4th or 5th Gear - again

Submitted: Tuesday, May 29, 2012 at 11:37
ThreadID: 95879 Views:7377 Replies:14 FollowUps:22
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There is a consensus that when towing, 4th gear is preferable to 5th, if you want your gearbox to last.

But why is that?

I mean, if I have a ton of equipment in the trailer I should use 4th gear.

If however that equipment is in the back of vehicle then 5th gear is OK.

Is it something to do with the towing that causes the gearbox grief, rather than than the weight itself?

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Reply By: Racey - Tuesday, May 29, 2012 at 12:12

Tuesday, May 29, 2012 at 12:12
Hi Ups and Downs

It's just the total weight. Labouring in 5th gear won't be good for the gearbox or the fuel consumption. Some years ago a friend with a nissan ute blew the 5th gear twice when towing a caravan. that was a manual box. Both time it was replaced under warranty, then Nissan issued an instruction not to tow in 5th.

In an auto the same principle applies. However with the auto everything may seem OK except when the torque converter is not locked-up a lot of heat is being generated which can cause serious damage. So by towing in a lower gear everything runs freer with less heat being generated. There has been a lot of discussion about this subject on the Landcruiser owners website.

AnswerID: 487088

Follow Up By: Member - Rod N (QLD) - Tuesday, May 29, 2012 at 12:51

Tuesday, May 29, 2012 at 12:51
Kia told me the opposite of that. They instructed that I was to tow in D at all times in my Sorento, particularly uphill, because of torque converter lock-up. They say it won't lock if auto gearbox is manually operated. Downhill manual selection of lower gears can be used for engine braking.
Maybe different makers have different rules???
FollowupID: 762329

Follow Up By: Ron N - Tuesday, May 29, 2012 at 13:04

Tuesday, May 29, 2012 at 13:04
Rod - Automatics with a sprag clutch lockup mechanism in them, are effectively in "direct drive", when locked up - not overdrive - although this lockup is commonly, and incorrectly referred to, as "overdrive".
Kia were right with their info, as automatics can overheat from excessive torque converter slippage when being used in any other gear besides OD (locked up), if they're towing heavy loads.

Cheers - Ron.
FollowupID: 762330

Follow Up By: Ron N - Tuesday, May 29, 2012 at 13:11

Tuesday, May 29, 2012 at 13:11
Racey - The Nissan transmission OD gear problem is related to the length of the splines on the output shaft of the Nissan transmission, rather than the actual OD gearset.

In the early Nissan transmissions, the OD gear slid onto the output shaft via short splines that did not make contact with the full width of the OD gear.
As a result, these short splines failed with constant towing in 5th gear.
Nissan modified the transmission and installed a shaft with longer splines that make contact with the full width of the gear - and the transmission failures caused by 5th gear towing were reduced considerably.

Cheers - Ron.
FollowupID: 762331

Follow Up By: Ross M - Tuesday, May 29, 2012 at 14:15

Tuesday, May 29, 2012 at 14:15
Ron N
An auto with a lockup mechanism doesn't use a sprag clutch for that function at all. It is a hydraulic operated annular servo piston and a clutch plate mechanism, no sprag.

The lock up mechanism is inside the torque converter and not in the auto itself.
Any problem which might arise is because the clutch is little and designed to take only cruising loads and not towing trailer type loads. When they slip they quickly burn out and because they are usually only a small single plate arrangement they can't hack the pace/load.

From what he has described Racey has a manual box where 5th is overdrive, outputshaft going faster than input shaft. This design is inherently weak as the shaft for 5th and its gears aren't well supported like most designs aren't.
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Follow Up By: Racey - Tuesday, May 29, 2012 at 16:32

Tuesday, May 29, 2012 at 16:32
Ross, Actually I have a 200 series Cruiser with a 6 speed auto. 5th & 6th are overdrive gears, 4th being direct. Toyota state tow in 5th gear. I have assumed most if not 5+ speed gearboxes, 5th and above are overdrive gears. In which case the output will be faster than the input. As I said there has been a lot of discussion on the LC owners website about this. Some have come to the conclusion when towing heavy vans +2.5 ton, to tow in 4th around 90kph, even though the revs may be a little higher the toque converter locks up and economy improves. One owner with a Scanguage fitted measured the transmission temperature @ 110deg on a long uphill pull when the torque converter was't locked up. The bottom line is to treat your vehicle with respect, if you bust it, it will be expensive.

