Thread: Truetrac Diffs What I've Learned.

I have a new ATB in the shed. I think it has bearings. I know it has an ashcroft shim kit. PM me if interested.
Cheers, Adam.

Hello Kreecha!

Ashcroft also make an auto torque biasing centre diff. Not only does it rid your pocket of money, it also gets rid of OEM centre diff issues, which could be considered a saving in the long run. I've installed one in my Disco 1 and you don't notice its there.

Seems it is relatively easy to destroy the OEM centre if it is unlocked at the time of significant wheel spin.

The unlocked OEM centre diff apparently is not designed for fast rates of differentiation.

Unlocked, the OEM centre is ok on tarmac where four wheel traction is pretty much guaranteed and rates of differentiation are small when going round corners etc.

Different story in the rough stuff - the brass shims in the diff cannot cope with wheel spin for extended periods. I've taken four of the centres apart and found the brass shims embedded in sediment, which can't help with lubrication (some of the shims were worn away entirely!).

It is possible to get caught out when on firm soil with occasional soft patches. Its a pain to keep locking the OEM centre for every soft patch so you power through successfully time after time unlocked. But you then misjudge the extent of one patch, resist locking the centre, get lots of wheel spin then damage the centre OEM diff.

The Ashcroft unit gets rid of the shim wear/lube issue, gets rid of the weak two pin carrier arrangement, removes the need to constantly lock and unlock to avoid damage. It apparently can remain unlocked until you decide you want a 50:50 power split between front and rear drive shaft.

What happens past the drive shaft will depend on traction conditions and what you have in your rear and front diffs. I have lockers front and rear.

At a minimum I would go with an ATB in the centre - not to produce a 'macho' machine but rather to remove a significant potential weakness in the drive train, followed up with a rear locker or ATB.

Originally Posted by workingonit

Hello Kreecha!

Ashcroft also make an auto torque biasing centre diff. Not only does it rid your pocket of money, it also gets rid of OEM centre diff issues, which could be considered a saving in the long run. I've installed one in my Disco 1 and you don't notice its there.

Seems it is relatively easy to destroy the OEM centre if it is unlocked at the time of significant wheel spin.

The unlocked OEM centre diff apparently is not designed for fast rates of differentiation.

Unlocked, the OEM centre is ok on tarmac where four wheel traction is pretty much guaranteed and rates of differentiation are small when going round corners etc.

Different story in the rough stuff - the brass shims in the diff cannot cope with wheel spin for extended periods. I've taken four of the centres apart and found the brass shims embedded in sediment, which can't help with lubrication (some of the shims were worn away entirely!).

It is possible to get caught out when on firm soil with occasional soft patches. Its a pain to keep locking the OEM centre for every soft patch so you power through successfully time after time unlocked. But you then misjudge the extent of one patch, resist locking the centre, get lots of wheel spin then damage the centre OEM diff.

The Ashcroft unit gets rid of the shim wear/lube issue, gets rid of the weak two pin carrier arrangement, removes the need to constantly lock and unlock to avoid damage. It apparently can remain unlocked until you decide you want a 50:50 power split between front and rear drive shaft.

What happens past the drive shaft will depend on traction conditions and what you have in your rear and front diffs. I have lockers front and rear.

At a minimum I would go with an ATB in the centre - not to produce a 'macho' machine but rather to remove a significant potential weakness in the drive train, followed up with a rear locker or ATB.

Having said that though, I've not heard of an awful lot of centre diffs going pop, not enough to justify the cost of the centre LSD anyway

Yes, I thought the same until I started taking them apart to see how they are made and also looking around on other forums. And Ashcroft wouldn't make them if there was no demand I guess. Like you, I still have some lingering doubt about the frequency and cost benefit thing. But its a relatively inexpensive swap doing it yourself, that it gets rid of all the doubt. And it does mean you have a limited slip diff effect unlocked to boot.

You're fine if you lock them. But the big debate is when to do so. Some argue as soon as you see loose surface ie all the good weather gravel roads we travel on here in Oz for example. This concerns people that the vehicle centre diff is locked on what we call a good road. From a South African site:

"So, where do I lock the centre diff and where do I unlock it ?

If you are going off tar where there is a possibility of loosing traction, engage the centre diff lock. i.e. Up and down hills, mud, ice, snow, uneven surfaces.

Do not use any diff lock on tarred / concrete surfaces or any similar high traction surface, the difference in front to rear axle speeds will cause extreme torque build-up in the transmission to such an extent that transmission components will wear excessively and/or snap. This build-up is called "wind-up", Even a little hard surface driving in diff lock will cause the diff lock to not dis-engage due to transmission tension"

The hand book that comes with the Disco 1 says in regard to slippery surfaces (ice, snow, mud, grass) that the diff lock be engaged...always disengage diff lock when smooth, firm ground is reached.

Unfortunately a European condition perspective. So in which camp do our pea gravel roads sit - loose or firm?

I was once travelling a wide well graded 'firm' road in the Braidwood area, about 80kmh, in a Toyota part time 4x4 ie I was in rear 2 wheel drive. I took my foot off the accelerator, then feathered the brakes as I approached a cross road. I felt the tail move out, tried correcting, but found myself doing a 360 degree rotation - all I could do was sit there and watch the scenery go by. Maybe if I had rally driving experience it might have been a different story? Picture a Disco with an unlocked diff with wheels doing very different speeds maybe? Would it been a safer ride with diff lock engaged?

Interesting discussion based on hard off road use

Are Land Rovers inherently weak?

