Factory Locked Rear Differential- problems&solutions

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FirstToy

FirstToy

Joined
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This topic has come up in both Rubicon threads. I think it is important and deserves it's own thread.
The purpose is to discover technical information, identify problems & solutions as well as discussion on this topic.

The issue has come up that some people are experiencing blown rear diffs on the factory locked units. The Tacoma & Prado share this rear locked rear diff.

I am hoping this will help identify the issue and, in the end, benefit FJC owners armed w/ accurate information.

To get up to speed, here are the threads it was discussed
https://forum.ih8mud.com/showthread.php?p=1309971
https://forum.ih8mud.com/showthread.php?p=1291150&page=3

From TTORA (referenced from a thread at toyota120.com)
http://www.tacomaterritory.com/forum/showthread.php?t=35345
http://www.tacomaterritory.com/wiki/index.php/2005_Tacoma_Rear_Diff_Failures

Some quotes from Prado 120 owners taken from the Prado forum:

I have just come back from doing what I would consider easy offroading
on the Power lines track east of Perth. While attempting an up hill
climb with 1 wheel in the air front and rear I heard a very loud bang.
After getting to the top I noticed that when the rear wheels rotated
about 1 turn there would be a loud bang coming from the rear diff. I
was only able to drive the vehicle at a max speed of 40km/h. I will be
presenting the vehicle to Toyota tomorrow and I suspect my rear diff
has failed.

120 GXL V6 4L Auto
Toyota Alloy Bullbar
265/70/R17 Cooper ATR
King springs
All rest stock.

Regards
Doug Kernutt
Click to expand...


If you want to make the rear diff stronger, and stop the crownwheel flexing
away from the pinion, leaving the teeth unsupported, you need to fit an ARB
locker, which has a much stronger hemisphere, and no hole in the side of the
carrier to get the side gears in, and the diff needs to be set up with a
solid
pinion spacer, rather than the crushable type it comes with.

These mods wont prevent abuse breaking it, but they make the diff as strong
as
it can be.

And if you get the new crownwheel and pinion from toyota under warranty,
rather
than a whole new diff, which can do the same thing, it will allow you to
have the
mods done to strengthen it.

Regards Darren McRae
ATS 4X4 90 Fyans St Geelong Sth 3220
Click to expand...

Hi Doug God dam it i here to much of this issue i think we all should be
troubled by these failures i now now of 7 in the last 2 months regards Peter
Click to expand...

Doug

It has been the crown wheel in all instances that I have heard of
(including myself).


________________________________
Michael Fenech
Click to expand...

I know of 7 120 series. 3 of those in the same club.
Click to expand...

------------------------------
and from Greece, (posted on toyota120.com)
Going up a moderate short (about 30m) uphill my rear diff broke.
A tooth from th crownwheel was broken.
After doing some research on the net i found some similar cases in Australia and Europe as well.
The problem is that nobody had an explanation of why it happen on a car that is supposed to be famous for its strength especially the rear axle.

Did you have any similar incidents?
__________________
Landcruiser 120 D-4D 6sp manual LWB
ARB Sahara
Warn 9.5XP
Koni Heavy Track Raid suspension
STT Cooper 265/70-17

www.nomad.gr
Click to expand...

No nothing.
The wheel spinned a little then it gained traction and bang!!!
My rear diff wasn't even locked.

This guy from Spain had the same incident and below is a photo at the moment it happened.
http://fotos.miarroba.com/fotos/d/c/dcc3f4b4.jpg
Click to expand...
 
I to thank you for starting this thread. This may be jumping ahead a little bit but here it goes.
Since you have to have the rear locker from the factory to add the a-trac switch mod, would replacing factory locker with the arb locker screw up a-trac mod?
If not, then it looks like we have our mod for running a-trac and locker at the same time.
Just a thought.
 
Looks like a legitimate problem after all. Since the Prado, FJ Cruiser and 4-Runner all use the same diff etc, is there any way to force a Toyota Factory Recall to have them install new beefier components?
 