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Follow Up By: Ross M - Tuesday, May 29, 2012 at 19:45

Tuesday, May 29, 2012 at 19:45
G'day Racey
You have a 6speed auto Landcruiser but in the original thread by ups and downs it wasn't stated and I think still isn't clarified if we a re talking to him about a manual or an auto or how many forward gears is involved either.
5th was mentioned, we just assume it is the highest.

It initially read as though you had a manual vehicle.

There are lots of people commenting but none of us really know his situation because he hasn't given enough initial information.

Regarding oil temps in auto boxes, it is common for the oil in an auto to be well above the temp of the water in the radiator, so 110 deg C is quite common. After all the auto oil is fed through a heat exchanger in the radiator to dump heat into the engines water/cooling system. It couldn't do this heat transfer if the box oil was lower.

That long up hill pull you spoke of is probably done best in a lower gear converter slipping situation so the heat which may be generated is able to be dissipated by the forward movement and the fan driving extra air past the cooling system. I would think 110 degC is not hot in that situation as the engine is probably near full heat output into the radiator and the box isn't getting much beneficial cooling action at all.

Ross M
FollowupID: 762369

Follow Up By: Member - Ups and Downs - Wednesday, May 30, 2012 at 09:16

Wednesday, May 30, 2012 at 09:16
Ross (and others)

My specifics weren't given as the question relates to all vehicles, however it is a manual 5 speed Troopy. I can see now that there are other gearboxes with more choice.

The question is whether the 4th gear advice for when towing is also suggested when not towing, but having a full load.


FollowupID: 762398

Reply By: Ron N - Tuesday, May 29, 2012 at 12:59

Tuesday, May 29, 2012 at 12:59
Ups and Downs - Once you're towing a trailer, the gross weight the engine is pulling is substantially increased. The load on the entire drivetrain is increased dramatically.

In direct drive (4th gear or top gear in older vehicles without OD), the torque from the engine is being taken in a straight line through the transmission - or in some odd cases, if through a gearset, then the gears are evenly sized (i.e., a 40 tooth gear is driving an identical-diameter 40 tooth gear).
Thus the torque loading on both gears (and gear teeth) is even.
In the case of straight-through drive, as in 4th gear with most 5 speed OD transmissions, the drive is simply the input shaft (clutch shaft) and output shaft (mainshaft) locked together by evenly-sized splined teeth.

An overdrive gear uses an indirect gear set, whereby a larger gear is driving a smaller gear.
In the case of say, a .8 ratio overdrive, the drive gear is 20% bigger in diameter than the driven gear.

In the case where maximum engine torque is being transmitted through the transmission - and the vehicle is heavily loaded with a trailer and approaching gross maximum combination mass (GCM) - then the teeth on the smaller diameter output (driven) gear are being stressed considerably more, than the teeth on the larger (drive) gear.

As a result, with constant use of OD in this situation, you stand a good chance of gear tooth failure on the smaller diameter (driven) gear. By changing back to 4th you remove the highly-stressed OD driven gear from use, and revert to a direct drive coupling or ratio, where there is not the same extreme gear tooth loading in the transmission.

In lower gears, a smaller diameter gear drives a larger gear, and the loading is on the smaller driving gear (and its teeth).
Thus, in an extreme transmission load, the failure is going to be in the smaller gear. However, this type of failure is far less common, because the smaller gear is designed to take heavy tooth loading.

In the case of OD gears, the gear teeth loading on the driven gear increases rapidly and substantially, as high torque levels are encountered.

I can speak from personal experience here. I used to own a 1968 model International tandem drive tip truck in the early-to-mid 1970's. This truck had a 6 cyl Perkins driving through a 5 speed main transmission and a 3 speed auxiliary or "joey" transmission.