And other stuff

Transmission: GearBox, Transfer-Case and Clutch
Land Rover FAQ - Repair & Maintenance - Range Rover
http://www.aulro.com/afvb/discovery-...-broken-2.html
http://www.aulro.com/afvb/technical-...-damage-2.html
Defender Centre Diff broken ? - 4x4 Community Forum
Land Rover Diff Conversion and Differential locker for Landrover
LT230 Centre diff damage

Yes, I thought the same until I started taking them apart to see how they were made and also looking around on other forums. And Ashcroft wouldn't make them if there was no demand I guess. Like you, I still have some lingering doubt about the frequency of failure and cost benefit thing - but without reliable stats, but obvious mechanical deficiencies unlocked what to do? Its a relatively inexpensive swap doing it yourself, that it gets rid of all the doubt. And it does mean you have a limited slip diff effect unlocked to boot.

You're fine if you lock them. But the big debate is when to do so. Some argue as soon as you see loose surface ie all the good weather gravel roads we travel on here in Oz for example. This concerns people that the vehicle centre diff is locked on what we call a good road. From a South African site:

"So, where do I lock the centre diff and where do I unlock it ?

If you are going off tar where there is a possibility of loosing traction, engage the centre diff lock. i.e. Up and down hills, mud, ice, snow, uneven surfaces.

Do not use any diff lock on tarred / concrete surfaces or any similar high traction surface, the difference in front to rear axle speeds will cause extreme torque build-up in the transmission to such an extent that transmission components will wear excessively and/or snap. This build-up is called "wind-up", Even a little hard surface driving in diff lock will cause the diff lock to not dis-engage due to transmission tension"

The hand book that comes with the Disco 1 says in regard to slippery surfaces (ice, snow, mud, grass) that the diff lock be engaged...always disengage diff lock when smooth, firm ground is reached.

Unfortunately a European condition perspective. So in which camp do our pea gravel roads sit - loose or firm?

I was once travelling a wide well graded 'firm' road in the Braidwood area, about 80kmh, in a Toyota part time 4x4 ie I was in rear 2 wheel drive. I took my foot off the accelerator, then feathered the brakes as I approached a cross road. I felt the tail move out, tried correcting, but found myself doing a 360 degree rotation - all I could do was sit there and watch the scenery go by. Maybe if I had rally driving experience it might have been a different story? Picture a Disco with an unlocked diff with wheels doing very different speeds maybe? Would it been a safer ride with diff lock engaged?

Interesting discussion based on hard off road use

Are Land Rovers inherently weak?

And other stuff

Transmission: GearBox, Transfer-Case and Clutch
Land Rover FAQ - Repair & Maintenance - Range Rover
http://www.aulro.com/afvb/discovery-...-broken-2.html
LT230 Centre diff damage
Defender Centre Diff broken ? - 4x4 Community Forum
Land Rover Diff Conversion and Differential locker for Landrover
LT230 Centre diff damage

Seems it is relatively easy to destroy the OEM centre if it is unlocked at
the time of significant wheel spin

Err I don't really think that is true for most situations.

If one front spins then the other compensates through the axle diff and the front and rear drivelines are probably roughly at the same speed.

Now if you really hit it with a front spinning the driveshaft speeds may start to differ but with any mechanical sympathy the driver shouldn't reach that stage.
As described by the Seth African, it is more likely to damage a centre diff if you climb a steep hill unlocked and make air with the complete front axle and smash the centre cross shaft as you land.
IMHO this is driver abuse.
In all my 30 years of driving Land Rovers offroad I have never personally seen a centre diff go bang, but I have seen maybe 6-8 rear diffs go bang from excessive wheelspin and broken a rear axle myself with a detroit locker ( again from the red mist.) The LT95 centre diff in my 77 RRC had minced the thrust washers but it had done 300+Kk and looked to have been an offroad comp car at some stage.

So I doubt that it is really such a problem to need a Ashcroft Torque Biassing centre diff, but their Auto torque biassing feature would be nice.

But then why not get a second hand Borg Warner and put a new rear output shaft and possibly chain in it. The result would probably be better than an Ashcroft.

Regards Philip A

I reckon an ATB in the centre diff would eliminate a bucket load of backlash and be nice on fast but loose surfaces.

In fact I'll be doing just that fairly soon as I reckon there'll be no thrust washers left in my t/case after 320,000km anyway....

My experience in opening them up.
600,000km several thrust washers gone entirely.
300,000km all there but several as thin as cigarette paper.
200,000km most about half worn.

Interference rub marks on the two overlapping pins.

I agree Philip, I've not had any go or known other people directly that have - and maybe yours is a strong argument not to replace. As an owner you are faced with:- strong anecdotal evidence from users, mechanics and aftermarket manufacturers that they break due to thrust washer damage or pin damage; and direct take apart visual observation of construction, and condition at various mileages. It could be argued that after 200-300kms the diff needs taking apart for de-sludging and replacement of worn parts, so from my point of view replacing it with a new ATB is an extension of the service, albeit a bit of coin. And maybe breakage is not really an issue, but it is out the door for me regardless, with added limited slip equivalent as a bonus. Some argue you don't need rear lockers for similar reasons to not replacing the centre diff.

Trying to understand the analogy. Correct me if I'm wrong. Going forward, all 3 diffs open, drivers side front wheel lifts - rear drive shaft and axles stop rotating - front drive shaft rotates - front left axle stops - front right axle rotates receiving all power. The centre diff has to rotate quite rapidly to differentiate between stationary rear drive shaft and still rapidly rotating front drive shaft?

PS re-reading your example, seems premised on maintaining forward momentum while one wheel has lost traction in an all open diff situation - true, but for how long I'm wondering...down hill yep, level not for too long, up hill not likely?