Nissan Patrol 4x4 (Africa)

Eye Russ, you're probably right. Couple this with the fact that the Patrol already has a relatively high-geared low ratio of only 2:1 (compare this for example with the fact that the older series landies had a low ratio of about 3.25:1).

Suffice to say, if I had the spare cash lying around I would have done that a long time ago already...

Peter, Russ,

Thanks your comments are helpful. Still I do not understand all the issues here.
The Lexus is very powerful on high revs. It murders sand dunes.
Also, the power is very smooth all the way through the revs range (unlike aspirated motors that peaks and then goes down at higher revs).
While being smooth though, the torque increases gradually as the revs go up, and is less than the 4.5 and 4.8 at lower revs.
So, the torque can be a little low at the lower revs, which I think is why my clutch works very hard when rock crawling (manual).

Not sure what my current factory spec ratio is (2004 GRX), but Peter you say that perhaps a ratio of say (2.6:1) would do the trick? (on 33" tires)
This is not a critically important mod for me - lower down my list. The Patrol remains a life long project...

Just to confirm, it seems that a transfer case crawler gear mod is perhaps a safer option than replacing the crown wheel and pinion? - This is given the serious amount of strain that the diffs are already subject to? Also a diff gear replacement needs to be absolutely perfectly set-up. Apparently any replacement can lead to some "humming" noise afterwards.

Thanks

Alex

Alex, the tractive effort at the contact patch is a function of all the ratios between the flaywheel and the wheel, as well as the wheel (tire and rim) radius. Effectively, you multiply all the ratios together, multiply that by the engine's torque (at the specifik revs you are interested in), and then divide that by the wheel radius to calculate how much force is available to push the car forward.

As an example, my car has a first gear ratio of 4.556:1, a low ratio of 2:1 and a diff ratio of 4.111:1. Thus the total gear ratio in 1st Low is 4.556x2x4.111=37.46:1 Now let's say I have 350N/m of torque @1500rpm and my tires are exactly 33" in diameter, I would thus have 37.46x350=13110Nm at the wheels and 13110/0.491=31283N available at the contact patches. That is 3128kg of tractive effort. In other words, assuming I have enough traction, I could just-just climb a wall at 1500rpm. But ideally I want to be crawling at 600rpm, and there I have less than half that torque, and you probably have even less. Speed can be calculated in the same manner, and is perhaps more important here, as the slower you go the more control you have.

The crux, however, is this: if you are happy with the on-road performance of your car with your chosen tires, then there would be no need to change the diff ratios. A change in transfer case ratios would thus be simpler and cheaper.

Please note that what we are discussing here is a change in transfer case ratios, not a crawler gear. A crawler gear is actually another 2-speed gearbox fitted between the normal gearbox and the transfer case. It gives you another whole set of ratios to play with, and a third gear lever.

agreed,

Crawler gears seem to be on the way out though too, with most opting for a simple transfer case reduction gear change instead. I know Marlin Crawler gears was the name to have many years ago, with some guys ordering for the old SFA hilux ages ago.

As peter says, if your vehicle pulls well with the tyres you on now and you happy (ie: 2wd around town and highway), then there would be no need to change the diff ratio.

However your lexus seems to struggle on the steep rocky inclines where very low speed and control is needed. Obviously you will be working your clutch alot harder to try and find the sweet spot ( a balance between your peak torque and low speed), but with that lexus torque curve you probably find that the revs will be to high which leads to wheel slip and an uncontrolled or wild ascent . This is where people find the transfer case reduction comes in handy. 43% (biggest reduction) or 85% (smallest reduction) reduction gears (sounds more radical than it actually is though) , are your options, and would remedy this issue.

Werf Otter , a member here has 85% low range transfer gears on his patrol (see link below for details)
http://www.patrol4x4.co.za/viewtopic.php?f=43&t=1280

Russ.

Peter Connan wrote: the older series landies had a low ratio of about 3.25:1).

Indeed, on the farm we had 3 x 45 series Cruisers and 1 Series 3 LR , we used these vehicle as pure workhorses and didn't spare them for anything.

The LR always broke down but the low gearing was insane. I had to get them up into a barn with a vertical concrete step hight more than half the wheel hight. The 45 cruisers needed a tyre to be put down infront to try and make it, but the series LR surprised all of us and climbed the step basically vertically , and it only had the 2.25Lt motor! just shows you.

Thanks guys

The car cruises very well on the highway, so I will stear clear from changing the diffs.

Simpler sounds more reliable. I.e. a change in transfer case ratios rather than a crawler gear.

Would it be required to change the diff ration's on a 4.5 if wanting to fit 35" tyres? What is the standard diff ratio that the 4.5 come out with?
As far as I know (from what I have read), not all model patrol's came out with the same diff ratio's?
What is the ratio for the 4.2 pickup?

SJC wrote:Would it be required to change the diff ration's on a 4.5 if wanting to fit 35" tyres? What is the standard diff ratio that the 4.5 come out with?
As far as I know (from what I have read), not all model patrol's came out with the same diff ratio's?
What is the ratio for the 4.2 pickup?

P.S. I read that the recommended ratio for fitting 35" tyres would be about 4.6 ?:think:
The 2.8 diesel gu & gq came out with a 4.6 ratio diff - does this mean that if having to up the ratio to fit 35" tyres, I must get hold of a 2.8's diff?

Diff ratio info here: http://www.marks4wd.com/diff-ratio-information

I suspect the 2.8's probably all have H233B diffs. I also suspect your 4.5 has a H260 rear diff, and i know the bakkie has.

I think both your cars will be very sluggish with 35's and standard gearing.

How difficult($) is it to change diff ratios?