in the trans­mis­sion and the torque con­verter are an in­her­ent bar­rier for the hy­draulic au­to­matic match­ing or bet­ter­ing the fuel fig­ures of a man­ual.

Au­to­mat­ics also cost more to buy (where they’re an op­tion) and ac­cel­er­a­tion can be more blunted than a man­ual, too.

TRANS­MIS­SION TYPES

Mud­dy­ing the waters is the clutch-less man­ual – also called an au­to­mated man­ual. Though rarely seen in heavy-duty tow ve­hi­cles, these trans­mis­sions change gears us­ing an elec­tro-me­chan­i­cal setup. They are usu­ally a con­ven­tional man­ual trans­mis­sion, but with an elec­tronic se­lec­tor mech­a­nism and clutch ac­tu­a­tor. As with the man­ual-mode hy­draulic au­tos, the driver can ei­ther shift gears ‘man­u­ally’ (but with­out the need for a clutch pedal) or let the trans­mis­sion do the job.

An­other va­ri­ety of trans­mis­sion is Con­stantly Vari­able Trans­mis­sion (CVT). While quite dated in prin­ci­ple, man­u­fac­tur­ers have taken to the CVT for its abil­ity to make the most of an engine’s ef­fi­ciency po­ten­tial.

The guts of the CVT is two shafts, one con­i­cal in shape, with a band run­ning from one to the other. As the band is made to change po­si­tion on the con­i­cal shaft, the ra­tio be­tween the in­put and out­put shafts changes. While CVTs are get­ting bet­ter, they’re still not used in heavy-duty tow­ing ve­hi­cles, as they can’t quite han­dle these high-load sit­u­a­tions.

One item that many au­to­matic trans­mis­sions ben­e­fit from is an ad­di­tional air-to-oil trans­mis­sion fluid cooler. Some man­u­fac­tur­ers spec­ify the fit­ment of such a cooler as part of their heavy-duty tow­ing pack­age, while other man­u­fac­tur­ers have faith in the orig­i­nal de­sign.

Even though some man­u­fac­tur­ers claim their auto trans­mis­sions are ‘sealed for life’, don’t pay at­ten­tion to that if you are tow­ing reg­u­larly with your ve­hi­cle. A fluid and fil­ter change ev­ery 50,000-60,000km is a good idea. Make sure that the me­chanic uses the cor­rect fluid for your ve­hi­cle, though, as some trans­mis­sions re­quire a spe­cific fluid and if you use some­thing else you may find that your trans­mis­sion fails be­cause of it.

The mod­ern au­to­matic trans­mis­sion is the way to go for heavy-duty tow­ing. Most of­ten, it’s the only way you can go, and you and I are bet­ter for it.

CloCk­wise from top: Ap­ply­ing torque from a stand­still on slip­pery sur­faces with a cam­per in tow is eas­ier with an au­to­matic trans­mis­sion; Auto trans­mis­sion fluid and fil­ter must be changed on a reg­u­lar ba­sis when tow­ing; Euro­peans still pre­fer a man­ual trans­mis­sion when tow­ing.

Top lefT: Most mod­ern au­to­mat­ics have a man­ual mode. Above: Au­to­mat­ics like this Kia Sorento pro­vide a hastier down­shift com­pared to man­u­als to help main­tain vi­tal mo­men­tum.

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