Buying a Prado 120 Front Diff - what to look for

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Buying a Prado 120 Front Diff - what to look for

Postby rodw on Sat, 27 Feb 2010 7:30 +0000

Hi guys, I know the drive train gearing bible includes a lot of stuff and it is hard for some to interpret so I thought I would put up a quick post to show you guys what to look for if you start looking around the wreckers. Maybe the mods might like to sticky this thread too!

You basically have 2 options when regearing:
1. Buy new crown wheel and pinions from Toyota or Locktup.
2. By a matched pair of Prado Diffs from the wrecker.

the most cost effective option will depend on the ratio you want to run. Toyota quoted me $880 for the front Crown wheel and pinion (4.1 ratio) and I could have bought a pair of 4.5 ratio ones from Locktup for the same money.

One advantage of going the prado diffs from the wrecker route if you are fitting lockers is that the lockers can be fitted before your truck is pulled apart which measn that your car could only be off the road for one day. I paid $770 for the front diff and the read diff will be a similar price from the wrecker maybe $650 on a good day. They sem to want a bit more for the rear as it is a LSD.

The Hilux and the Prado 120 run a 8" front diff crown wheel and the earlier Prado 90 had a 7.5" Crown wheel. Apparently the rear diffs on the Prado 90 are the same but they might have a different flange to bolt the drive shaft on to but you can swap your flange over. I purchased some diffs from a friend who runs a wrecker and he had a Prado 120 rear diff and what he thought was the matching front diff. However it turned out that the front diff I got from him was a 7.5" one and we can only assume it came out of a Prado 90.

Anyway here is the diff you need to buy.
Prado 120 8" Front Dif - fits Hilux 150
Image

Sorry but I realised I took this pic with the diff upside down, but you can see here that the axle tube is a cast piece.

Dont Buy this one:
Prado 90 7,5" Front Diff - Does NOT fit Hilux 150
Image

This diff has a couple more components attached to it (eg mounts and inner CV drive shafts) but you can see that it has a welded in tube, NOT a cast part.

You can also see that the casting around where the axle tube bolts onto the main housing is also quite different.

Prado 120 Diff axle tube mounting bolts
Image

This pic also shows why they call this a clamshell diff because of the way they bolt together.
Prado 90 Diff Axle tube mounting bolts
Image

The other thing to look at is the bolt holes to accept the diff mounts as they are in different positions

Prado 120 Diff mounting holes
Image

Prado 90 Diff mounting holes
Image

Finally, it might be worth noting that you don't use the axle tube when fiting these parts as it has a different part number to the Hilux one. However, the front diff housing is the identical part number between the Prado 120 and the Hilux 150.

I would aslo suggest that if you do open the diffs to fit lockers that you specify that they replace bearings and seals while you are at it. This might prove problematic on the front diff as it ueses an european bearing which is only available in the country and was not available when I upgraded my diffs.

Suggested Diff Ratios by tyre size

This is just a place holder and when I get a chance, I will summarise all of the diff info in the bible so that it has an at a glance selection chart.

Anyway, happy diff shopping guys!
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Re: Buying a Prado 120 Front Diff - what to look for

Postby Skog07 on Sat, 27 Feb 2010 8:13 +0000

Good info there Rod.
Well done.
Topic stickied in the Drivetain Forum
Cheers
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Re: Buying a Prado 120 Front Diff - what to look for

Postby 4wd26 on Sun, 28 Feb 2010 5:10 +0000

rodw wrote:One advantage of going the prado diffs from the wrecker route if you are fitting lockers is that the lockers can be fitted before your truck is pulled apart which measn that your car could only be off the road for one day. I paid $770 for the front diff and the read diff will be a similar price from the wrecker maybe $650 on a good day. They sem to want a bit more for the rear as it is a LSD.

Anyway, happy diff shopping guys!


Another reason for the pricey rear diff- is the "diff club"
http://www.pradopoint.com/viewtopic.php?f=10&t=1206&st=0&sk=t&sd=a&hilit=diff+club

Not sure if you need to be a member of Pradopoint to enter, but there is a 8 page thread on busted rear diffs.
Just something to be aware of- especially if you add larger diameter tyres and lower the diff ratios.

Mind you seems rear lockers (ARB provide a new centre) may fix the problem
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Re: Buying a Prado 120 Front Diff - what to look for

Postby rodw on Sun, 28 Feb 2010 6:04 +0000

Hmm, interesting read Selwyn. Returned my wrong Prado 90 diff today and Dennis reckons the price of the front was up to $950 in southern states from the phone calls he made looking for one for me.