The 3 speed "joey" consisted of underdrive, direct drive and overdrive gear. International warned about avoiding using OD gear in the "joey", in combination with lower gears in the main transmission.
OD in the joey was always the last gear you changed up to, and the first gear to change down as soon as the engine started labouring.

I got a job hauling sand to backfill a mine. The job involved backing up a 10M high ramp to tip the load. It was a pretty steep ramp, and being young and keen, I was always "speed oriented". I was on contract, of course!
I found that I could get more speed up, and climb the ramp faster, by using OD on the "joey" in combination with reverse in the main transmission.
The truck was always overloaded, because I was on mine roads, and axle loading limits didn't apply.

I did this for about 6 mths, before I heard an almighty BANG! one day, as I was reversing up the ramp, fully loaded.
The truck stopped driving. It was obvious the drivetrain failure was in the "joey" box.

I pulled the "joey" box out and upon dis-assembly, I found the majority of the gear teeth on the smaller OD (output) gear, completely stripped.
Thus the reason for the warning from International about the proper use of OD gear was driven home to me, in the most forceful manner!

Cheers - Ron.
AnswerID: 487089

Follow Up By: Axle - Tuesday, May 29, 2012 at 20:32

Tuesday, May 29, 2012 at 20:32
Absolutley correct Ron!!,...I learnt the same way, only in the old acco tipper we had on a long run up a hill if the ol perkins picked up revs and i was in say second or third direct i would slip, her into overdrive to gain that bit of speed instead of being patient and leave it where it was or try a higher gear in the main box, many a night crawling around in the grease and dirt removing busted gearboxes, took me enough drama to learn!..lol

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Follow Up By: Madfisher - Tuesday, May 29, 2012 at 21:51

Tuesday, May 29, 2012 at 21:51
Watched a you tube video of a fella driving a two sticker, bit of and art form. he hooked his arm through the wheel and changed one stick, and the other hand on the other stick.
Where the main box and Joey synro or crash?
Its interesting today most younger blokes can not even drive a synro manual.
cheers Pete
FollowupID: 762381

Follow Up By: Ron N - Tuesday, May 29, 2012 at 22:18

Tuesday, May 29, 2012 at 22:18
Madfisher - No synchro's in those days, a truck with any synchro's at all wasn't regarded as a real truck. Picking the cog spread was your next biggest job, after getting the revs right for smooth changes.
Great old truck the old ACCO, though, I spent a lot of time in her, and she only let me down 3 times.
Once when I busted the joey, second when I stripped the worm wheel that drives the fuel injection pump, and third when I screwed off a tailshaft.

I carted up to 350 tonnes of sand a day by myself on that mine for over a year, and carted 13,000 tonnes of ore from Higginsville to the Norseman State Battery between 1972 and 1981.
Used to have to get down to 3rd underdrive in the boxes to climb those big hills just North of Norseman - and no doubt many a fully loaded Interstater abused me soundly for making him brake or have to follow me up those hills!
I never carried a radio - CB radios were for Yanks and pussies, and I wouldn't have been able to hear anything, anyway!

Used to make me spew when the Perkins was singing her heart out in 3rd underdrive at 20kmh with 13 tonnes aboard - and a Cleveland Freight Lines Mack-Muncher road train pulling 50 tonnes in doubles, would overtake me doing 85kmh, UP the hills!
Things have changed a bit nowadays! A young bloke wouldn't even drive what we drove happily!

Cheers - Ron.
FollowupID: 762386

Follow Up By: Madfisher - Wednesday, May 30, 2012 at 13:29

Wednesday, May 30, 2012 at 13:29
At work we have an Isuzu 600 Pan , which has a six speed synchro box, but 2nd is very scratchy and it changes a lot smoother with a double clutch. I was explaining this to a young bloke who was hiring it last week, next thing he bolts back into the office and asks if he could have an auto. Compared to the old 1500 inters I drove in the 70s this truck is a revlation, so quite in 6th(2000rpm at 100) it is difficult to keep it on 100, and it will pick up speed on a moderate hill in 6th.
You need a degree to operate the seat.
Never had a go at a Joey hence my interest.
Cheers Pete
FollowupID: 762415

Follow Up By: Axle - Wednesday, May 30, 2012 at 18:19

Wednesday, May 30, 2012 at 18:19
Pete, those old 1500 inters where good in their day!,... Imagine trying to run one now on the current fuel prices!...LOL.

