What is "double diff"

[Mort]

Hi guys

I was chatting to someone who mentioned that their Jeep had "double diff". I have tried to do some research but have not come up with anything conclusive - would anyone be able to explain to me what this could be?

Many thanks!
Mort

[Dirk]

Maybe they meant double diff locks, like the Jeep JK Rubicons.

[jelo]

Your friend doesn't know a diff from a lump of cheese.

On proper 4x4 systems (not All Wheel Drive), you have two options:

- a transfer case without center diff, in other words, selectable 4WD: 2High (normal rear wheel drive) , 4High (equal locked drive to both front and rear, high range), 4 Low (equal locked drive to both front and rear, low range). Example: old Nissan Hardbodies, old Hiluxes, old Series Land Rovers, old Nissan Safaris, etc.

- a transfer case with a center diff, in other words, full time 4x4. You only have an option of 4H and 4L. The diff INSIDE the transfer case USUALLY (but not on all vehicles) is locked when in 4L. Some vehicle have this as an OPTION (Defender, Discovery 1, early Discovery 2, Range Rover Classic, etc), some have no center diff lock option, so drive is not 50/50 to both front and rear.

Ask him what he means by "double diff".

[Mort]

Maybe they meant double diff locks, like the Jeep JK Rubicons.

Thanks for the quick response Dirk Im (very) new to the 4x4 arena so please forgive my ignorance... Im still reading up but it takes a while to get it all sorted and understood as its a new topic

Would that be one locker on the front axle and one on the rear, or how does that work?

[Mort]

Your friend doesn't know a diff from a lump of cheese.

Thanks Jelo I will be asking him what he means as soon as I can

I have a few questions on your explanation just to make sure I understand each one, if you dont mind?

- a transfer case without center diff, in other words, selectable 4WD: 2High (normal rear wheel drive)

This is like a normal car, where drive is on 2 wheels and they can turn at different speeds, or are the 2 drive wheels locked to the same turning speed?

4High (equal locked drive to both front and rear, high range)

Is this where all four wheels are locked to all turn at the same speed, or are the front 2 locked together and the back 2 locked together?

4 Low (equal locked drive to both front and rear, low range). Example: old Nissan Hardbodies, old Hiluxes, old Series Land Rovers, old Nissan Safaris, etc.

Same question as above, all 4 together or front together and back together?

Many thanks!

[Mort]

@Jelo - or is the diff locking independant of the drive mode?

[Apocalypse]

He was probably referring to the fact he had double live diffs - as opposed to independent suspension.

For serious off road work this is the best suspension arrangement on currently available vehicles - defender, wrangler, pathfinder and 76 series cruisers are all that currently carry this arrangement, but most older jeeps , cruisers, patrols. Disco 1 and2 and old hiluxes also feature this...

[Mort]

He was probably referring to the fact he had double live diffs - as opposed to independent suspension.

For serious off road work this is the best suspension arrangement on currently available vehicles - defender, wrangler, pathfinder and 76 series cruisers are all that currently carry this arrangement, but most older jeeps , cruisers, patrols. Disco 1 and2 and old hiluxes also feature this...

Thanks for the info Apocalypse, Ill keep it in mind when I ask for more info...

Could you tell me more about this, or point me in the direction of where I can read up a bit more on it - Google is not being helpful, it keeps giving me Garth Brooks CD's

[Apocalypse]

Mort - what vehicle do you drive?

[Mort]

Mort - what vehicle do you drive?

At the moment a Renault Megane Coupe

I have been trying to get my grubby paws on a 4x4 for some time now, but you know how it goes - just as you think you can afford it life throws you a curveball

Today a friend mentioned that he was offered by his uncle to buy the uncles jeep, and he wanted to know if I was interested since he couldnt afford it. Im waiting for them to send me all the details, but at the moment it sounds almost too good to be true (you know what they say about those deals...). I shall reserve judgement until I have all the details though.

Im just doing some research so long into the details I do have...

[Apocalypse]

Okay, was just to make explanations easy!

A general use modern bakkie, 4x2 or 4x4 has a live rear and independent front.

Most top end SUVs have independent front and rear.

Proper 4x4s have a live front and rear. The exception is the hummer H1 which has long arm independent suspension with portal axles and inboard discs front and rear.

Basically if you look under any bakkie at the back you'll see a live axle. It has the off road advantage that it will rotate about the propshaft as much as the suspension will allow, on modded vehicles this is often 45degrees or so.

