silly question perhaps, but..

Submitted: Sunday, Jan 09, 2005 at 11:59
ThreadID: 19203 Views:2270 Replies:7 FollowUps:6
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HI all,

I understand the concept and mechanics of only engaging 4WD on loose/slippery surfaces, so that diff windup can be relieved by slippage of the offending wheel/axle. Here's my question: I have taken my vehicle through some rocky sections of track, where 4WD Lo-range was absolutely needed, but being so rocky, there would have been not much (or even none at all) chance of wheel slip/spin, so...what happens to the diff windup? I don't have airlockers or anything, just standard drivetrain on my Prado so only talking windup in centre diff at this stage. If I put airlockers in, in rocky ground I would then be getting windup in front and rear diffs, wouldn't I?

Can anyone tell me its ok or not ok to drive my Prado over rocky ground in Lo range (centre diff locked) without destroying anything, or do I need to occasionally unlock the centre diff?

Any info appreciated.
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Reply By: Wayne (NSW) - Sunday, Jan 09, 2005 at 12:32

Sunday, Jan 09, 2005 at 12:32

Not a silly question but a hard one to put into words.

This is what happens when the vehicle is in 4WD mode, hi or low range it does not matter, and in the case of costant 4WD, with the centre diff locked.

Transmisson wind up(TWU) will not accure if the vehicle is driven on a hard flat surface in a straight line.
TWU will accure if the vehicle is turning on a hard flat surface.
TWU is created by the front wheels travelling at a different distance to the rear wheels, eg, doing a "U" turn.
TWU will not happen if the front or rear wheels can slip.
Slip can occur when the wheels are on a lose surface like mud,dirt, or sand.
Slip can also occur when one or more wheels leave the ground.

So to answer your question,
your vehicle can be safley driven over a rocky track in low range 4WD locked centre diff with out any damage to the transmission.

When I do the 7 day Vic High Country I am in 4wd mode for the 7 days either hi or low range and only take it out when I hit the black top, and on that trip there is a great variety of track condictions

Having some form of locking front or rear diff would mean that the wind up would accure in the axels as well as the transmission. Air lockers should only be used when the going gets tough and turned off as soon as possible.

AnswerID: 92033

Follow Up By: Rob from Cairns Offroad Training & Tours - Sunday, Jan 09, 2005 at 16:11

Sunday, Jan 09, 2005 at 16:11
Good answer to a tricky question Wayne. Cheers Rob
FollowupID: 350860

Reply By: Member - Davoe (WA) - Sunday, Jan 09, 2005 at 12:51

Sunday, Jan 09, 2005 at 12:51
Yep wondered the same thing the other day when I climbed a steep granite rock that needed L1 but there wouls have been no slip I guess too much of it would be detrimental but if there is a bit of loose gravel on part of the track that would help but otherwise could be a bit of a tricky one
AnswerID: 92035

Reply By: Willem - Sunday, Jan 09, 2005 at 16:31

Sunday, Jan 09, 2005 at 16:31
Just an aside.......
Most of the older type vehicles get gearbox windup when driven in Low Range for a period of time. When you stop and try and disengage the gearstick, it wont let go. With my GQ I reverse about 5 metres and then the lever slips back easily. THis has happened with most of the 4bies I have owned.
AnswerID: 92058

Follow Up By: Member - Davoe (WA) - Monday, Jan 10, 2005 at 13:12

Monday, Jan 10, 2005 at 13:12
got a meal off of a couple of girls on the grr like that. Got approached at some campgrounds asking If I had any mechanical knowledge coz they couldnt get their 60s out of 4wd - I was only to happy to help
FollowupID: 350980

Reply By: Kiwi Ray - Sunday, Jan 09, 2005 at 17:21

Sunday, Jan 09, 2005 at 17:21
Hi Rich.
Wayne answered your question well.
is not something that can be explained well, but the application of the various units of your truck, where and whe nto engage what only comeswith time and experience.
Perhaps I could suggest that if the track is just rocky but not too rough try leaving the centre diff unlocked, as long as you do not lift a wheel it will drive as well, plus you will learn to use the inertia to pass over small points that will get you cross axled.
The further you learn to drive with out all the extras will help you in the future, when you have them you will have a bettewr idea of when to use what.
I use all 3 diff locks most of the time as I find it is kinder to the truck, but there are cetain track conditions that diff locks a particularly the front is a hinderance to the truck and driving.
i do differ from a lot of people in that I lock all diffs on steep down hills, as this aids truck control and prevents one wheel from loosing traction
This is a big field to cover and a lot differs onteraine and vehicle type
AnswerID: 92064

