1991 Classic Diff Lock or lack of

Hi Guys,

I noticed that my 1991 Classic doesn't have the Diff lock function. After some search and I realised it uses viscous coupling or something like that...I've only driven 4x4 on part time systems such as the SIII Landy. First timer to the permanent 4 wheel drive thingy..

Could anyone shed some light how this works?
How is it different to say the part time system on SIII Landy?
Should I adjust driving styles on-road or off-road with this system?

Thanks.

Your 91 will have diff lock, on the lever in front of your gearchange you will have a smaller lever that when moved forward will put you in low range it will also move sideways(to the left) this then puts you in difflock whether you are in high or low range (it can be put in difflock whilst moving). Permanent 4 wheel drive is perfectly ok for all but the most loose or muddy surfaces then it could be put in difflock for the added traction and the slow descents, but remember to take it out of difflock when the obstacle is cleared otherwise the diffs will "wind up".

stig said:

Your 91 will have diff lock, on the lever in front of your gearchange you will have a smaller lever that when moved forward will put you in low range it will also move sideways(to the left) ...

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That's the LT230 of earlier RRCs and Discos.

91 Classic has Borg Warner transfer box, which has viscous coupling.

To the original question: You do not have to change your driving style. When there is a speed difference between the prop shafts the viscous coupling starts to grip automatically preventing the slip.

Ha okay.....

So viscous coupling = automatic diff lock......or similar.....

So does it mean that when a slip occurs, sending the wheel with least or no traction spinning (say the left front), hydraulic oil in transfer case 'harden up' activating the viscous coupling hence locking up the center diff. Thus linking the front and rear propshaft to spin/travel at the same speed. This then result in torque being sent to the rear 2 wheels which in result moved the vehicle forward.

What happens when one of the front wheel spins, centered diff locked, then one of the rear wheel spins as well as one of the front.......not going anywhere I suppose....

So, in effect, vicous coupling works the same way as the lever diff lock on earlier models. Hence it is indeed a 2 wheel drive (meaning only either 1 wheel at the front or 1 wheel at the rear will be allowed to slip if the vehicle is to be able to move forward), unlike the series landy which in effect is a 1 wheel drive (1 wheel start spinning = no motion).

Please correct me if I am wrong.

That's correct. It works like a dream in my RRC. Although I would like to have ARB diff lock at rear. Then I would have a 3WD - I would have needed at least one wheel gripping a couple of times.

hmmmm......ARB diff lock...........thats another dream......

Not gonna get one fitted as I wont be doing any extreme offroading in this classic.

While we are on the topic of lockers, can I assume that lockers at the rear is okay, eg. air-locker like ARB or even Detroil style mechanical locker. But the front can only be fitted with selectable lockers like ARB's sirlocker while mechanical lockers such as Detroit are bad news???

A question of thoughts:
Since Borg Warner is viscous coupling, technically the front and rear diffs are 'seperated', meaning they could operate at different speeds, just like those part time 4x4 system. So, it will only be a true 'permanent' 4x4 when the center diff is engaged through viscous coupling.

This in-turn leads to the question, Can we put mechanical lockers in permanent 4wd vehicles with viscous coupling center diff since it function like a part time 4wd drive under normal circumstances? And when it engages center diff, all 4 wheels are go. This is also similar to part time system when we engages both lockers when things get really slippery.

kingsonlim said:

hmmmm......ARB diff lock...........thats another dream......

Not gonna get one fitted as I wont be doing any extreme offroading in this classic

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Well, I am not doing any extreme offroading either - nor I'm going to - but here (Eastern Finland) in winter I have been stuck a couple of times. We can get a lot of snow occasionally. A rear lock (or a front winch) would have saved me from shoveling.

While we are on the topic of lockers, can I assume that lockers at the rear is okay, eg. air-locker like ARB or even Detroil style mechanical locker. But the front can only be fitted with selectable lockers like ARB's sirlocker while mechanical lockers such as Detroit are bad news???

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This is the impression that I've got. However, I would rather have a good winch in the front and not a front lock. Also I would rather have a rear winch than front lock. The front lock can have some serious effects on parts on the front axle (CV, the sticks) - if not used carefully. If you are into serious off-roading then the rear winch is much more useful than the front lock.

At least here, the first thing to invest is decent tyres, then rear diff lock or front winch and suspension. The front lock is really the last thing to put your dough into.

A question of thoughts:
Since Borg Warner is viscous coupling, technically the front and rear diffs are 'seperated', meaning they could operate at different speeds, just like those part time 4x4 system. So, it will only be a true 'permanent' 4x4 when the center diff is engaged through viscous coupling.

This in-turn leads to the question, Can we put mechanical lockers in permanent 4wd vehicles with viscous coupling center diff since it function like a part time 4wd drive under normal circumstances? And when it engages center diff, all 4 wheels are go. This is also similar to part time system when we engages both lockers when things get really slippery.

Click to expand...

I don't see why not. But I am not an expert.

Believe me....part of the reason I got this classic is to travel to your country, Finland. And of course, the neighbouring countries too.....

Would love to play a bit in snow too, but not anything extreme....

Still saving up for the suspension mod, rear locker or front winch....