[andrew]

Hi guys im in the process of changing the pinion seal in the rear diff
To tidy up oil leaks before 1st rego.
Ive noticed going from reverse into 1st there is a clunk when i start moving which i figure is back lash in the diff, anyways when i un did the nut it was flush with the spline and didnt seem as tight as i thought it would be. Does any one know how many threads are supposed to be sticking through the nut for correct preload on the pinion?

Thanks

[jdk81]

You need a new crush tube in there so you can set the pinion preload correctly, as per factory service manual.

To set the backlash, you need to pull the complete 3rd member out and adjust it correctly, as per factory service manual.

[andrew]

Yeah ive got the factory service manual didn't say anying about a crush ring or how far to screw the nut onto thr spline. Ill have to have another read through of it

[watermouse]

Preload on the pinion is set with the center removed. It is measured as a certain torque to twist the pinion, not thread counts. It can also be done with a spring balance and string to measure this torque.
It is done this way because once you have the centre back in and the pinion and ring gear are engaged the side bearing position and preloads are set which affects the apparent pinion preload.

You will not be able to set the correct pinion preload without disassembling the diff and starting from scratch with a new crush tube. Setting pinion preload will not affect backlash unless the pinion was already sloppy loose. Backlash can only be adjusted by adjusting the centre and ring gear across closer to the pinion.
In my experience from trying to do this (resulting in a diff that chewed itself out) and from professional advice, backlash adjustment on old diffs should be avoided if you expect longevity. A diff with mega backlash is almost certainly ready to fail from excessive wear anyway.

Your best solution it to tighten the nut back to the same position as it was before, if you kept a note of where that was by thread count. The probable reason it was looser that expected is from pinion bearing wear.