Low Range

would say it's more likely to be fifth gear in the gearbox that will need replacing as it's an inherently weak gear and shouldn't be subject to the huge torque produced in low range. I would recommend only using low when absolutely necessary - high range results in less stress on the drivetrain and produces better fuel economy...unless you're labouring excessively of course...

The low range actually roughly halves the torque load on the 5th gear, all the torque multiplication occurs at the transfer gearset not in the transmission. The reason it is not suggested that you use 5th is that 4th is usually a "straight through" locked mainshaft 1:1 ratio and is inherently stronger than any other gear, therefore thought to be more reliable. Notwithstanding that, the 5th gearset is usually the weakest of all of them and is better avoided in anything but flat level ground in 2WD.

Low range can give you an edge in controllability in some instances and better engine braking as well.

Gary,

Doesnt the torque multiplication occur thru the application of the gearing, i.e 300Nm at the flywheel via a 1:10 gearing gives 3000Nm at the back of the gear box, if 5th gear is at the back of the gear box then it'd get a lot of that extra torque. I ony use low range to 4th gear also due to the "straightthruness" of the gearset

You choose your gears for whatever you are doing, personally I choose high or low back and forth depending on what the track is looking like, mind you once i went down this hill in 4H should have DEFINITELY been 4L silly bugger!, but 4H still turns all the wheels and is easier on the whole vehicleLaterally Literal
Seriously Cerebral

"Doesnt the torque multiplication occur thru the application of the gearing, i.e 300Nm at the flywheel via a 1:10 gearing gives 3000Nm at the back of the gear box, if 5th gear is at the back of the gear box then it'd get a lot of that extra torque. I ony use low range to 4th gear also due to the "straightthruness" of the gearset".

Yes it does, but through each succesive gearset. For example consider a gearbox with 1st gear of 3:1, 4th gear 1:1, and a transfer case high of 1:1 and low of 2.5: 1, and consider points A input to gearbox, B output of gearbox/input of tcase , and C output of tcase.

With 200 Nm at point A:
In 1st high there would be 600 Nm at point B and point C,
In 4th high there would be 200 Nm at point B and point C.

In 1st low there would be 600 Nm at point B and 1500 Nm at point C,
In 4th Low there would be 200 Nm at point B and 500 Nm at point C.

"... but 4H still turns all the wheels and is easier on the whole vehicle...".

Not really.

From looking at the above example it is clear that in 1st high both the gearbox and tcase are stressed to 600 Nm, wheras in the 4th low example, the gearbox only has 200 Nm going through it and the tcase has 500Nm (roughly equal in reality due to friction losses). The tcase is designed for continuous running in low ratio whears the gearbox is designed with a definite duty cycle to get to 4th gear (ie not "live" in 1st, 2nd or, 3rd).

I think there is also a little bit of confusion about "...the back of the gearbox...". This refers to the output shaft and not to the physical location (most 5th gearset are located physically at the rear but in mechanical reality are driven by the same shaft that drives all the other gears). The 5th gearset will recieve the same 200 Nm (in my example) input toque as any of the other gearset would, but it would produce LESS torque output ie. 160 Nm with a 20% overdrive at our point B.

Not criticism, just education......... :-))

"From looking at the above example it is clear that in 1st high both the gearbox and tcase are stressed to 600 Nm, wheras in the 4th low example, the gearbox only has 200 Nm going through it and the tcase has 500Nm (roughly equal in reality due to friction losses)...."

Clarification: "...roughly equal in reality..." was referring to 500 Nm vs 600 Nm.

I'm the same Moose.

Leroy

Hi Paul

Forgive my ignorance - I've only ever used low range for extra grunt pulling a boat up a slippery boat ramp / crossing a creek etc.

What advantages have you found in using low range for boggy / slippy / sandy situations? Is it not simply a questions of switching the diff lock on?

Rgds

Rob

the diff lock you refer to is only the centre diff, not a cross axle diffLaterally Literal
Seriously Cerebral

G'day Col,
Hows the FnFNQ treating you.

I use low range off road if and when it suits- the GQ Gbox is built like a brick outhouse and used sensibly will last forever. Have always used whatever is the most sensible gear for the situation which sometimes favours low ratio and sometimes high. Have also always used 5th gear as much as any other with no dramas in 13 years- probably a third of my kays have been towing and much of that in 5th gear!!