Cheers Axle.
FollowupID: 762439

Follow Up By: Madfisher - Wednesday, May 30, 2012 at 19:23

Wednesday, May 30, 2012 at 19:23
LOL Axle , nearly 40 years ago, but I remember they did 8 to 12 mpg depending on gearing and body. Six hours to get from Sydney to bathurst. 3rd gear up any slight incline ans we only had furniture on. I remember Dawsons got a 1500 Acco with a two speed diff and a header and we thought that was great.Then they got a bedford and grafted a 308 v8 in, for its day it flew.
They also ran a 1600 long nose that was pretty well flat at 50mph.
Cheers Pete
FollowupID: 762447

Reply By: Andrew & Jen - Tuesday, May 29, 2012 at 13:32

Tuesday, May 29, 2012 at 13:32
Hullo Paul

A lot of good advice here.

What has not been addressed so far is your query about the difference in the weight being in the trailer vs in the vehicle.

There are 2 factors at play here. Given the same overall weight, the more the number of axles, the greater the rolling resistance - and hence strain on the drive train. Secondly, if you are towing a trailer or van, the greater the speed, the more drag is produced - hence strain on the drive train. This second factor also applies to modifying the shape of the vehicle, for example, by adding a roof rack and then by the frontal area and overall shape of what you put on the rack.

WRT the use of, in my case, 3rd instead of O/D, the fuel consumption is about the same and the stress is less and the gearbox (auto) temps lower.

AnswerID: 487093

Follow Up By: Member - Ups and Downs - Wednesday, May 30, 2012 at 09:20

Wednesday, May 30, 2012 at 09:20

You have answered my question. Rolling resistance and drag rather than the straightforward weight being the difference.

So, I can use 5th in a laden Troopy although sensibly drop to 4th if the engine starts to labour.

FollowupID: 762399

Follow Up By: Andrew & Jen - Wednesday, May 30, 2012 at 12:10

Wednesday, May 30, 2012 at 12:10
Hullo Paul

As one person put it, there is no slavish answer. The way the engine / car behaves tells you a lot as you drive as there is constant feedback.

For example, one of the things I pay attention to is the ability of the vehicle to accelerate at whatever speed I am cruising at. If it only slowly picks up speed, it is an indication I might need to go down a gear. But if this occurs on a slight up hill slope and I am near the top, then I just ease off a little and let it roll over the top and then pick up speed again on the other (downhill) side.

I recently installed a combination gauge that reads EGT, auto gearbox temp, boost pressure and water temp. As a consequence, I have learnt heaps about what impacts on each of these parameters because some readings have been contrary to my previous assumptions.

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Reply By: olcoolone - Tuesday, May 29, 2012 at 13:36

Tuesday, May 29, 2012 at 13:36
Maybe once upon a time it wasn't advisable, may people these days tow in an overdrive gear and don't have a problem.

Sure the overdrive gear is smaller and the torque is multiplied in that gear, so towing in overdrive under extreme load is not advisable but along a flat or slightly undulating road should not cause any issues.

For every one person who thinks it's not OK there are thirty others who don't see a problem and have towed like that for years.

It's funny how you say people think it's OK to drive in 5th gear with a ton of weight in the back but put a trailer on weighing a ton and towing in 5th becomes a no no.....

We have towed in 5th gear for years and never had a gearbox failure.

If your vehicle pulls OK in 5th gear travelling in 5th but if it is labouring drop back to 4th.

Humans are a funny creature ...... we will always blame something for causing a failure but 9 times out of 10 we have no real data to back the claim...

