Lower gearing which way to go

[frp88]

O.K my BJ74 has stock gearing 4.1 in the diffs 2.0 for the transfer so which would be the better change.

1. Diff gears cost I think about $700 correct me if I am wrong fitting I don't know.
2. transfergears about $ 2000 fitting cost don't know .

My rear gear diff gears are worn I have a lot of movement and when I put it 4 wd it is gone. So changing the diff gears to a 4.8 set would replacing the worn rear but wasting it on the front.
I use the cruiser mainly for tow our caravan hence the lower gearing questions. Is it possible to use the front gears in the rear and put the rear in the front?

With changing the transfer I would get lower final drive and low range as a free bonus. I have a PTO on it which I don't think would be a problem.

So I am asking for your point of view and costs if you have done this before.

[TheBigBoy]

WHY???

Rockcrawler reductions transfer gears are for offroad slow crawling... And 4.8 diff gears are for bigger tyres. I wouldnt be messing with your final drive gear if all you do it tow. Just look at uping the torque and power more.

[rockcrawler31]

I've just had diff gears done to help the clutch deal with 37's

4.56's were fitted (Nitro gears from locktup) at a cost of 700 for the gears and about 250 per end to fit from a GOOD reputable fitter (JMac in sydney) as long as nothing else needs replacing and you take the diffs to them already removed from the car.

Remember that lower diff gears without a tyre increase will make it rev it's tits off at 100kmh as well as a commensurate fuel increase - However it will tow easier with the multiplied torque.

If you get transfer gears, unless you get a set with a lower high range then your towing effort will be the same, since i doubt you plan on touring and towing in low range. If you get a lower high range gearset then you will have the same effect and downsides as running lower final drive gears. The only difference will be the massive initial price.

So my summation is that if you can live with the downsides of a lower final drive (higher revs and fuel) then go the diff gears since it's a cheaper initial investment, and moves the torque further down the drivetrain. It also means you could run a second set of larger tyres for normal road driving and wheeling if you wanted to have normal driving speed range.

My 2c

[hulsty]

If you only want to help with low range gearing change out the low range gears in the transfer case.

Standard low range is 1.9 ratio, grab a set of 2.3 ratio low range gears from a different model and your done. Cheap and effective, my 2.3 ratio gears came from a HJ61 auto.

[frp88]

Sorry for not giving enough info 13bt 4 speed auto with o/drive

I run 33 and just under 2000 rpm for 100 kays but when I tow the van which is a 20 foot double axle it doesn't stay in overdrive to much load. So rather then changing the pump and boost I was thinking gearing no extra strain on the drivetrain. I was hoping that someone has done 4.8 gears to see if it has made a big diffrence. Cos at the moment I am only able to get to 80-90 kays in 3 and that is about 2600 rpm.

[hulsty]

Changing the rpm when in high via the diff gears will probably start bringing the revs up to high. What rpm does it normally sit at when on 100? Max torque is around 2000rpm.

Probably better off going 3'' exhaust and more boost.

[frp88]

I done some digging around on the net and the problem is the diffrence between 3rd and o/drive 600rpm. My 13bt doesn't make enough power transfer gear reduction will only do about 140 rpm and diff ratio change will only do 300 rpm. I have a 3 inch pipe and 11psi and the pump tuned to suite.

Minimum cost of will be $1825 for reduction gears plus $1000 labour
diffs about $ 500 for each ring gear plus $1000 labour

Maybe intercooler and pump might be the go cos I don't want to go 5.29 gears as I have been told they are weaker so towing isn't the best option with these gears.

The only other option might be to get the o/drive turned off i don't know if this is possible.

[oldmate]

look at 4.3s to put the gearing close to stock with 33's. 5.29s will see you around 3000 rpm at 110kph.

4.5s will be a good compromise.

I would go 4.5 or 4.8 if the noise doesn't bother you, then look at increasing engine output.

even with lower gearing, when a hill becomes too much for 4th gear it will have to go back to 3rd, and that will mean big revs if you want to maintain 100-110kph.

Everything is a compromise.

[berad]

look at 4.3s to put the gearing close to stock with 33's. 5.29s will see you around 3000 rpm at 110kph.

4.5s will be a good compromise.

I would go 4.5 or 4.8 if the noise doesn't bother you, then look at increasing engine output.

even with lower gearing, when a hill becomes too much for 4th gear it will have to go back to 3rd, and that will mean big revs if you want to maintain 100-110kph.

Everything is a compromise.

What he said.

Possibly not an option, run 31's when towing the caravan, and get the rear diff adjusted, unless you can swap the centres yourself the price probly isnt worth it unless your renewing parts.

Hows the gearboxs temp when under the load?..

[frp88]

I was looking at the speedo very close tonight and when O/drive cam on it droped the rpm by about 1000 which I think is the big killer.

[oldmate]

Was that under load towing? the rpm difference between 3rd and overdrive shouldn't be that much. The only scenario is if you were driving it hard in 3rd, with torque converer lockup off, then it shifts into OD, and locking the torque convertor at the same time?

When was the last time you had your auto box looked at?
And what do you rekon the total weight of your van is? a 13bt should pull 2 tonne pretty easy on the flat, but being a 4 banger i'd expect it to suffer on the hills.

Have you thought about replacing the cruiser with something more powerful?

There is no replacement for displacement.