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I supported Toymods
Location:
Perth, Western Australia
Registered:
December 2002
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Re: WANTED: R31 Skyline Differential
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Sun, 14 December 2003 16:07
 
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Got your PM Rex, thought I'd post here so everyone can read it!
Th R31 Skyline diff is a factory 28 spline disc brake diff that utilises alloy callipers, with a 7.5" crownwheel. The PCD is the same as many Toyota PCD's in being 4X114.3mm. The wheel studs are different however being M12x1.25, as opposed to the Toyota's M12x1.5 - this problem can be overcome by installing new wheel studs the correct pitch, or using the suitable wheel nuts to the pitch. The centre hub is also larger than a factory Toyota unit, so if you have dedicated Toyota wheels, you'll need to machine out the central hub receiver to suit the BW diff.
LSD's and ratios can still be bought brand new for the 7.5" diff, they can't for the earlier 7.75" diff (these diffs also run 25 spline axles, so make sure you are getting 28 spline axles). The LSD itself is a cone and race style unit, that by it's very nature - wears away the hard surface the cones grab to limit slip - ie, be careful buying second hand LSD units, many of them are stuffed through active use. You can check the effectiveness of used LSD's by measuring the force needed to turn a wheel while the other one is held still - check with Motive Gear (??? - Borg Warner's new name) for the exact force needed. An LSD unit is around $400+ brand new, and you can also buy Torsen LSD's to suit the diff - a much better option, as the BW LSD will revert back to a single spinner once hot, or on a very tight radius.
With the diff running an offset centre, several people I've spoken to about converting to early model Celicas, have stated that by using the original short axle, in the new "long side", you can get away with only having to modify (shorten) one axle during the conversion. I've not tried this as I usually have a set figure I work to, when converting diffs, but it may be accurate in length for you, with a Sprinter being wider in the diff than the RA28 I fabricated one for. The axles can also be cold splined, saving the need for any heat treatment after shortening, but it will stuff the splining tool - sometimes it's cheaper to buy a new tool than heat treat an axle(which is usually done on weight of the object).
New ratios are available, they are around $400 a set, or you can pull 4.1 ratios from Pintarras, 3.7 and 3.9's from Skyline, higher ratios from late model Falcons and Commodores, and lower model ratios from some commercial vehicles running the same diff.
Conversion costs to remove the old mounting points, shorten and install suitable mounting points will be around $800, plus LSD cost if you have to buy one, plus replacement bearings if you need them, plus any brake reconditioning costs also if needed.
if you have any more questions, ask away?!
Clint!
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