Drive Train Gearing Bible

Gearboxs, Transfers, Tailshafts, Diffs, axles and CVs

Re: Drive Train Gearing Bible

Postby VMN on Thu, 22 Sep 2016 9:12 +0000

I'm RodW. There is no issue running Nitro in the back and Prado in the rear. Works for me.
If you want to save money get your mates and a 27 spline flange.
Otherwise the 29 spline is stronger but I don't think it is the weakest link so not really an advantage in practice.
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Re: Drive Train Gearing Bible

Postby FAIL on Tue, 27 Sep 2016 6:15 +0000

Thanks Rod,

So it's a straight fit up like the 29 or is there more to be done with it?
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Re: Drive Train Gearing Bible

Postby Blackdelux on Sun, 05 Nov 2017 6:33 +0000

hi all
can some one let me know if we can use 150 series prado diffs?
thanks in adavance
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Re: Drive Train Gearing Bible

Postby kevinreid89 on Sun, 18 Feb 2018 6:16 +0000

Can anyone confirm the Prado 120 series front and rear diffs are a straight swap with a 2012 SR Hilux diffs and nothing else to worry about?
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Re: Drive Train Gearing Bible

Postby VMN on Sun, 18 Feb 2018 6:33 +0000

kevinreid89 wrote:Can anyone confirm the Prado 120 series front and rear diffs are a straight swap with a 2012 SR Hilux diffs and nothing else to worry about?


This is what I did years ago.

The front diff housing will work but keep your axle tube.

The rear will work but I think some of the bearings are different which might surprise a diff shop if you break something and they have to rebuild it.... Of course I've never broken a single diff... it has been 3!....
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Re: Drive Train Gearing Bible

Postby kevinreid89 on Sun, 18 Feb 2018 6:47 +0000

I was trying to avoid swapping axle tubes will the prado axle tube not work? As in I was hoping it was a straight forward swap including the axle tube and without opening the diff?
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Re: Drive Train Gearing Bible

Postby VMN on Sun, 18 Feb 2018 7:06 +0000

The tube is a different part number. It probably also has ADD attached which the SR does not have. Its held on by 4 bolts so its not hard.
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Re: Drive Train Gearing Bible

Postby Blackdelux on Mon, 28 May 2018 2:02 +0000

Hi all
looking for advice .

im thinking of puuting 3,9s into my existing hilux that runs 3.7s Diese 4 spd auto
i run 265 70 17 wheels just under 32 inch

can anyone advise if this would be enough?
was thinking 4.11 might make me run to high in rev range im a tourer and do a bit of towing
dont want a roar or noisey car

has anyone gone 3.9s in 4speed auto??

i am i being too conservative? i do have lock up torque coverter.
i have checked first page of ratios and would suggest 4.11

looking for real world feedback

thanks in advance
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Re: Drive Train Gearing Bible

Postby VMN on Mon, 28 May 2018 3:05 +0000

I think I would stick to the 4.1's. Since I wrote the original post, I made up a table that does not lend itself to be published on the forum which I've always had on the VMN web site
See https://www.vehiclemods.net.au/page/hil ... 2005-2015/

Also there is now a nice complete package for 4.1 gears available which we order in on request (allow about 2 weeks).
https://www.vehiclemods.net.au/toyota-h ... regear-kit

We also supply the Harrop Elockers (You need the 3.73 and down) for the gear set above.
https://www.vehiclemods.net.au/spare-pa ... tion-aids/

With 3.9's there is no easy package and if you are not careful you'll end up buying gears from Toyota.

As far as real world experience, I've done a lot ot towing for a 1800kg caravan on 265/75 R16's and 4.1 gears. They are similar size to your proposed size.