Interestingly, blown diffs are "common" in the minitruck crowd too...IIRC, the carrier for a Tacoma uses a bridge between the carrier bearing caps, specifically to prevent flexing in this area.......is this the same type of "fix" that would cure the issue with these diffs?
 
Tojo, if you installed a ARB locker(s) it would have no effect on ATRAC. Meaning, it would not disable or inhibit the normal operation of it. Once locked, ATRAC would be effectively turned off. Since it will not detect differential tire spin.

TexasBadlands said:
Since the Prado, FJ Cruiser and 4-Runner all use the same diff
Click to expand...

That is incorrect.
The 4Runner and GX470 do not have factory locked diffs. It is an option in the Taco & FJC. I don't know if it's standard in the Prado.

There is a difference between the open and locked rear diff.


woody said:
Interestingly, blown diffs are "common" in the minitruck crowd too...IIRC, the carrier for a Tacoma uses a bridge between the carrier bearing caps, specifically to prevent flexing in this area.......is this the same type of "fix" that would cure the issue with these diffs?
Click to expand...

I don't know but it sounds interesting. From what DMC said, sounds like the crown gear flex is the problem... is that the same?

more details or articles on this for minitrucks?
 
In the 2000 and newer 100's, A-Trac and the arb will work at the same time. I would assume that if one replaced the factory locker with an arb, it would provide the best of both worlds.
 
Dirk Diggler said:
In the 2000 and newer 100's, A-Trac and the arb will work at the same time. I would assume that if one replaced the factory locker with an arb, it would provide the best of both worlds.
Click to expand...

Yeah that would be great, but that would be at the owners expense, and not making Toyota liable for a problem which should not exist.

FirstToy, from what I have read the Prado spawned both the FJC and 4-Runner set ups, but that is of course just what I read.

I sent Toyota an email asking what they were going to do about it. I will update here if I hear back from them.
 
TexasBadlands said:
Yeah that would be great, but that would be at the owners expense, and not making Toyota liable for a problem which should not exist.

FirstToy, from what I have read the Prado spawned both the FJC and 4-Runner set ups, but that is of course just what I read.

I sent Toyota an email asking what they were going to do about it. I will update here if I hear back from them.
Click to expand...

To answer this question once and for all, the 4runner and the Fjcruiser, as well as the Lexus GX470 are all based on the Prado. Now there are several different verison/models of the prado and even variations from country to country. One thing that is quite different with Toyota of American Car companies is that they will have Models based on other models, and often have some very unique parts on each one (sometimes ones you would expect to be the same). The Prado is offered in both gas and Diesel models and some models are lighter duty than others, based on what the design is expected for (work/serice models, passenger use, off-roading, etc...).

I hope that helps with the question what american toyota models are based on and like the Land Cruiser Prado.

Cheers,

Michael
 
The history of the FJC is in the FAQ.
The 4R, Taco, GX, Prado & FJC open differential are the same. And I have heard of no problems w/ these. (Taco is different in that it has a leaf spring instead of linked rear suspension, of course).

From DMC's post
If you want to make the rear diff stronger, and stop the crownwheel flexing
away from the pinion, leaving the teeth unsupported, you need to fit an ARB
locker, which has a much stronger hemisphere, and no hole in the side of the
carrier to get the side gears in
Click to expand...

Maybe this is the ring gear flexing away from the pinion?
From Jerod's link, I guess it's possible Toyota didn't set enough preload?

Unfortunately, I'm out of my element but I'll keep raising the questions! lol

I am intersted in woody's minitruck "bridge" fix...
 
Just noticed the thanks at the bottom of woody's link.
Sean comes highly recommended by the Norcal Crew. Bulldog is going to get his 4th gen regeared/arb locked there later this year. I think he may have some definitive answers as well.