AnswerID: 487094

Follow Up By: Member - peter & dawn m (QLD) - Wednesday, May 30, 2012 at 15:40

Wednesday, May 30, 2012 at 15:40
It,s a great depate this towing i owned an 1988 diesel nissan patrol had a new clutch fitted in townsville original clutch had done 285 thousand k,s time to replace + they checked the gear box 5th gear had to be replaced on heading for home sth we headed to charters towers & down the gregory development rd we had been told to only use 4th gear as we were a caravan man even the grass hopper were passing us so on level areas we towed in 5th an ghanged back to 4th as soon as it started to pull .have since got a 100 series auto diesel an have fitted an temp gauge to the auto have not had the van on since fitting the gauge but hopefully very soon will take it for a shake down cruise. swampy
FollowupID: 762423

Reply By: GT Campers - Tuesday, May 29, 2012 at 13:47

Tuesday, May 29, 2012 at 13:47

4th gear (in most gearboxes) is the strongest because the gearbox input shaft is connected directly to the output shaft. There are no cogs involved.

Fifth is the often the weakest (or, more likely to fail first) because it is seeing the most load - aero, drag etc - and therefore doing the most work at highway speeds

Towing introduces even higher aero and drag loads - possibly as much as double - which is why you use more fuel when towing than with the same weight within the vehicle


AnswerID: 487095

Reply By: Ron N - Tuesday, May 29, 2012 at 14:07

Tuesday, May 29, 2012 at 14:07
The simple answer is to follow the vehicle manufacturers recommendations in the manual.
If the manufacturer tells you not to tow in 5th gear, then don't do it. If they don't mention it, you can take heart in the fact that they designed the transmission to tow in 5th OD gear at FACTORY RATED loads.

The greatest problems stems from people asking too much of engines and drivetrains.
They chip the motor, install a turbo, or overload (or do all three) - then complain when something breaks!

Overall, I've found that Jap transmissions have less margin for overloads and abuse, and are much more finely engineered, with tighter tolerances, than most American transmissions.

The Yanks build trannys with massive reserve margins of strength, and with the ability to handle trash in the oil much better. The Jap transmissions can't tolerate any water or metal debris in the oil, because they use such tight tolerances and relatively lightweight bearings.
AnswerID: 487096

Follow Up By: GT Campers - Tuesday, May 29, 2012 at 14:21

Tuesday, May 29, 2012 at 14:21
RonN, yep, but some maunufacturers won't mention NOT to tow in fitfh gear as it is seen as an admission of weakness... they simply hope that 98 percent of the vehicles they sell with towbars won't be loaded enough to become a problem during the warranty period...and those that do fail are taken care of on a case-by-case basis. Maybe!
It's a numbers game, in more ways than one!

You are right about chipping etc - and US vs Jap engineering: Japan has had a long history of stricter fuel consumption etc in its markets so everything is lighter, more efficient...and sometimes weaker
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Reply By: ross - Tuesday, May 29, 2012 at 17:46

Tuesday, May 29, 2012 at 17:46
How longs a piece of string? It depends on which model,which gearbox,what kind of terrain ,how much is in the trailer.
Other things such as the diameter of the tyres compared to the factory ones.
Too many variables for a straight yes/no answer
AnswerID: 487109

Reply By: WBS - Tuesday, May 29, 2012 at 19:06

Tuesday, May 29, 2012 at 19:06
Here's my take on this discussion. I tow in 4th gear in my 80 Series manual. Why?
Two reasons.
First, it was recommended to tow in 4th in my owners manual for my first 80 Series back in 1993. I can't find the same advice in my 1997 80 Series owners manual but figured I would stick to the original instruction.

Second. Having fitted an aftermarket turbo, snorkel & 2.5" exhaust I also fitted an EGT gauge. The gauge tells me that to tow in fifth even on reasonably flat roads causes the EGT to rise to unacceptable temperatures (450 Degrees C and above). When towing in fourth at the same speed but at higher revs the temperature remains around the 350 C. That tells me that in fifth the engine is struggling, so 4th gear it is for me.

Its that simple. I'm trying to give my engine an easier life.

AnswerID: 487116

Follow Up By: Rockape - Tuesday, May 29, 2012 at 19:39

Tuesday, May 29, 2012 at 19:39
you have got your sums right.

