T-case splitting uneven torque?

[Crispin]

I've been wondering.... (as you do on a Friday afternoon)

The landcruiser is a permanent 4x4 with, AFAIK, a 50/50 split front and rear.
How do you obtain anything other than a 50/50 split? Normal AWD cars like Audi Quatro, Scooby etc are normally a 60/40 split.

What confuses me is that if you have an input shaft with a gear on it which drives another shaft (output) which is then sent to the front and rear diff, how can you provide "more" torque to one end?

I have oversimplified the t-case workings (centre diff etc) but where does the "magic" lie? In the t-case of each diff?

Cheers,
Crispin

 

[Chris]

I too have always thought that the LC (OK the 90 and 120) had some form of torque sensing diff that could give 100% to rear up to 50 + 50 split when needed. I have always though that odd in terms of being 4x4. Now the 80 I think used to have full time 4x4 on the back door didn't it? I took this to be different from permanent 4x4. The subtlety being that Perm meant that you didn't have to select it and full time meant always being driven. Prof Bob has blown this apart with his journey into the t box on a 90 which clearly shows that the front and rear shafts receive the same drive. Yes, the centre diff splits the drive, but not the torque. So I am sort of still confused. I know the result at the wheels, just not all of the science. When I bust my diff, I removed the rear prop. I then had zero forward drive. All drive went to the rear flange. Only when i put it in cdl could I drive it. What happens on an 80 if you do that - same thing?

C

 

[Gary Stockton]

Not sure whether this is T-Case or centre diff technology, but an animation I saw recently of the 150 climbing and going over a 'mogul' showed power variation from front:rear axles of 60:40%, then 50:50% on the level, then 40:60% going down-hill. Interesting stuff. Can you imagine the noise trying to get up Rubies Hill Traction Control, diff switching, brakes, engine - chaos ...

 

[PtP]

........How do you obtain anything other than a 50/50 split?..........

You require a Viscous Coupling instead of the current centre diff. I doubt you'll get one though. They become a source of problems as they seize up and effectively create a locked centre diff. If your front tyres for example are worn slightly more than the rears, then the Viscous Coupling is constantly working away and eventually seizes. With an open centre diff as on the LC you don’t have this worry, you can just lock it to give you equal drive to the front and rear wheels.

Have a read here: http://www.mrtrally.com.au/performance/ ... upling.htm

 

[Malcolm Bagley]

........How do you obtain anything other than a 50/50 split?..........

You require a Viscous Coupling instead of the current centre diff. I doubt you'll get one though. They become a source of problems as they seize up and effectively create a locked centre diff. If your front tyres for example are worn slightly more than the rears, then the Viscous Coupling is constantly working away and eventually seizes. With an open centre diff as on the LC you don’t have this worry, you can just lock it to give you equal drive to the front and rear wheels.

I think the first Freelander used different diff ratios to split the drive torque, coupled with a VC, worked OK for me when I had one although I did hear about couplings failing, given the task they do I am not too surprised.

The lathe and torque wrench test in the link was interesting, the speed difference they use is 100 rpm and that must be below the lock up, always wondered what the speed difference would need to be for lock up.