IRS carrier bearing preload

[scv6]

Hi. I am wishing to rebuild my diff. I intend to change the gears, add and lsd centre, which I plan on tightening.
But im having trouble finding any specs for the bw78.
How do you set carrier preload?
Ive built a few live axle diffs before and I have set carrier preload by feel. i.e. the center needs gentle encouragement with a soft mallet to install. (hey might sound rough but its worked for me and lasted the kms)
If anyones rebuilt one before Im keen to hear from ya.
or if ya got any input, let me know.
cheers.

[Not_An_Abba_Fan]

This is taken from another forum but it works on all diffs as far as I am aware.

Yes there is an easy way to tell if you have the proper preload on the side bearings. Here is the formula.

Total preload (in/lbs. with the unit totally assembled) minus the pinion bearing preload (with only the pinion assembly) multiplied by the gear ratio = side bearing preload.

If your total preload is 32 in/lbs - pinion preload of 25 in/lbs = 7 in/lbs x ratio of 3.73 = 26.11 in/lbs side bearing preload.

And this is the procedure:

1. Remove cover - allow oil to drain.
2. Clean teeth with solvent, check tooth contact pattern, and record.
3. Check backlash in 3 spots around ring gear (general specification is .005" to .009" with no more than .002" variation).
4. Check ring gear runout (.003" maximum).
5. Remove axles.
6. Check total preload and record.
7. Mark and remove side bearing caps.
8. Measure shims on both sides and record.
9. Check pinion bearing preload and record.
10. Inspect all bearings, races, and gears for pitting or other damage.
11. Replace pinion bearing races (if required).
12. Check pinion depth with special tool (if available).
13. Replace pinion bearings with correct pinion depth shim in place (lube bearings lightly).
14. Install pinion gear, new crush sleeve, front bearing, seal, yoke, washer and nut.
15. Tighten pinion nut until proper pinion bearing preload is achieved and record (should be 15-20 lbs./in. for used bearings and 20-30 lbs./in. for new bearings).
16. Replace side bearings and races (lube lightly).
17. Hold ring gear and differential case assembly in place.
18. Temporarily place a waved shim (.040") on outside of right side bearing race.
19. Pack left side bearing with shims until zero backlash is obtained.
20. Pack right side bearing to zero preload (remove waved .040" shim).
21. To set backlash and side bearing preload subtract .004" from left shim pack and add .012" to the right shim pack
22. Install side bearing caps and torque bolts to specifications.
23. Check backlash in 3 places and record (should be .005" to .009" with less than .002" variance).
24. Check total preload and record.
25. Use the following formula to check side bearing preload. Total preload - pinion preload = _______ x axle ratio = side bearing preload.
26. Side bearing preload should be 15-30 lbs./in. for new bearings.
27. Use gear marking compound and check the gear tooth contact pattern to double check setup.
28. If backlash and side bearing preload is within specifications, finish assembling the remaining parts, torque all fasteners to specifications.
29. Add the correct lubricant and road test vehicle to confirm the repair.

[scv6]

Thanks for taking the time to give such great reply. I run some quick numbers with a known diff specs and it looks to be on the money.
I was taught (rule of thumb) that it should be about double pinion preload with crown wheel meshed, but ive found that not to be correct in sum applications.
Anyways, thanks again. Appreciated.