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Thread: The mystery of the viscous coupling

  1. #11
    Join Date
    Jan 1970
    Location
    Douglas Park, NSW
    Posts
    9,264
    The VC in my daily driver & 'off roader' actually slips more than I would like. I was caught out climbing a rock face earlier this year with the front left wheel spinning.
    I'm still yet to work out if this is normal slippage or if I have a VC about to let go. I've tried replicating the situation in other spots but haven't managed to get stuck yet.
    Scott

  2. #12
    Join Date
    Jan 2016
    Location
    central coast nsw
    Posts
    43

    vc lock up

    hi guys i am in the same situation at the moment .turning on full lock you can feel it grabbing especially on tar with loose stone .I actually removed front shaft irarely offroad,although car seemed to roll ok in drive and not coming to ahalt on slight down hill grade ,when you say lock-up to me that means as if brakes on ,am i understanding correctly .normal h/way driving seems fine even with shaft in,am i being overly concerned and refit shaft as minimal offroad is done , looking for replacement vc in good condition but to yet no avail

  3. #13
    Join Date
    Jan 1970
    Location
    Avoca Beach
    Posts
    11,198
    The VC in my daily driver & 'off roader' actually slips more than I would like. I was caught out climbing a rock face earlier this year with the front left wheel spinning.
    From RRC experience I think this is quite normal and related to the open front diff more than the VC.
    However having said that , the feedback I have had over many years is that it is sitting at a rock with a front wheel spinning is the most damaging to the VC, as it has to "hump" ie rise in internal temperature until it locks.

    My VC was fine at 240Kk when I sold the car, ( and stupidly gave away a 80KK VC and another transfer with stripped splines with the car). I could have been RICH!

    I think the best help you can give a VC is to fit an Ashcroft , Quaife or other torque biasing diff to the front axle to minimize wheelspin and therefore front to rear speed difference.
    Regards Philip A

  4. #14
    Join Date
    Jan 2018
    Location
    Beechworth
    Posts
    4
    Thanks all for the info, feeling more comfortable now. I do like Quaife LSDs, however I don't think I'll be working it sufficiently hard to justify such an enhancement in the immediate future.

    I'm sure I'll be posting more questions as I get it back on the road and reliable.
    All the boots on the ball joints and tie-rods are torn, so they all need replacing.
    Any tips for getting the ball joints off or fitting them, my reading implies they are a press fit I've got good hammering skills, but sounds likes they won't help me here.

    Thanks

  5. #15
    Join Date
    May 2008
    Location
    Camp Hill, Brisbane
    Posts
    196

    Ball Joint replacement

    Best guide that I found was Michael Murphy's YouTube series:
    Swearing and Skinned Knuckles Episode #3: Land Rover Discovery Ball Joint Replacement Part 1 - YouTube
    Practically no difference between D2 and P38 for this task.
    You will have a hard time finding just the boots, although MR Automotive in Redcliffe, Qld may have them.

    Cheers,
    Steve

  6. #16
    Join Date
    Jan 2016
    Location
    Netherlands
    Posts
    232
    When researching to rebuild my VCU I came across some info that was dormant in the back of my head but I forgot to share with you. ie. I'm getting old and forgetful

    The VCU works by heating up the fluid inside. When warm it forces all the plates inside the vcu to stick together tightly and hence lockup your diff. This process is somewhat between digital and analog, ie. the system works by beeing on/off/on/off etc. often in a short time. The silicone oil heats up and locks, cools down and allows slippage and thus heats up and locks etc.

    This process wears the oil out. Also, silicone oil is not very good at lubrication, but then again that's not what we want, we want the darn thing to lock up Anyway, what happens is that abrasive particles from the discs mix with the oil and the oil "burns" over time which makes the VCU turn more difficult over time. From what I have read it is not quite linear but let's just assume for the sake of argument that it is.

    Putting all this info together: the VCU is a (like so many things on the P38 :P) maintenance part. It wears out. The silicone fluid can be replaced and when in time, thus before the unit is completely cooked, with new fluid can operate for a certain amount of time again. More usage of the unit; ie. in conditions where there is a fair difference between the front and rear axle, wears the fluid and thus the VCU out faster.

    I have started a thread with the question if others have rebuild theirs. Let's see if we have some people with experience over here. If not, we'll pave the way with info from the interwebs From what I can tell right now, replacing the fluid (in time) will not wear the plates out too much and we should be able to replace the fluid in our units multiple times before they give up and considerably lengthen the lifespan of the unit and thus the car

    -P

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