Just drop it into third (as per the manual) and it will chug along all day. I could never get it to idle along in 4th gear even on flat ground around Broken Hill. I used to sit on about 92 km/hr (100km on the speedo). In 110 km speed zones, I'd sit on 100km/hr which is 110 km on the dial. It was also still fine at 110 km/hr if I had to get somewhere but hey a caravan implies a holiday! :)
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Re: Drive Train Gearing Bible

Postby Blackdelux on Mon, 28 May 2018 3:33 +0000

thanks Rod
great reply thanks for the time
im assuming those revs on your table are in 3rd gear auto as im sitting at 1900-2000 rpm in 4th at 100
and 2500 in 3rd.
i tow in 4th with it locked up thru converter switch, in 3rd feels like its revving too high already
but i am a lead foot. maybe i need to slow down.
i have killed an auto already, why im looking to re gear.
if im going to hold it in 3rd im leaning toward 3.9s
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Re: Drive Train Gearing Bible

Postby VMN on Mon, 28 May 2018 3:48 +0000

No, the table is in top gear at 100 km per hour based on nominal tyre circumference and allowing for all t/case and diff gearing. Towing was not a consideration.

Depending on the trailer weight, tow in 4th at your own peril. As you know, gearboxes are expensive to repair. Its a diesel motor. I think from memory it was 2700 rpm in 3rd at 92 km per hour which felt comfortable for the weight behind. Note that I joined this forum 5 years before you did and my Auto is still going strong and I hammer it except when towing.

Good luck finding 3.9's. If you are going to regear, don't be half arsed. Do it right or don't bother at all otherwise the expense is not warranted. The only guy I can remember who went with 3.9's had a manual and got it done at Toyota when he bought the truck. I think it broke half way across the Simpson. 4.1's are a better match for the auto.
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Re: Drive Train Gearing Bible

Postby Blackdelux on Tue, 29 May 2018 6:37 +0000

thanks again Rod
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Re: Drive Train Gearing Bible

Postby hiluxxury on Tue, 29 May 2018 7:54 +0000

I just found this youtube on another site - some real dyno numbers on HP and torque reduction with larger tyres

https://youtu.be/l1ULmPulZck
I might be wrong.

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Re: Drive Train Gearing Bible

Postby hornunga on Tue, 09 Nov 2021 3:22 +0000

Sorry if ive missed this info somewhere but, Has anybody swapped n80 diffs into their n70?

Looking at going for 3.9 or 4.1 gear change and before i go out and find a wrecked prado just chasing some more info.

Ive read through a few topics on here, from what i understand the n80 front will bolt into our n70.
The n80 rear is 8.8” but the n70 is only 8” so a diff center swap is out of the questuion. What about swapping over the entire axle along with it and running a larger diff center potentially with or without a factory locker.
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Re: Drive Train Gearing Bible

Postby VMN on Tue, 09 Nov 2021 3:39 +0000

You will be hard pressed to find a wrecked Prado with 4.1's
Nitro is out of stock of 4.1's globally until the new year.
The N80/N70 front housing is the same except the usual 3.9 and up and 3,7 and down equation which require different centres.

I'm not sure about swapping the rear N80 diff lots to consider there. The leaf springs are different, they run different gearboxes so the tailshaft lengths are probably different.

The content of this bible I wrote circa 2010 has mainly moved to https://www.vmn.com.au/ where some of the tables can be better formatted. Refer to our resource centre on that site.

Long and the short, best ratio for all tyre sizes 32"and up is the 4.1. At 35's the 4.5s are the best match.
The Nitro gear sets are "thick" cut so will fit the standard Hilux N70 centre. Most often though people will fit a Harrop elocker while they are apart. They also have been hard to get stock of. We have some in stock and have generally been able to fill orders even when Harrop are out of stock.

We have a number of Nitro 4.1's on backorder so feel free to join the queue. We expect to have stock before the Aussie distributor via airfreight instead of sea.
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Re: Drive Train Gearing Bible

Postby chada398 on Wed, 10 Nov 2021 6:08 +0000

Anyone know if hiace crown and pinion work? looking for 3.9s. 8" crown wheel in hiace but I think the splines may be different? thanks
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