Diff drag is the amount of torque that it takes to turn the differential pinion gear. With the diff and rear axle fully assembled and on the car, it is measured with the axles as level as possible and no resistance by brakes on the rotors. The manual gives a spec of 22-26 in/lbs on a new rear axles assembly. To get the axles level, jack stands are placed under the axle tubes as close to the wheels as possible and weight is placed in the trunk to overcome the compensation spring. The driveshaft is then removed from the diff yoke and moved out of the way. To accurately measure the diff drag I used an in/lb dial guage that I found online. It is basically a type of torque wrench that shows you on a dial the amount of torque being applied, rather than a standard torque wrench that clicks or "breaks" when the specified torque is reached. Several companies make them, some are very expensive. I attached the dial guage to the pin wrench socket that is supposed to fit the diff pinion nut for our cars. This pin socket is the M0030 from SIr Tools, but I still had to modify it because the pins were too long and did not allow the socket to fully seat itself completely. My rebuilt 3.27 with a new pinion seal but original bearings measured about 12 in/lbs.
and I had a distinct whine with this setting.
I then used the procedure outlined at that website:
http://www.bernardembden.com/xjs/diff/index.htmI also used my dial guage to measure what I was doing, but my goal was not to achieve factory spec. I only used the guage to see if I was really increasing my diff drag with a 1/8" turn of the nut. My plan was to make a 1/8" turn of the pinion nut, put everything back together and drive the car and see if the whine was gone. If it wasn't, I would have to do it all again and then drive it again. Fortunately, the whine disappeared with just one 1/8'' tightening of the nut. This is the safest way to go because you do not want to overtighten the nut. As it turned out, the diff drag ended up at 16 in/lbs: still under factory spec, but this is not unexpected for a used differential. My purpose was to get rid of the whine and not necessarily to acheive factory spec. I'm sure that if I tried to get to factory spec that I would have overtightened it.
Tightening the pinion nut with the yoke fixed is very difficult. It takes tremenous force and the pin socket wants to slip off the nut. I was able to do this by holding the wrench-socket onto the nut with a C-clamp hooked on the back of the diff, and a used a bottle jack to turn the wrench handle in small increments.
I do not know what your "clunk" is. My diff did not have this. I think that you are assuming that the clunk is a result of too much backlash. In other words, there is too much play of each pinion tooth between two crown teeth. However, the clunk may be the result of something else, maybe a bad bearing?
