4wd & Transmission Wind Up

So, transmission wind up. I understand what it is, tension built up in the transmission components when the energy is stored (a bit like a clock spring) and continues to build up until some thing gives. Usually happens when the diffs are stopped from doing their job i.e. when diff lock is engaged on tarmac and the wheels cannot slip to compensate for differences in tyre diameter or one wheel going faster than the other around a bend for example, so I’m happy with this one…. Unless I’m wrong in which case please correct me!

My questions, which show my fundamental lack of understanding of diffs and 4wd are;
With diff lock disengaged:

• The diffs should be working so why is there a fuss over fitting one new tyre (larger diameter) with a part worn one on the same axle? (Which I have done before I was made aware there may be a problem – bugger!)
• Is 4wd true 4wd in that is power is applied to both wheels on the same axle equally all the time, or is it only applied to 1 wheel at a time and the diff allows the other to slip. In other works, you have 1 driving wheel on the front axle and one on the back at any given moment in time?

It’s a Defender hard top TD5 by the way.

ask stig, hes an eggspurt about diff wind up

yella said:

ask stig, hes an eggspurt about diff wind up

Click to expand...

Cheers Yella, sent Stig a message, see what he ses.

With diff engaged the back and front axles are driven equally - however the diff in the axle can allow ONE wheel to move if the other is stuck or most often if one is in mud or something and the other is in good contact with the ground the one in mud will spin.

So there is always power fed to all the wheels all the time, diff or not, the diff lock locks the centre diff so you get back and front drive.

So you do get one wheel an axle driving IF there is an uneven surface being crossed otherwise they are all being driven more or less - there are some differences obviously such as cornering.

Look on how stuff works, they have a good explination and animations!

discomania said:

So there is always power fed to all the wheels all the time,
!

Click to expand...

no there isn't

I should probably have written that better -

In that there is drive to the diffs which then apply it to the wheels - however the drive doesn't actually always make it to all 4 wheels all the time but the possibility is there if the traction is available.

I tell you this explination is better when I can wave my hands about and use sticks and things...

Many thanks for the help fellas, had a look at "how stuff works" last night and was still a bit confused but Stig has responded today with a good clear explanation which coupled to what I understood has got everything straight for me. Once again, thanks for the help. See below;

tyres are not an issue on the same axle as the diff compensates for the difference (obviously better practice to have both the same rolling radius). The front and rear axle are independant of each other until the central diff is locked, this will only provide direct drive to one wheel on each axle in the event of being completely stuck (the idea is not to get in that situation), but saying that you can fool the diffs into locking by applying some pressure to the brake pedal.[/I][/I]Stig

...........it also explains what a spam was doing fitting air lockers to his diffs on a different site I was looking at (or was it a magaazine, not important!). I didn't understand why he would want them if he already had a diff lock function on the vehicle but as Stig explains, that only locks the centre diff to get the front and rear axles working together.

........ and taking the advice and thought further, if I understand fully, that would mean that it may be possible to get out of a front and rear spin situation by a couple of gentle taps on the brake to lock the diffs and gain a couple of inches back onto something the wheels can grip on. A whole new world opens up in front of me!!!!! Excellent forum!

"Knowledge dispels fear"