This means the wheels stay in contact with the ground AND upright relative to each other o. Obstacles, plus your clearance remains the same.

Independent suspensions are limited in travel by the cv joint Angle. Droop and bump is limited and the ground clearance disappears as it moves.

Basically lifts a wheel more easily and relies more on diff locks.

It's also much easier to lift live axles and fit bigger tyres.

Does that help?

[Mort]

Yes, thank you for all the detail When dealing with me you are safe in assuming complete n00b :P

Is there a reason the top end SUV's dont use the better live suspension?

[Apocalypse]

Yes, thank you for all the detail When dealing with me you are safe in assuming complete n00b :P
Is there a reason the top end SUV's dont use the better live suspension?

Yes. It's far superior for high speed activities, general road use and comfort.

Bump through, wheel control, steering the lot - all better on live suspension...

[Mort]

Ah ok, thanks for the info Ill update the thread with what "double diff" means when I find out :P

[Mort]

Oh right, one more thing Apocalypse - would double live diffs mean live suspension back and front then?

[Apocalypse]

Oh right, one more thing Apocalypse - would double live diffs mean live suspension back and front then?

Correct!!!

[BarOne]

If you were talking trucks, a double diff is a 6x4.

[Jean Kotze]

Mort,

People tend to get generally confused with different terminology when it comes to suspension systems. Just for clarification:

Axles

Firstly, all vehicles have axles. That is basically the line between two wheels on the same axis.


Dead and Live axles

The axles can then be either dead or live. If it has drive to the axle from the gearbox via a driveshaft, and hence it would have a differential (diff), then it is a live axle.

If it does not have drive, and therefore no diff, then it is a dead axle.

For example, a 4x2 rear wheel drive vehicle will have a live axle in the back and dead axle in front. Similarly, a front wheel drive 4x2 vehicle would have a live axle in front and a dead axle in the back.

All 4x4 or AWD vehicles will therefore have live axles front and back (i.e. they will have diffs on the front and back axles).

Dependent and Independent Axles

An axle can then also be either dependent or independent. Dependent means that the two wheels on the same axle are linked with a solid axle, and the two wheels would behave dependently of eachother.

On an independent axle, the wheels are seperately suspended with their own freedom of movement and does not impact on the other wheel on the same axle.

Both these axles can then also be either live or dead. For example, on a rear wheel drive 4x2 vehicle you may have a solid live axle in the back and a dead independent axle in the front (IFS).

In 4x4 vehicles, like the Jeep Wrangler, you will have two solid live axles in front and back.

In 4x4 bakkies (generally), like the Toyota, you will have a solid live axle in the back and an independent live axle in front.

In 4x4 vehicles such as the Pajero, you have independent live axles front and back.

Common erros:

Some people may incorrectly make the following statement:

Live axle - meaning solid live axle with diff
Diff - solid live axle

A live axle only means that it has drive to it. A diff is a differential and is part of the axle. Live independent axles also have diffs.

Hope this helps.

[Apocalypse]

Dead axle?

never heard it called that actually.

never heard it called solid live axle either. live axle = solid axle

and there is no such thing as a live independant axle either.

I suppose you might almost term a De Dion axle an indepenadent live axle as it drive shafts coupled to a live axle, but it's a bit silly to call it that...

where did you pick up these interesting terms Jean? was it google again?

[Apocalypse]

interesting, google does show use for the term 'dead axle.'

okay.

but it seems refers to a beam axle which does not transmit drive, I suppose it could refer to any axle which does not transmit drive, but as a independent suspension uses stub axles it would be a bit confusing to use in that context. usually you'd call that a beam axle. you do still get those on trucks, in fact, the current JK Wrangler has one if you order the 2WD version available in the states.

but in theory it refers to driven axles as opposed to type of suspension which is not really what the question is I think...

the terms front wheel drive, rear wheel drive and four wheel drive are far more modern and descriptive I'd think. maybe the term is used more for multiple axle trucks? not something I deal with much and when I have I've not heard the term, and it's kind of not relevant anyway I think...

but a live axle refers to an good old beam axle with a diff in the middle as found under most bakkies at the back, and Wranglers and older jeeps at both ends. you can't use it to refer to a driven axle if it's independent suspension...

probably not the best thread to confuse a newbie on hey Jean? there is a lot that is very cinfusing and contradictory in your poat!