I was interested to read about the differences in low range gearing between the Prado and the Hilux whch might also be a contributing factor.
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Re: Buying a Prado 120 Front Diff - what to look for

Postby Sinan on Mon, 27 Feb 2012 7:44 +0000

Ok so to cut a long story short I am mechanically minded but when it comes to diffs my brain just packs up and walks out. Now is the front diff a complete replacement with the 120 series prado? I mean like pull axles out undo mounts, rip the Hilux diff out and just dump the prado one in there process? What happens with add on the sr5 model and what model prado.(diesel petrol auto manual?)

And next question is the rear.
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Re: Buying a Prado 120 Front Diff - what to look for

Postby Skog07 on Mon, 27 Feb 2012 8:00 +0000

Some good points there Simon.
Rod has put together a very comprehensive guide on how to select a diff for the Hilux.
The 120 will fit, but there will always be some niggling fitment problems that may need to be recified.
Im no guru but their is one flaw with fitting a Prado diff to an SR5 model hilux. You will lose your ADD ability. ADD is auto disconnect differential. The Prado is a full time 4wd and does not have any ADD options available. Gearing may be a better option.
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Re: Buying a Prado 120 Front Diff - what to look for

Postby helmut79 on Mon, 27 Feb 2012 8:11 +0000

Sinan wrote:Ok so to cut a long story short I am mechanically minded but when it comes to diffs my brain just packs up and walks out. Now is the front diff a complete replacement with the 120 series prado? I mean like pull axles out undo mounts, rip the Hilux diff out and just dump the prado one in there process? What happens with add on the sr5 model and what model prado.(diesel petrol auto manual?)

And next question is the rear.


Mate you a diesel auto 3.73 diff with 33's, the 4.1's the prado offers still is not high enough to provide stock gearing 3.73/29 *33 = 4.24 no such animal for our rigs.

Have you thought about the 4.56's thick cut gears? No need for new carrier / diff just buy the crown wheel and pinions and swap them out.

4.56 will give a slow crawl in the auto and down hill down side the car will rev higher at HWY speed (estimate is about 200rpm)

Just some food for thought
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Re: Buying a Prado 120 Front Diff - what to look for

Postby McSumWay on Tue, 28 Feb 2012 3:23 +0000

Sinan wrote:Ok so to cut a long story short I am mechanically minded but when it comes to diffs my brain just packs up and walks out. Now is the front diff a complete replacement with the 120 series prado? I mean like pull axles out undo mounts, rip the Hilux diff out and just dump the prado one in there process? What happens with add on the sr5 model and what model prado.(diesel petrol auto manual?)

And next question is the rear.


All you actually need are the internals ie: the crown wheel and pinion and the centre. Theses can be fitted into your existing diff with ADD and will run as normal.

Then change the internals at the rear but all you need there is the crown wheel and pinion as the centre is the same between them both.
I have nothing good to say down here so I wont say anything at all
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Re: Buying a Prado 120 Front Diff - what to look for

Postby VMN on Tue, 28 Feb 2012 5:39 +0000

I think Helmut's Math is is a bit suspect as the ratios are determined by the circumference not just diameter. This page on my website shows all of the diffs
http://www.vehiclemods.net.au/hilux-150 ... drivedrain

Whilst not perfect, the 4.1 remains the closest match to 33's from this table.

I might stand corrected, but I thought that the ADD was all contained on the axle tube and the diff housing was the same part number on the Hilux and Prado. Therefore swapping the diff over and keeping the Hilux axle tube which is held on by 4 bolts should retain the ADD. Anyway, that was the outcome from the initial research Max and I did. My truck is an SR so I don't have direct experience but i did retain the axle tube.

Just a reminder that VMN can supply the very hard to source front diff rebuild kit. There have been a few outages of the rear diffs from Nitro but Yukon have been in stock so just make sure you have all bases covered if you do this.NAS a guide, you are up for about $1200 in parts for all of the parts to do the rear diff and the front rebuild kit leaving you just with the need to source the front crown wheel and pinion and carrier (or locker).
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Re: Buying a Prado 120 Front Diff - what to look for

Postby Hilux Max on Tue, 28 Feb 2012 4:42 +0000

Depends on the needs of the driver Rod.....4.1's on the auto and 33's still wont give it the same low range gearing as standard , thou close yes.

But extra diameter/circumference also adds more load...the 1st gear of the auto being tall as it is, so if your going to tow, wheel your rig offroad or go a larger tyre later on then 4.5 is the better choice in my opinion...small sacrifice of 200rpm extra at 100kph.
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Re: Buying a Prado 120 Front Diff - what to look for

Postby VMN on Tue, 28 Feb 2012 5:40 +0000

mmaaxx wrote:Depends on the needs of the driver Rod.....4.1's on the auto and 33's still wont give it the same low range gearing as standard , thou close yes.

