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  1. #11
    Join Date
    Apr 2004
    Location
    East Leake, Nottinghamshire, England.
    Age
    56
    Posts
    9,640
    Quote Originally Posted by Darnpistonbroke View Post
    This is interesting. I have never heard of this needing to be done. This could explain a couple of things with the history of my car. I built it back in the early 00's but had to sell it as importing it to Spain was a nightmare. The new owner 'bent' it quite a bit soon after ownership. He had it rebuilt but had a couple more excursions in it to add to the history.
    I bought it back of him three years ago and am now returning the car to how it should be. However I have never had any issues with how the car handles. Any waywardness of the back end to me have always been controllable, and predictable during a couple of instances where I have gone for gaps like a spanner.
    The diff is starting to leak so maybe time to get the thing off and dispatch it to a shop for overhaul and adjustments! Its a 3:3.07 PL.

    I drove my mates car without the diff having been derated and there is a very simple way to see if this is needed. On a quiet wide road where there is plenty of room and visibility, drive around the bend and half way around accelerate fairly hard but safely. If the car tries to straighten up and stop turning this is down to the diff needing de rating. Scared the hell out of me when this happened as we nearly crashed, it had also happened to him which is why I was driving his car at the time.
    Martin

    351W 416.7 HP and 466.8 ft-lbs

    Running Mega Squirt and Edis 8


  2. #12
    Join Date
    Oct 2018
    Location
    Shipston-On-Stour
    Posts
    618
    I have heard people say both options are fine, de-rated or as is. My diff (2.88 lsd) has never been touched. As far as I remember (!) it came out of an XJS but can’t be 100%. It was well over 30 years ago. (A mate was working for a jag specialist at the time). I can honestly say I have never (famous last words!) had a handling issue with it. Not saying it doesn’t happen, just not experienced it.
    It would be interesting to know how many untouched versions are running happily out there and how many have had handling issues with standard ones.
    Flagged up as a potential safety issue I can understand why people make the effort and spend the money but is it really necessary? I genuinely don’t know.
    I do spend money on top drawer tyres. Could it be that one cancels out the other????

  3. #13
    Join Date
    Oct 2018
    Location
    Shipston-On-Stour
    Posts
    618
    Quote Originally Posted by TINKA View Post
    I drove my mates car without the diff having been derated and there is a very simple way to see if this is needed. On a quiet wide road where there is plenty of room and visibility, drive around the bend and half way around accelerate fairly hard but safely. If the car tries to straighten up and stop turning this is down to the diff needing de rating. Scared the hell out of me when this happened as we nearly crashed, it had also happened to him which is why I was driving his car at the time.
    Ah, missed your post while writing mine. Interesting. Mine is fine. Odd why some do and some don’t but I get the test, that would be pretty useless!!

  4. #14
    Join Date
    Aug 2007
    Location
    Bournemouth
    Posts
    622
    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.
    David.

    Life is driving the Cobra. The rest of the time is just waiting................till I fix it!

    Wessex region caretaker rep.

  5. #15
    Join Date
    Dec 2007
    Location
    cheshire
    Posts
    1,419
    All I can say is, never had an issue with my 3:31-1 open diff but it was knackered with noisy bearings and some wishbone type thing inside was snapped! I picked up a 2.88 PL on EBay and Russ on here rebuilt it - he derated it and it is awesome! Zero noise and I have given it loads with not a single issue, I cannot recommend Russ enough- really pleased.

  6. #16
    Join Date
    Oct 2018
    Location
    Shipston-On-Stour
    Posts
    618
    Quote Originally Posted by 427jlc View Post
    All I can say is, never had an issue with my 3:31-1 open diff but it was knackered with noisy bearings and some wishbone type thing inside was snapped! I picked up a 2.88 PL on EBay and Russ on here rebuilt it - he derated it and it is awesome! Zero noise and I have given it loads with not a single issue, I cannot recommend Russ enough- really pleased.
    Who is Russ? I may one day get around to having mine rebuilt (and possibly de-rated!!).

  7. #17
    Join Date
    Feb 2011
    Location
    Northampton
    Age
    42
    Posts
    4,783
    russell_ram on here - also did mine.. though I can't report on success yet for obvious reasons!
    My DeDion build diary..
    Hon Sec of the Digidash branch of the Unpopular Kit Car Design club

  8. #18
    Join Date
    May 2004
    Location
    Cowbridge, United Kingdom
    Age
    63
    Posts
    10,315
    Russell_Ram2 in fact.
    Also the Treasurer of the UKCC.
    Kev Davies
    South Wales Area Rep. UKCC Membership Secretary
    DAX Mk4, 383 Chevy Stroker, Tremec. SOLD
    Contemporary CCX 3-4028, 445ci Big Block FORD FE,TKO 600, Old School IVA'd and SOLD
    Dax De Dion LS2 and T56 IVA'd June '17 SOLD
    1965 Ford Mustang 289 Convertible SOLD
    In build- Hawk 289 Sebring Awaiting IVA

  9. #19
    Join Date
    Feb 2011
    Location
    Northampton
    Age
    42
    Posts
    4,783
    Well .. I was close
    My DeDion build diary..
    Hon Sec of the Digidash branch of the Unpopular Kit Car Design club

  10. #20
    Join Date
    Mar 2007
    Location
    Maldon Essex
    Posts
    536
    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

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