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  1. #21
    Join Date
    Apr 2004
    Location
    East Leake, Nottinghamshire, England.
    Age
    56
    Posts
    9,640
    Quote Originally Posted by JamesB View Post
    The clutch packs wear over time, so if you took a PL straight out of a donor car and put it in a Cob then there is a good chance that it would have "de-rated" itself over time and you would not have any problem with it. If you then rebuilt the diff with the original no of clutch packs then that's when you would suddenly find that you had a problem or if the donor car had a really good diff in it. But fundamentally the Jag diffs are designed for a much heavier car and there for the limited slip can be more effective in the heavier car without causing it to want to straighten up too much. Ward rebuilt mine, a 3.31 PL and de-rated it at the same time
    I de-rated my own diff and all I can say is using a torque wrench it went from about 95flb when I started to break the lock to about 25flb when I had finished.
    Martin

    351W 416.7 HP and 466.8 ft-lbs

    Running Mega Squirt and Edis 8


  2. #22
    Join Date
    Mar 2007
    Location
    Maldon Essex
    Posts
    536
    Yes, I would have done the same but I needed a fair bit done, bearings seals etc etc so I just got Ward to do it. I do think that it's probably quite important to do this though. I am guessing that most who have no problems have a worn PL, that needs to be considered before rebuilding one to original spec and shoving it back in a Cob.

  3. #23
    Join Date
    Aug 2004
    Location
    Christchurch, NZ
    Age
    60
    Posts
    2,503
    Quote Originally Posted by Darnpistonbroke View Post
    Well the last time it happened to me was Christmas Eve. Came out of a side turning going for a gap and also to beat some traffic lights. As in my previous post, looking back I was probably a bit of a spanner. Anyway, the rears lit up and I had to steer into the drift. Fortunately I know how to drive and didn't release the power all at once. Otherwise I could have ended up snaking it followed by a tank slapper.
    I may have looked pretty impressive to anyone half my age but I felt a little foolish both during and after. The thing is, I got away with it! The next time could be different.
    I would not have happened in my Audi.
    This is expected behaviour for an LSD - the diff locks, the tyres break traction and you (probably) get some oversteer; it's not related to preload. Or did I miss your point?
    Cheers

    Myles D-W

  4. #24
    Join Date
    Jan 2006
    Location
    Chelmsford Essex
    Posts
    1,631
    James your spot on with the wear on the PL clutch plates and rating changes with wear. I picked up a 2.88PL with 43k miles on it and tested the breakaway torque and it was 23-25ilbs . So it had lost fiction. The crown and pinion mesh pattern were spot on as well as the back lash so did not need a rebuild. I did wonder without taking it apart the set up of clutch plates in the LSD. Does this mean that a derate PL diff needs a rebuild to keep.it in the correct torque band as the plates wear.

  5. #25
    Join Date
    Mar 2007
    Location
    Maldon Essex
    Posts
    536
    In theory yes but I suspect that the less plates (de-rated) means less pressure means less wear and therefore a de-rated one may be expected to last a bit longer within a reasonable spec. Also if you are driving on a surface that has relatively even levels of grip, i.e tarmac, then you will only need a moderate level of LS effect as both wheels should loose traction at a similar point. Therefore if the diff becomes a bit worn it should not really matter in these cars.

  6. #26
    Join Date
    Apr 2012
    Location
    swansea,south wales
    Age
    57
    Posts
    194
    Just wondered how to test my diff I jacked one wheel up and got no noticeable resistance with the transmission in neural does this mean my lsd is dead and if so shouldn’t be giving me my problem

  7. #27
    Join Date
    Mar 2007
    Location
    Maldon Essex
    Posts
    536
    No, not really, firstly to test function, jack it up, at the rear with both wheels off the ground, leave it in gear and rotate one wheel forwards, the wheel on the opposite side of the car should also rotate forwards if the lsd is working as an lsd. If not then the opposite side wheel will rotate in the opposite direction.

  8. #28
    Join Date
    Mar 2007
    Location
    Maldon Essex
    Posts
    536
    Sorry, I meant leave it out of gear!

  9. #29
    Join Date
    Apr 2012
    Location
    swansea,south wales
    Age
    57
    Posts
    194
    Jacked both rear wheels up and when turning one the other turns the same direction but if I hold one still I can still turn the other withe little resistance so I’m guessing the power lock is worn out

  10. #30
    Join Date
    Mar 2007
    Location
    Maldon Essex
    Posts
    536
    Yes, fooked, but given your other noises I would suggest that something worse is likely to be wrong.

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