Reply By: RichieK - Sunday, Jan 09, 2005 at 21:24

Sunday, Jan 09, 2005 at 21:24
Thanks for all the interesting replies! Re the response to leave centre diff unlocked, no can do in a Prado once in Lo range. I'm referring to a steep, very windy, very rocky, long uphill climb that didn't have much loose dirt/rock. The further up I went, the more I was expecting a big noise from the centre diff. Hard to stop halfway up and go into hi range to unlock the centre diff momentarily, reversing not an exciting option either, but I guess if this was a major issue, no one would be getting into the rough rocky stuff, diff-locks would be failing left, right, and centre (sorry, front, back and centre).

Thanks again - any further comments welcome!
AnswerID: 92092

Follow Up By: Member - Browny (VIC) - Sunday, Jan 09, 2005 at 22:23

Sunday, Jan 09, 2005 at 22:23

If your steep climb was a sharp no slip continuous turn (left or right) then there might be an issue, but being windy and rocky/undulating there's ample oppurtunity for the "wind up" to be alleviated, each time you change direction or one wheel is either lifted from the ground or has very little weight on it (allowing a slight amount of slip) then any wind up will be alleviated.

FollowupID: 350909

Reply By: RichieK - Monday, Jan 10, 2005 at 05:24

Monday, Jan 10, 2005 at 05:24
Gotcha Browny, I can see how that would sort out the windup occurring as a result of inside/outside wheels travelling further, but woudn't there still be an issue at the centre diff? The rear wheels won't travel as far as the front, on a windy climb.
Hope that the unweighting of certain wheels is enough to allow the slippage.

Cheers for the reply
AnswerID: 92114

Follow Up By: Wayne (NSW) - Monday, Jan 10, 2005 at 07:13

Monday, Jan 10, 2005 at 07:13

4WDrives have been out there for years and have not sufferd from too much windup. Wheels slipping will allow the whole drive train to unwind.

If there was no slipping and we all got 100% traction going up or down a hill then we would not need tread on the tyres, LSDs or Diff locks or even 4WD for that matter.

When the centre diff is engauged it is the same as locking the hubs on a Troopie and moving the little lever to 4H or 4L. The centre diff is easer to engauge by the press of a button but will do the same thing, split the drive 50% to the front 50% to the rear.

FollowupID: 350923

Follow Up By: Member - Davoe (WA) - Monday, Jan 10, 2005 at 11:04

Monday, Jan 10, 2005 at 11:04
yep wayne at the end of the day the drive trains arnt so fragile at the slightest hint of abuse they expire. The underground vehicles I have driven were rusted into l4 and couldnt be removed when being driven along the high grip haul road and bitumen from the portal to the office and they wernt doing diffs/tc/gearboxes on a daily basis
FollowupID: 350961

Follow Up By: bundyman - Monday, Jan 10, 2005 at 11:45

Monday, Jan 10, 2005 at 11:45
Yeah Rich,

We drive cruisers that are permanently locked in low range on concrete all the time with out a problem - this includes many full lock turns in workshops and fuel bays etc. You can hear the CV's coping a work out but you will also here the wheels spin (when driving slowly on full lock) even on concrete as the wind-up gets to much. When I say spin I mean .......argh its one of those things you just have to experience to get what I'm saying.

FollowupID: 350963

Reply By: Member - Karl - Monday, Jan 10, 2005 at 11:55

Monday, Jan 10, 2005 at 11:55

Good question you asked and I hope you got the info you needed.

If you are concerned about TWU a trick I was taught when doing my Off Road Cse with the Army was once you get back onto bitumen put the drivers side wheels on the bitumen and keep the passengers side wheels on dirt and drive in reverse for about 10 - 20m. This should help - it is similar to what Willem said.

Enjoy your driving.

AnswerID: 92165

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