Originally Posted by EvilChief
The good old BW 8-3/4" Differentials (solid axle only)
Any BW diff prior to EA had a different housing and center, but same same diff gears as newer BWs.
Housings between E-series Falcon, A-series Falcon, Commodore Vl - VS and R31 Skyline are different in terms of tube length, but housing is the same, hence any center carrier (open or LSD or spool) is the same right across the above mentioned models.
The axle splines are determined by the guts of the centers, regardless of Open, LSD or locker. VP, VR VS (possibly VN), R31 and most Falcons run 28spline axles.
The carries between Open and LSD are different and are not interchangeable, as the LSDs are "friction cone" based with a spring loaded center, where as the opens use spider gears with pins, however these are again identical across commodores falcons and skylines and are interchangeable. (Note to "tighten" LSD centers, shims under the center springs increase the cone pre-load, which retains the LSD in locked position and rises the break away friction load, to do it on the cheap regular washers can be used instead). (Please note there are aftermarket LSD options available that are not friction cone based, but come with their own carrier specific to their design).
When changing any component within a differential they must be re-shimmed. First off the pinion needs to be shimmed, in order for the pinion and crown to mesh on the full face of each other. If the pinion is not shimmed out correctly (not enough) then it will run on the toe of the crown and whine. If its shimmed too far out (too many) then it will run on the heal and once again whine. Either way it will lead to premature failure of the diff, by destroying the teeth on either the crown or pinion. It is imperative that they are shimmed so that the pinion contact surface is exactly in the middle of the crown contact area (use engineering blue to test). This may require several removals and re installations of all components to get right and is quite labor intensive.
Ensure to set preload on pinion when making up pinion nut (crushing the collapsible ring). There are tools available that will measure the preload based on the friction of bearings against their seating cones, or you can do it by feel. It should feel fairly firm with some effort to turn, but without nodging or hanging up.
Now the crown needs to be also shimmed in order to set the backlash. Determine the overall width off the original diff center including shims, bearings, cups etc, when fitted to housing, and compare that to the new overall width of the new center, if one is being fitted, if old center is reused, usually the shims are still correct, just mark right and left accordingly). To determine the backlash, use a dial gauge to determine the free play (rocking crown forwards and backwards and forwards with pinion stationary and observe gauge. Off the top of my head this should be between 7 to 11 thou. Adjust shims until this achieved.
A possibly usefull or useless fact, R31 manual Skylines ran 3.7 differential that will also fit falcons and commodore BWs and ran 28 spline axles centers. This is actually my most favorite diff ratio in all my Falcons, as they are common and cheap.
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