How does the diff lock switch work?

Hi All

I have searched but not quite found the answer. The diff lock seems to work OK all the linkages are nicely cleaned and greased but the dash light stays on after the diff lock is off, sometimes for a minute or two sometimes hours. A couple of hundred yards in reverse always clears it.

How\why does that happen - how does the switch work? is it just a plunger thats got a bit crap or is it symptomatic of something more serious? It all works at the moment, which is handy in the snow, I dont want to open a can of worms by tinkering

When it "sticks" on, it generally mean that you've driven on it on a good road surface (ie when you dont need diff lock) and it has begun to wind up.

I would avoid driving for ages with diff lock on, as it eventually will destroy your transfer box

quite useful :

How Diff Lock Works and When To Use It (UK Terminology) - YouTube

Perfectly normal to sometimes have to reverse a short distance to unlock diff lock

It's a mechanical linkage

thanks guys - so what your saying is Im being over entusiastic with the diff lock and even though I may have taken it back off, I've not done it soon enough so theres some wind up in the transmission and only when that wind up has been released does the switch move and the light go off.

Really good video by the way explains it all very well

gse1986 said:

When it "sticks" on, it generally mean that you've driven on it on a good road surface (ie when you dont need diff lock) and it has begun to wind up.

I would avoid driving for ages with diff lock on, as it eventually will destroy your transfer box

quite useful :

How Diff Lock Works and When To Use It (UK Terminology) - YouTube

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What exactly gets "wound up". I would have thought that one wheel turning slower or faster when they should both be at the same speed would snap or twist something imediatley, and driving in reverse would have no effect? It obviously does the trick but what actualy happens?

mick the builder said:

What exactly gets "wound up". I would have thought that one wheel turning slower or faster when they should both be at the same speed would snap or twist something imediatley, and driving in reverse would have no effect? It obviously does the trick but what actualy happens?

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Half shafts twist, pinion gear 'climbs' the crown wheels, tyre sidewalls can buckle at low pressures, lots of other minor issues all add up till something goes bang .. mostly the tyres slip and allow on-twisting, but if on tarmac and getting wind-up then it can go bang quite quickly.

Turning left, then right unwinds it, or vice versa. A constant turn one way would wind-up and go bang very quickly.

Paul D said:

Half shafts twist, pinion gear 'climbs' the crown wheels, tyre sidewalls can buckle at low pressures, lots of other minor issues all add up till something goes bang .. mostly the tyres slip and allow on-twisting, but if on tarmac and getting wind-up then it can go bang quite quickly.

Turning left, then right unwinds it, or vice versa. A constant turn one way would wind-up and go bang very quickly.

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I understand in theory but looking at it in laymans terms, if i bend say a metal coat hanger, no amount of bending it back will get it in the same shape as it started in and at the bend, the metal has weakened. Does that make sense?

mick the builder said:

I understand in theory but looking at it in laymans terms, if i bend say a metal coat hanger, no amount of bending it back will get it in the same shape as it started in and at the bend, the metal has weakened. Does that make sense?

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Yup, but totally different metals and metal compositions .. and a coat hanger has no joints like a gear train has. But yes, constant wind-up and wind-out will develop a set and will weaken the structure somewhere .. that's why you don't try to induce wind-up by using cdl only off-road or on slippery surfaces.

Paul D said:

Yup, but totally different metals and metal compositions .. and a coat hanger has no joints like a gear train has. But yes, constant wind-up and wind-out will develop a set and will weaken the structure somewhere .. that's why you don't try to induce wind-up by using cdl only off-road or on slippery surfaces.

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Thanks for the explanation.

diff lock collar has coffin shaped teeth and so the corresponding ring on front output shaft ,diff tube has straight splines ,the coffin shape means that once diff collar is slid over the output shaft any torque both forward or back pulls the collar greater into mesh as its not slid over a straight spline but angled teeth,wind up in transmission also puts torque onto collar as well as engine if collar had straight cut teeth it would just release without releasing any wind up but also would be prone to jump out of diff lock just when you need it

If you're in the UK at present, I imagine there should be some ice nearby where you can unwind it?