Post Tue Dec 19, 2017 2:05 pm

Re: Ramblings on building differntials

I don't recommend pre load on wheel bearing and I don't recommend a torque wrench reading. With wheel bearings when you tighten the outer nut, it will increase the load you set with the torque wrench.
On my heavy truck wheel bearings I find they have to loose (a few thousandth of play) to get to zero when you tighten the outer nut. I find it takes a few tries at tightening the outer nut to get where I want to be. I have to take the outer nut and lock washer back off, and loosen or tighten the inner nut one "index" on the lock washer, then re torque the outer until I have as near zero play as possible.
You should always tighten the inner down with the wheel rotating, to be sure the bearing is seated and not "cocked" on the shaft. Then loosen the inner nut to just a bit of play and see how it locks down, then make adjustments as described above.
Diff bearing preload will be called out in the overhaul instructions, but is useallly in the 28-32 in/lb range. There are many ways to test this, a string and spring scale is the cheapest, a threaded rod passed thru the carrier and heavy washers on the end, tightened down so you can use a dial- type in/lb torque wrench would be on the elaborate side of thing, and not cheap. it has to be a dial type torque wrench and not a beam or click type, because you have to read the torque to keep it turning, not the torque it took to get it turning. Some books call for measuring how much the case spreads under pre-load, you take a dial indicator clamped to one bearing cap and measure to the other, and spread the caps by .001"
When I did my first rear, I was at a dealership with all the special tooling. The best "tool" I had was an older gray-haired mechanic who took a liking to me, I could explain the "newfangled" electronic's like voltage regulators and ignition to him, and he gave me tons of good tips. After I had set up the pre-load with the tools, had the back lash set and tooth contact, he came over and grabbed the ring gear and moved it back and forth, He said "kid, feel this, and memorize what it feels like, then put those tools back in the cabinet for the next rookie, you'll not need them again!" You want a little drag, on a heavy truck diff, with adjuster nuts, it is most often one to two notches from 0 preload. It is hard to explain the "feel" but if you do one or two with a measuring device, be it a spring a spring scale or a torque wrench, you should be able to memorize the "feel".
If you are just re-bearing the diff, just put the same bearing spacer (pinion) and mark the bearing adjuster nuts location and re-set to where it was. DO NOT mix adjuster nuts from side to side, ALWAYS put it back where it came out of. A few paint sticks in different colors can be a help. They can mark which tooth (lug on the nut) lined up with the lock or cotter pin (some use a L shaped lock, others use a large cotter pin to lock the nut to the cap).