If someone wants to know if they can tow in a MANUAL have a look at the exploded view of the gearbox and that will tell the story with 5th gear hanging of the end waiting to be destroyed. You can do it with a big tail wind and a light foot or just roll with an undulating road.

You often will get better fuel economy in 4th than 5th. Often people change their vehicle after a certain amount of towing and don't realise the damage that has occurred in the box.

I just wish they would put a manual gearbox that resembles a truck box in a 4wd. Then again trucks are going to auto/manuals which is a great move.

I see Ron N mention an Acco with the old joey box. Thank god they are gone.

FollowupID: 762366

Reply By: Wilko (Parkes NSW) - Tuesday, May 29, 2012 at 21:26

Tuesday, May 29, 2012 at 21:26
Hi Paul,

I agree with most here and will only tow in 4th (direct drive) but cant find anywhere a definitive rule on where the cutoff point is If I carry 250 kgs, 500 kgs 750kgs, should I use 4th gear? Ive been using the If it labours then use 4th rule and its worked on my previous 4wd's.

But now Ive got the hilux, I'm worrying more (cause the hilux clutch is crap) Sorry to highjack your thread but I'd like to know.

Cheers Wilko
AnswerID: 487127

Reply By: Member - Duncs - Tuesday, May 29, 2012 at 21:57

Tuesday, May 29, 2012 at 21:57
Many years ago I was talking to a camper trailer manufacturer. He travelled all over Aus displaying his campers at shows, he always had 3 with him.

He carried one on the tray of his GQ cab chassis and towed the second one with the third upside down on top.

I had a GQ at the time and asked him about towing. He always used the full box. Would tow in 5th but as soon as the car started to slow he would change down to 4th. Usually at about 110km/h.

Now the GQ did have a truck gearbox but his advice has proven to be very good. That was 16 years ago. I have had the GU for the past 10 years and drive it the same way I did the GQ. I tow in 5th but the slightest drop in speed sees me shifting down to 4th. I don't have any fancy gauges to tell me what the engine is doing but my fuel figures tell a story. I can see when I have been lazy and sat in 5th all the way rather than shifting down.

With a 4.2 TD the temp gauge will also tell you when you are pushing it. On the Newell Highway between Coonabarabran and Narrabri sitting at the then posted speed of 110km/h in 5th the temp was slowly rising. In 4th at the same speed the temp dropped back to normal. I would never have thought that road at that speed would be a problem, but it was.

The GU has 200k on the clock and lots of that was done with about 1 to 1.1 tonne of trailer behind it. No problems whatsoever. But I listen to my car and don't stress it and I maintain my car. I reckon there is another 200k left in it and I will continue to tow in 5th.

I agree with those who say follow the manufactureirs advice and I can't mount a technical argument to oppose the mechanincs on this forum, but my experience is valid and is proven over many years. When my mates box stripped 5th I became concerned about mine. So I asked the head mechanic at the Nissan dealership. He looked at my VIN and engine numbers and said I would be Ok. On the Nissan there was a very clearly defined period which displayed problems, mine was built outside that period.

I think this is another argument that will continue as long as there are more than one person in the discussion.

AnswerID: 487134

Reply By: Geoff in SA - Wednesday, May 30, 2012 at 08:47

Wednesday, May 30, 2012 at 08:47
ahhhhh my head and eyes are hirting after all this

Maybe my choice of a big truck has solved all these issues???

AnswerID: 487148

Follow Up By: Member - Ups and Downs - Wednesday, May 30, 2012 at 22:09

Wednesday, May 30, 2012 at 22:09
You need a big truck, towing that whopping thing behind you!

FollowupID: 762463

Reply By: PJR (NSW) - Wednesday, May 30, 2012 at 10:15

Wednesday, May 30, 2012 at 10:15
I cannot understand all the kerfuffle. It is sooooo simple. It is not a blanket statement that at 100KPH you should be in "X" gear.

Use the gear that does not "labour" the motor and doesn't need maximum revs that make it pop valves nor minimum revs that would shame any corrugated road. Then the motor is not stressed and all the drive train should be well within comfortable working parameters.

