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  1. #1
    Join Date
    Feb 2003
    Location
    Horsham, West Sussex, UK.
    Age
    59
    Posts
    195

    Richard's Dax Mk4 Build- The Differential

    The continuing story...

    Swapped out the differential for a better ratio (3.31 vs 2.8. Now comes the difficult part, fitting it all back. It's the Jag XJS/XJ6 IRS setup.

    I shimmed the fulcrum shaft brackets equally left and right at the front and equally left and right at the back. Leaving me with the correct width for the fulcrum shafts at the front to slide into the chassis while allowing the differential spreader plate to fit over the shafts at the back. Offered up the differential and fixed the top mounting bolts to the diff mounting plate. Problem. The threaded parts of the fulcrum shafts will go into the chassis, but the main/smooth part of the shafts won't. They are both too far to the off side and too far below the chassis holes. They both foul at approx the 4-5 o'clock position. So, if we assume the differential is machined perfectly (probably not the case anyway) then the differential mounting plate is angled slightly too far down at the front and pointing slightly to the off side of the car.

    Solution so far. I've added 3, 7 thou shims between the diff and the mounting plate for the rear bolts. That angles the diff up slightly at the front. Then I've taken shims out of the off side front fulcrum bracket and added them to the near side front bracket. And done the same to the rear shim packs. Now, if you torque up the top diff mounting bolts, the smooth part of the fulcrum shafts will engage in the chassis about 8mm or so, while allowing the differential spreader plate to fit at the other end. They won't go further in as its still not perfectly aligned. But the engagement may now be good enough. My guess is that having done the same for both sides of the diff I have corrected for the mounting plate offset while maintaining correct 30' toe in alignment for the rear wheels. I suspect a better alignment could be obtained by adding a pair of shims on top of the differential between the diff and the mounting plate for the front 2 bolts and the same for the rear too. That will drop the diff down a fraction more.

    Has anyone else had to go through such hoops to get the right alignment?

    It's all good fun though!
    Regards
    Richard

    Dax - Standard Chassis, a boot full of parts, Chevy 383 Stroker and Tremec TKO 600. Time for paint!

  2. #2
    Join Date
    Aug 2014
    Location
    York
    Posts
    468
    Richard, it’s a while back, but I don’t remember having much trouble with this; perhaps I was lucky. I set up the rear toe using the Dax supplied spacing tool and then manoeuvred the lump in to position using a jack. Hope you get something you are happy with.

  3. #3
    Join Date
    Feb 2003
    Location
    Horsham, West Sussex, UK.
    Age
    59
    Posts
    195
    It does seem strange to have to go through such efforts.
    If you loosen the top 4 diff mounting bolts by a turn or so it drops the diff down into perfect alignment vertically and with the shimming of the fulcrum shafts as described above I can correct the diff mounting plate offset to the drivers side.
    I'll do another trial fit once the new caliper shims and bolts arrive and I can set up the diff for mounting.
    If I get the perfect fit I'll leave it in place and fit the wishbones while the diff is attached to the car.
    More to follow...
    Regards
    Richard

    Dax - Standard Chassis, a boot full of parts, Chevy 383 Stroker and Tremec TKO 600. Time for paint!

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