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  1. #1
    Join Date
    May 2014
    Location
    Birmingham
    Age
    42
    Posts
    719

    Jaguar Powr-Lok differential JLM11875- Re-build and de-rate

    Hi All,

    Well one of my winter upgrades will be a 3.27:1 power-lok diff.

    I wanted to ask how hard is it to rebuild & de-rate the diff for our Cobras?

    Not that i'm adverse to paying for this, its a job i would like to do myself as i originally rebuilt my own diff (Currently a 3.54:1 open).

    I really need to know about the de-rating bit, i understand that this needs to lower the locking vs weight but how to go about this is beyond me currently.

    Am I adding or removing the friction plates, or using different thickness's?

    Thanks in advance,

    Alan.
    AK Gen II delivery date Oct '15
    IVA pass Dec '18.
    On the road Jan '19
    GM LQ4 364ci, LS9 cam, Omex 710.
    Tremec T56 Terminator.

  2. #2
    Join Date
    Sep 2010
    Location
    Nova Scotia
    Posts
    813
    As far as I can tell, the Dana/Spicer Powr-Lok is essentially the same thing (although I'm not sure.. I'm still looking into this myself as I am considering a tear-down). The following info may be helpful:

    Here's a Service Manual that explains the re-orientation of the clutch discs from 5 contact surfaces to three (pages 8 and 9):

    https://media.spicerparts.com/cfs/fi...store=original

    Here's a Service Bulletin that has 8 pages you can link to including how to test the Limited Slip properties by making a torque measurement while rotating one wheel with the other locked (page 6, test "a"):

    https://www.cj3b.info/Tech/SB500PowrLok.html

    Finally here's some info with an expoded view of the differential at the bottom of the page:

    https://www.cj3b.info/Tech/SB500PowrLok.html
    John

    “A prudent person profits from personal experience, a wise one from the experience of others.”

  3. #3
    Join Date
    May 2014
    Location
    Birmingham
    Age
    42
    Posts
    719
    Really helpful John, thank you.

    Let me know if your brave enough to tackle this yourself!

    Regards,

    Alan.
    AK Gen II delivery date Oct '15
    IVA pass Dec '18.
    On the road Jan '19
    GM LQ4 364ci, LS9 cam, Omex 710.
    Tremec T56 Terminator.

  4. #4
    Join Date
    Oct 2010
    Location
    kent
    Posts
    57
    I’ve just changed the ratio on my Dax it was a 2:88 and went for 4:09 never done it before and as long as you keep to the tolerances it was straight forward, had to remove the whole rear axils which entailed cutting an access panel in the boot so the top bolts of the diff could be undone used a couple of trolley jacks and knocked up a cradle so it would stay upright when lowering it from the car once down you can separate the the diff and either swap it or change the crown and pinion. Lots of companies sell the shims and loads of videos helped me and just a reverse process to install and so pleased had no issues. Regards Andy

  5. #5
    Join Date
    Sep 2010
    Location
    Nova Scotia
    Posts
    813
    Oops, that last link was incorrect. Here it is:

    http://www.erareplicas.com/427man/jagrear/parts.htm

    Yes, I don't think working over the differential would be all that bad. I discovered my issue by accident. I had the car in gear with the right rear wheel on the floor and the left rear wheel in the air. I checked for play and there was this metal crunching sound when the wheel was rotated all the way forward in its range of play. The other side did not do this.

    I can't hear the noise when I drive the car and everything seems fine. I can sometimes barely detect a slight click when I start to move from a dead stop, but it sounds more like a brake pad click.

    The sound seems to be coming from just inside the differential where the stub axle goes in. I suspected it was just normal play in the V-notch for one fo the cross-shafts, but am no longer so sure after I saw this picture:



    I did the torque test in the second link and it seemed fine. So although I don't appear to be having a problem, I may take things apart over the winter because I'm curious.
    John

    “A prudent person profits from personal experience, a wise one from the experience of others.”

  6. #6
    Join Date
    Jan 2006
    Location
    Chelmsford Essex
    Posts
    818
    Quote Originally Posted by andybaz View Post
    I’ve just changed the ratio on my Dax it was a 2:88 and went for 4:09 never done it before and as long as you keep to the tolerances it was straight forward, had to remove the whole rear axils which entailed cutting an access panel in the boot so the top bolts of the diff could be undone used a couple of trolley jacks and knocked up a cradle so it would stay upright when lowering it from the car once down you can separate the the diff and either swap it or change the crown and pinion. Lots of companies sell the shims and loads of videos helped me and just a reverse process to install and so pleased had no issues. Regards Andy
    Hi Andy
    Interesting on your thoughts since a large jump in diff ratios from 2.88 too 4.09. I am running a 2.88 LSD and looking at a winter swap out or rebuild. A good time to change ratio's. I do like the low 2,000 RPM at motorway speeds in fifth and never have to change down as I have so much bottom torque.

  7. #7
    Join Date
    Jan 2004
    Location
    Southwest, Somerset, U.K.
    Age
    35
    Posts
    3,193
    Just send it to Ben at simply performance. It will get done very quickly, cost not much more than buying the parts yourself and will come back set up to the correct tolerances and derated settings along with a warranty

    Simply bolt it back in.

    I use them for all our turnkey build axles and parts.

  8. #8
    Join Date
    Sep 2009
    Location
    Leeds
    Posts
    2,871
    RussellRam does this as well i believe - rebuild and de-rating that is
    Conny - A Carnival Red Metallic (paint code Ref: Jag CGG/1811) Southern Roadcraft V8 ( SRV8 ) with 383ci stroker chevy.

  9. #9
    Join Date
    Jan 2014
    Location
    High Wycombe
    Age
    55
    Posts
    583
    What would be the main disadvantages of leaving a PL as it is, ie not having it de-rated? I have a Dana diff' on mine and surprisingly it's a 2.87 not a 2.88 as most of the Salisbury's are. The car won't be on the road for some time yet so it can stay where it is for now (fitted and in place) and I definitely don't have the budget to change anything just yet. It will, some time soon, be connecting to the Lexus engine and auto gearbox.

    Any thoughts, Graham.
    AK gen 1 delivered 05/05/17, on the road shortly!

  10. #10
    Join Date
    Feb 2011
    Location
    Northampton
    Age
    41
    Posts
    3,875
    It will stay 'locked' until a much higher torque differential is reached, with a car several hundred kilos lighter than the original application that could result in the diff remaining locked through a corner and attempting to push you off the road or, worse, unlocking and then inappropriately locking mid-corner and attempting to split you off the road backwards.. that's the theory, anyway.
    My DeDion build diary..
    Hon Sec of the Digidash branch of the Unpopular Kit Car Design club

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