But extra diameter/circumference also adds more load...the 1st gear of the auto being tall as it is, so if your going to tow, wheel your rig offroad or go a larger tyre later on then 4.5 is the better choice in my opinion...small sacrifice of 200rpm extra at 100kph.


I don't disagree on this. The table is pure theory but few will have the opportunity to trial the different choices due to costs involved. Basically the difference is the same if you went from factory tyres to 31's and then went back to factories again. You won't notice it much at all.

Given I tow a 1800 kg van, I think the factory ratios are fine unless your trailer is at or beyond the legal limit provided you adhere to the correct gears as advised in the user manual to keep exhaust temps in check.

If your primary driving is off road then go 4.5's, if you don't wheel that much and most of your driving is on the road, go with 4.1's and you will maximize the fuel consumption improvement which will eventually pay for your gearing.

If you are towing big loads, maybe the choice of 33's is questionable.
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Re: Buying a Prado 120 Front Diff - what to look for

Postby Hilux Max on Tue, 28 Feb 2012 5:54 +0000

spot on ol fella :mrgreen:
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Re: Buying a Prado 120 Front Diff - what to look for

Postby helmut79 on Tue, 28 Feb 2012 6:03 +0000

VMN wrote:If your primary driving is off road then go 4.5's, if you don't wheel that much and most of your driving is on the road, go with 4.1's and you will maximize the fuel consumption improvement which will eventually pay for your gearing.


I still think I will get a fuel saving from fitting the 4.5's, well it will return to the same as when I was running 31's
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Re: Buying a Prado 120 Front Diff - what to look for

Postby VMN on Tue, 28 Feb 2012 6:32 +0000

helmut79 wrote:I still think I will get a fuel saving from fitting the 4.5's, well it will return to the same as when I was running 31's


Mick, there's no doubt you'll notice a difference as you will be 500 rpm different to where you are now at 100 km/hr. Your fuel consumption will no doubt improve but maybe not as much as if the factory gearing was restored. By saying that, I am assuming that the factory spec would put the truck at optimum rev range for fuel consumption as that is how the power/torque curve maps to fuel consumption. But if you look at the factory gearing, there is some leeway as there is roughly 100 rpm difference across the model range as they come from the showroom floor.

However, I think you have it wrong about the 31's. The rpm you will be doing will be closer to what it would be if you put factory 29's back on and regeared to 4.1's
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Re: Buying a Prado 120 Front Diff - what to look for

Postby vortexheli on Tue, 30 Oct 2012 6:27 +0000

Anybody know the diff code for a 120 prado front diff in 4.1?

Tried google without much luck

the wrecker I am dealing with wants to know it before they send it to me,

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Re: Buying a Prado 120 Front Diff - what to look for

Postby Hilux Max on Tue, 30 Oct 2012 6:53 +0000

Your after the actual code itself on the diff housing yeah, not the part number of the 4.1 factory front gears?
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Re: Buying a Prado 120 Front Diff - what to look for

Postby 06lux on Wed, 07 Nov 2012 6:13 +0000

okay i have done alot of reading and asking questions about diffs.
what i want to clear up is regarding the front diff. can i run 4.1 gears in the front without having to change the complete diff. i.e keep the hilux diff and change internals? reason im asking is at the moment with the mr diff drop brackets my cv's are completely level with 2.5" of lift and not 100% sure that the brackets would bolt up the the prado diff. if this is the case ill loose my flat cv angle. i know a lil bit of an angle doesnt hurt but id rather have them as flat as possible. also it would save me alot of time searching round the wreckers and id rather buy new.

and rears is all that needs to be done is get my locker and 4.1 crown and pinion gears and thats it? when ordering the locker do i get one to suit the prado 4.1 diff?

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Re: Buying a Prado 120 Front Diff - what to look for

Postby Hilux Max on Wed, 07 Nov 2012 6:56 +0000

get a front prado 120 locker for the 4.1 diff gears or a prado 120 factory carrier.

rear, just get the gears and locker and install.
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Re: Buying a Prado 120 Front Diff - what to look for

Postby 06lux on Wed, 07 Nov 2012 7:01 +0000

at this stage max im just going rear locker. dont have enough cash aside for both yet. so the prado carrier slots into the front hilux diff?
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Re: Buying a Prado 120 Front Diff - what to look for

Postby calis101 on Tue, 11 Jun 2013 10:34 +0000

So does the 120 housing bolt in? I have one at the diff shop atm getting a locker fitted and am now having second thoughts... should I just use the original housing? As I have an sr ADD is not an issue?
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