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Thread: 4wd for tarmac explanation

  1. #1

    4wd for tarmac explanation

    Quick one for the mechanics

    Wasn't until recently that I learned you can't just take any Jeep or 4wd and stick it into 4H from 2H. And drive as it can "wind up" the transmission due to say not being slippy enough

    Example was my old ford maverick loved it but no use 4H on tarmac in snow unless very slippy

    What allows you to drive on road in 4H ? Is it a limited slip diff ?

    Paul

  2. #2
    Transmission "wind up" can happen with any transmission that doesn't have an open differential

    Any vehicle not designed to travel on tarmac if in 4WD is flawed...so yes, this probably does happen in a Jeep

    Only when engaging the diff lock and travelling long distances can you wind up a proper 4WD system
    you get a certain amount of "wind up" even without though
    This can be felt when at full lock in 4H or similar when doing tight turns on tarmac.
    Quattro's do this all the time but its not enough to damage the system or scrub tyres

    old defenders often get stuck with the diff lock "on" but can be coaxed out with some reversing and

  3. #3
    No it is a centre diff which allows the front and back axles to turn at different speeds. Any vehicle which is permanent 4wheel drive has to have this.Wind up on part time 4wheel drive can seriously shaft the transfer box. With an ordinary diff it is possible to lose all traction on one wheel, a limited slip diff has a set of friction plates which partially lock when one wheel loses traction so that drive is transferred to the other wheel. On black ice it is all academic.

  4. #4
    the straight forward/backwards isn't so much that hurts you... It's the turning on a solid surface that is really noticeable and can cause damage because the inside wheel rotates at a slower speed than the outside one.... best thing going now is the AWD's...

  5. #5
    It's more about whether the 4x4 has a centre diff' or not. A centre diff' allows the front, and rear wheels to turn at different rates to each other, the same as the front/rear diff's allow the near/off side wheels to turn at different speeds.

    I have the VW Amarok, and it doesn't have a centre diff', so whilst you can run it in 4x4 on tarmac, it doesn't like going around tight, slow corners/bends, so on the road, I just run it in 2WD, which is more than adequate, given the electronic traction control, and is also more fuel efficient.

    For off road/snow, I just switch it into 4x4, with the option of low ratio, & locking the rear diff', if required, and the hill decent has been pretty useful too.

    Anyway, if you feel your "truck" needs 4x4 on tarmac (you really don't with modern technology) make sure the 4x4 has a centre diff'.

  6. #6
    Regular Poster Robb's Avatar
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    Quote Originally Posted by sauer View Post
    Quick one for the mechanics

    Wasn't until recently that I learned you can't just take any Jeep or 4wd and stick it into 4H from 2H. And drive as it can "wind up" the transmission due to say not being slippy enough

    Example was my old ford maverick loved it but no use 4H on tarmac in snow unless very slippy

    What allows you to drive on road in 4H ? Is it a limited slip diff ?

    Paul
    No its not the limited slip diff its the centre diff in the transfer case of the gearbox, Not all 4x4's have a centre diff hence why you shouldn't really use 4wd on the road as you have recently found out. Basically you have a diff in each axle which allows each wheel on that axle to turn at a different speed, a centre diff allows the wheels on the front and rear axle to turn at different speeds independently of each other.

    BLIMEY By the time I wrote this out 3 more posts have turned up..! +1 What Lateral said.
    Might be a case of too much information but have a read of this http://www.google.com/url?sa=t&rct=j...59930103,d.ZGU
    Last edited by Robb; 26-01-2014 at 16:46.

  7. #7
    Quote Originally Posted by Robb View Post
    Not all 4x4's have a centre diff
    As I said..
    All the GOOD ones DO!

    a 4WD system without an open centre diff is at such a disadvantage

  8. #8
    Quote Originally Posted by bewsher500 View Post
    As I said..
    All the GOOD ones DO!

    a 4WD system without an open centre diff is at such a disadvantage
    And why is that ? There are 4x4's that are designed specifically for the road, generally "road cars", such as the Audi's, etc', where they are designed to driving at much higher speeds than you are going to be diving a track at ! Then you have 4x4's that are designed mainly for the road, but with off road ability. These will always be a compromise, but do a very good job for their intended purpose.

    Then you have 4x4's that are specifically designed to spend the vast majority of their time off road such as the Land Rover/ Defender type 4x4. Sadly, the designers got a little confused by the remit "off road", and took it a little too literally, where that's where most of them spend, most of their time, "off the road"

    Joking aside, you don't need 4x4 on the tarmac, in a truck running off road tires, where the tires traction will give up way before the 4x4 system ! "Traction control" is far more useful.

  9. #9
    "you don't need 4x4 on the tarmac" heh heh but they do have some awfully steep driveways in Guildford!

  10. #10
    Not sure how the law is nowadays, but 4WD used to allow towing of much more than 2WD, even if only 2WD was engaged. Old Landrovers were terrible for winding up, until they copied the third diff arrangement of the Range Rover.

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