Comfortable for us (4.2td) is just about 1/2 to 3/4 revs with just enough accelerator pressure to retain speed, up hill, down dale, towing and not towing, bitumen and dirt, rocks and sand etc etc etc. Depending of course on RTA laws, road and traffic conditions.

I do not believe that anyone here is stupid enough to travel at maximum valve popping revs or at minimum kangaroo hopping revs. If you have any sense at all you will know when the combination is right for your car. It's not rocket science.

AnswerID: 487156

Reply By: Member -Dodger - Wednesday, May 30, 2012 at 17:29

Wednesday, May 30, 2012 at 17:29
My 4.2td Patrol loves 2400rpm and I tow in 4th only as it is the suspect 5th gear model 2000.
I have tried the 5th gear but with over 2 ton behind at the slightest rise it will need to be changed down and by the time you change down then 3rd is required, hence I always tow in 4th and hardly ever need to change down.

I also did a fuel comparison on the flat roads and found that 4th used only .5 to 1 ltr /100k more so another reason to stick to 4th.

The old banger now has 250k on the clock and still runs good as new.

And yes I use cruise as much as I can.. Ease of driving for Me and the vehicle.

Those old 4.2 engines just keep going on and on.

I used to have a handle on life, but it broke.

Cheers Dodg.

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AnswerID: 487184

Follow Up By: Member - Keith P (NSW) - Wednesday, May 30, 2012 at 21:48

Wednesday, May 30, 2012 at 21:48
I checked this out a bit day before yesterday coming back from out west. The road I tried it on was flat n fairly straight ...no wind ...and fine and sunny (back Narromine road from Narromine to Albert)
Running along at 2800rpm with my slightly larger than normal box trailer with about 150 kilos in it (speedo reading was just under 90)...the boost gauge was hovering around the 6-7 psi mark just cruising along.
Changed up to 5th and up to 2800 revs (100kmh) and boost was sitting on 9.5-10 psi...again just cruising along.
This alone tells me that there is immediately more stress on everything using 5th gear...so I dropped back to 4th and slowed up that little bit ....and just cruised along checking out the countryside. It also seems to me that too many folks are in a ball-tearing hurry ....and maybe travelling in 4th would ease things up for them ...and maybe see more of Oz...and enjoy their trip more.
Horses for courses tho...but I know which one I prefer.

Cheers Keith
Nothin is ever the same once I own it ...........

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FollowupID: 762462

Reply By: Member - Ups and Downs - Wednesday, May 30, 2012 at 22:19

Wednesday, May 30, 2012 at 22:19
Thanks to all who contributed and I now know that towing increases the stresses on the drivetrain due to wind and rolling resistance, rather than just because of the weight involved.

After 360,00 trouble free kilometres I must be doing something right, or just lucky!

Some really useful background to understanding the situation as well as some worthwhile opinions presented.

I will continue to tow in 4th gear with the 4.2 litre manual diesel having a 5 speed gearbox.

When just having a full load in the vehicle I'll do as usual in 5th gear, of course changing down to prevent labouring.

Thanks again to all.


AnswerID: 487212

Follow Up By: Rockape - Thursday, May 31, 2012 at 06:11

Thursday, May 31, 2012 at 06:11
just a little more to think about in the extra towing load area.

We had two identical prime movers with much the same load on the trailers. The only difference was the spread on the triaxles. One could only sit a little over 90kph and could maintain 100kph with ease. After a 500k we swapped prime movers to different trailers and the result was the same. The slow truck would now sit on 100kph with ease while the faster truck now came back to 90+ kph.

The way the road was wheel rolled caused the trailer with the larger spread to pull against the prime mover in a jerking motion.

FollowupID: 762472

Follow Up By: Member - Ups and Downs - Thursday, May 31, 2012 at 08:52

Thursday, May 31, 2012 at 08:52
Thanks Rocky

Just reinforces that nothing is as simple as it appears.

I wouldn't have anticipated that the load distribution would effect the result but it makes sense thinking about it.


FollowupID: 762481

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