1) third motion holder
always a pain to try and hold in a pair of soft jaws, particually when you are chasing the detent plungers round and round (just a bit more, just a bit more, click! - damm!
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its a bit of chunky box section with a hole drilled through it (so the third motion can locate in it) - it has a pinion welded to one side, and a 3rd/4th inner hub welded on the other.
one way
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and the other
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for extra points use a 'distressed' pinion!
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2) diff holder / checker
a multi use tool this one.
the base part lets the diff be held securely in a vice, with no damage, so any diss-assembly / re-assembly job can be done. its made from a pot joint thats been slotted to allow a thick bit of steel plate to be welded into it - if your making one of these, its important to keep the welding heat away from the splines in the pot joint as they will nip up if you get too close and make it impossible to slide the diff output into the pot joint (that was the failing of my version one!). any sort of diff will fit this, if you punch the little 'core plug' out the centre of the pot joint the earlier outputs will fit fine into it.
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the upper part hold the other end of the diff and locks it solid, so that the crown wheel bolts can be undone / done up - the 'legs' locate slackly in the box section 'sockets' of the lower part - this allows a little bit of 'slop' which is needed when rebuilding an lsd (as per photo), its not so vital if your only doing std diffs.
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finally, the third part of this tool, is the stub of another pot joint that has the nut welded from a clutch release bearing boss onto it - this slips onto the output of an lsd and allows the testing of the break point of the plates with a torque wrench.
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both these tools work great, there is no danger of any damage to the diff, no need to try and grip the crownwheel in the vice to undo it etc etc