I would also like to thank Sean (aka "GearMan") at River City Differentials. He has been very helpful and doesn't seem to mind answering my many questions. He and his shop are highly recommended by members of the Toy4x4 mailing list Pirate4x4.com BBS, and others. Let him know his info is being put to good use!
River City Differentials
Rancho Cordova, CA
(916) 852-7109
 
FirstToy said:
I don't know if it's standard in the Prado.
Click to expand...

NO, are not standard on 90 or 120 models, so also are not available for all markets ( means not all countrys ) as same as LSD.
 
another one blown today- From Prado 120scool

Well, today was the day. While negotiating a reletively easy ascent
on Mt Mee near Brisbane today the rear diff went bang!! Thankfully I
was with a local 4WD club and was able to be snatched to the top.
After removing the rear drive shaft I limped back to the bottom to be
unceremoniously returned home on the back of a tilt tray. Well it's
off to Toyota tomorrow for the aftermath. We'll see what happens.

Geoff...

My vehicle is a GXL model which does not have a factory locked
rear diff. It has an LSD which is arguable not much help. I only
have the factory centre diff lock.

Geoff.
Front wheel drive Prado.
 
Last edited:
FirstToy said:
another one blown today- From Prado 120scool

Well, today was the day. While negotiating a reletively easy ascent
on Mt Mee near Brisbane today the rear diff went bang!! Thankfully I
was with a local 4WD club and was able to be snatched to the top.
After removing the rear drive shaft I limped back to the bottom to be
unceremoniously returned home on the back of a tilt tray. Well it's
off to Toyota tomorrow for the aftermath. We'll see what happens.

Geoff...

My vehicle is a GXL model which does not have a factory locked
rear diff. It has an LSD which is arguable not much help. I only
have the factory centre diff lock.

Geoff.
Front wheel drive Prado.
Click to expand...

I think we have reached the point of ridiculous. :eek: I'm afraid to take mine off-road now.

Michael
 
Michael,
I don't hear of many problems- when they are condensed into one thread, it maybe makes it sound worse than it is. It wouldn't stop me from enjoying the truck or anything.
I haven't noticed any other rear diff problems from FJC's so the odds are way on your side as far as possibly having the same problem. I would really like to know what is going on tho, for the benefit of the FJC owners.

I am of the mind that knowing is better than being in ignorance- altho ignorance is bliss! ;)

Another from 120scool

Dear All,

Here in Israel we have a vivid 4x4 club called "jeeptrip"
(www.jeeptrip.co.il <http://www.jeeptrip.co.il/> ) sorry it is in
Hebrew...we are several thousands member strong and quite few members
own the Prado 120 (introduced to Israel in 2004). With time many
complained about rear-diff failure on minor efforts. If it happens to
you - Toyota Israel repairs the first one free (if the car has less than
100,000k), but they give trouble to second occurrence claiming drivers
fault due to harsh off-roading...(serial killer). Those who were firm
enough got the second diff free as well... Toyota Japan is aware of the
problem in Israel, but we seem to be a much smaller market than the auzi
one...so take the lead and ask for recall...we will support you if
needed... especially if you ask Toyota to replace the rear diff with an
ARB locking one for free...(~...



Raphi Mandelbaum, Rehovot Israel...
 
Tapage, I think the Prados use the same RD23 ARB rear. Front air locker is being introduced by ARB asap, 2 versions for 2 diff. gearing.
 
FirstToy said:
Michael,
I don't hear of many problems- when they are condensed into one thread, it maybe makes it sound worse than it is. It wouldn't stop me from enjoying the truck or anything.
Click to expand...

I'll agree with this! I have been wheeling my FJC a number of times in some pretty challenging situations, and I have had no issue so far. I'll also remind everyone that the Trail Team has over 25K miles on their rigs and they haven't had an issue that I know of.

That being said, I don't know squat about pinions or rear gear flexing. So please keep it coming so if mine does crap out, I know why and what to do! Thanks!
 
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