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Thread: Defender diff lock problems

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    Default Defender diff lock problems

    Has anyone any ideas on how to resolve a problem with what appears to be the diff lock locked in. My Defender failed its MOT due to the fact it wouldn't stay on the rolling road, and kept backing itself off. The rear wheels where on a set of rollers at the time.

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    Default Re: Defender diff lock problems

    Quote Originally Posted by landie68rover View Post
    Has anyone any ideas on how to resolve a problem with what appears to be the diff lock locked in. My Defender failed its MOT due to the fact it wouldn't stay on the rolling road, and kept backing itself off. The rear wheels where on a set of rollers at the time.
    I'm confused. Let me get it straight. The rear wheels were on a rolling road, turning forwards I assume, and the vehicle kept going off backwards? That makes me think the front wheels were turning backwards when the rears were turning forwards, which doesn't sound like a diff lock issue. When the diff is locked both axles turn the same way at the same speed.

    If the engine was off and the truck was in gear and the diff was doing it's thing properly, that just about would make the axles go in opposite directions, but no tester is going to test brakes with the engine off. So, as I say, I'm confused.

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    Default Re: Defender diff lock problems

    You want to take it where I take Daisy.........

    Thet simply ask whether the brakes are OK and I reply 'perfect' and the matter is settled at that.

    Simples.

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    Default Re: Defender diff lock problems

    I hope ALL the wheels were on a rolling road at the same time or you are going to end up with serious axle wind and if not then the test has not been done properly ,our mot man hasnt got a 4 wheel roller so has to take it for a drive to test the brakes with a reader in the footwell
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  5. #5

    Default Re: Defender diff lock problems

    The engine was running at the time, it was after all a brake test, and I do not believe he had it in gear. The front wheels were on the rolling road, whilst the back wheels were on a set of rollers, when the LR reversed itself off, presumably with the front wheel doing the driving. Must admit it did confuse me as to how, but the tester indicated that the diff must be locked in. I happen to live in France, so they only recognise the rolling road as a test for the brakes. I suppose worst case scenario I can drop the front prop to get it through and replace it afterwards, but I would prefer to cure the problem rather than find a solution to passing the mot.

    Any thoughts are most welcome.

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    Default Re: Defender diff lock problems

    Your Defender is perminent 4x4. So should not be tested on a single roller.
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    Default Re: Defender diff lock problems

    There's a lot of incorrect/incomplete information above.

    If you have the LT230R that's standard then without the diff locked it is quite OK to roller test it with a 2 wheel (single axle) brake roller. It will not damage it at that speed. Range Rovers with the Borg Warner chain drive box and viscous coupling are different as the viscous coupling makes the centre diff effectively locked for the purposes of this discussion.

    All vehicles WILL pop off the brake rollers* - that's the limiting factor, especially if the other axle is on free rollers. It's not a failure, it's a sign that the brakes are working. It's much worse when doing the handbrake compared to doing the service brakes as you don't have another braked axle trying to hold it still as the powered rollers try to move it backwards - and I note from the above that it was the back axle on the rollers. The back axle doesn't have a lot of weight on it and will lift out of the rollers a lot easier than the front.

    Just to put things in perspective, at my last test the handbrake only gave 439kg of braking, while the service brake gave 688kg - the difference being that when testing the service brake, the front wheels were trying to hold the vehicle in the rollers. In both cases, the limit was when the wheels just lifted out of the rollers. By contrast, I had a play on a 45˚ slope recently, and the handbrake would hold it with the rear wheels just on the point of slipping - so that's around 1400 to 1500kg of braking effort. It would be interesting to re-do the test with the static axle chocked.

    * At least if they are nice and grippy like the new set my local place has just got in.


    The only ways to have the vehicle reverse off the rollers are :

    1) The brakes are working and the rollers simply push the vehicle back as above.

    2) The main gearbox or transfer box is locked up - in which case the act of rolling the rear wheels forwards will turn the front ones backwards, assisting the normal tendency to jump off the rollers. But in this case, you wouldn't have driven it onto the rollers in the first place, or off again afterwards.

    If the centre diff was locked, then the front wheels would try and pull the vehicle forwards as the rollers turn the rear wheels.


    My advice, take it somewhere that's "got a clue" - if it passes with flying colours then consider whether to report the first place to the DFT. Be aware that if you do this, then the DFT may well want to retest your vehicle so be sure it really did pass with flying colours and was tested properly.
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