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Pinion Preload
Now comes some of the fun stuff, setting the pinion preload.
"What is preload and why is it needed?" you might ask.
There must be sufficient pressure on the pinion bearings for proper operation. If they are too loose, you may hear some bad noises from your diff, maybe a low howl at low speed, and whine at higher speeds. This is the sound of your pinion bearings self-destructing because they are not being held in place well enough. If they are too tight their lifespan will likewise be significantly shortened.
Getting the preload wrong is why I did this job twice - complete assembly into the car, immediately followed by complete removal and disassembly and starting over. Better to miss the first autocross of the season than make it and blow up the (expensive) diff and gears.
This is where the inch lb torque wrench will be used BTW.
Read the FSM instructions. Then read them again.
Keep reading them until you know them by heart and can recite them from memory. Seriously, this is one place you don't want to screw up.
The diff will need to be very securely mounted, as you will be putting a lot of torque on the pinion nut.
There isn't too much I can add in addition to the FSM instructions.
Here is the little I can add.
Once the collar begins to crush, you will know it, as the pinion nut gets very hard to turn. I don't think I can overemphasize this point: Tighten in small increments, remove the brace frequently, and check the pinion preload.
When you check the preload, be sure to spin the pinion a few times to relieve any binding. It will be quite bound up after you take the wrench off the nut and brace off the flange. I put a little lubricant on the bearing, then put a drill on the pinion for 2-3 seconds to made sure it was loosened up. If you don't relieve the binding the preload measurements will be way off.
The FSM instructs you to assemble everything except the front pinion seal, set the preload, and then record the ft lbs of torque required to get the preload correct ( 12-15 inch lbs). Following that you disassemble, install the oil seal and re-assemble, torquing the nut down to the recorded value. In addition, I torqued the nut down in increments, making sure the preload didn't exceed the specified value. The torque required for mine was 166 ft lbs, and it came out correct at reassembly.
When measuring the preload, measure it while the pinion is turning, as more torque is required to start the pinion turning than is required to sustain the motion.
Be sure not to forget the spacer on the crush collar, and the washer under the nut.
The attached pics show the inch lb torque wrench being used to check the preload, and a bearing race being used to seat the front pinion oil seal.
Next: Differential bearings
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