Not a problem. I'm kind of fanatical about my race builds, and I tend to do the same things on my restos (as if I really knew what I was doing in 1990).
- Every hinge pin is polished with a Dremel and Nev-R-Dull polishing wadding or Blue Magic metal polish. If the hinge pins are chrome finished like the Team car's pins are, I just dust the ends on them on a bench grinder with a buffing wheel to take the burrs off of the e-clip slot.
- On all suspension parts with .125" hinge pins, every nylon hole is chased with a .125-.126" straight fluted hand reamer chucked in a cordless drill on a low speed. My goal is that the pins slide in and out of the arms and c-hubs as if they were lubed up. You can buy straight fluted hand reamers at McMaster-Carr for almost nothing. I own a few in different sizes for different cars (like metric 3mm pins or smaller Losi hinge pins). I generally prefer to oversize .001-.002" for bets fit in nylon parts. Less oversized in molded graphite or metal parts.
- I want ZERO bind between any parts. I use a fine grit polishing emery board (found in the beauty supply section at Target or Wallmart) to make sure that the suspension pieces fit nicely together. Not too loose, but there should be little or no friction between them.
- Clean off all mold flashing and edge flashing on any nylon parts with an X-acto knife. From my model building days—I just can't leave burrs or sharp edges on anything.
I always keep a good supply of motor shims, plastic washers, #4 aluminum washers and other odd shims to take any extra play out of pins or suspension parts. It's the race builder in me, I guess. Even with a resto, I want it to be built as if it were racing this weekend at a National event.
The diffs are built like I would build my race diffs in a touring car or dirt oval car. I have a pretty simple build process that results in perfect diffs every time.
1] Wash hands. Keep everything clean. Work on a clean paper towel. Have in front of you: 400 and 600 grit wet/dry 3M sandpaper, paper towels, a glass plate, WD40 and motor spray or electric contact cleaner, plus the Associated black grease and your favorite diff lube.
2] Fresh diff balls and thrust balls are always best whenever rebuilding a diff. They make the difference between lumpy and smooth diffs. In my race rides, I use carbide or even high grade ceramics. In restos, a fresh set of chrome steelies are fine.
3] Ring sanding: stock rings are all stamped on a press and therefore are anything but flat. I take the backside of a ring in the female side of a diff, and with a little WD40 on the 400 grit paper, then place everything on the glass plate and sand the rings in circles, for at least 3 minutes per side. I use the "back" of the stamped ring in the diff, so this is the most crucial side to flatten out.
Do both rings, evenly. After you finish with the 400 grit, spray the 600 grit and with the diff half, sand the back side of the ring in "figure 8s" lapping the diff ring smooth. Do both backs of both rings, then spray with motor spray and dry with a clean paper towel. This is imperative that the rings are flat, smooth and clean. 600 grit is all you need, as the size of these balls won't feel anything any finer, so it's a waste of effort on a diff ring.
4] I also sand the thrust assembly rings on my fingertip on the 600 grit for a few seconds on each. Make sure to clean everything and dry it all when you're done.
5] Assemble the thrust assembly using the Associated black grease ONLY! Don't ever use anything else on your thrust bearings. It's been the best for almost 20 years, and I use nothing else on any car. Pack the assembly with grease like a car wheel bearing and wipe off any excess before installing into the diff. You shouldn't have any grease on the outside of the assembly. Again, it just makes a mess and attracts dirt.
6) Assemble the diff by taking some diff lube on the tip of your index finger and giving a little scrape to the naked diff half. It's all you need to keep the ring from slipping around. CA is not needed here. Apply the rings to the diff, with the freshly sanded "backs" towards the center gear. I use my finger tip to put a nice, think coat of diff lube on both of the rings, and that's all. My personall favorite diff lube is the old school VRP fluorescent pink stuff, but the Associated Stealth lube also works well. You don't need a lot of lube at all—all it's there for is to keep the balls cool, not to be slippery. More than a film just creates drag, attracts dirt and grime, and makes a mess.
7] If the diff cases bind, I like to use brass .010" motor washers between the case halves to loosen up the inner parts in the diff. Everything stays clean inside, it's just not all bound up by tight molded nylon case halves. I do this on ALL of my oval gearboxes.
8] After the tranny is built and assembled, there is one last major part of the build, and that's the break-in. If it's a shelf car, none of this matters much at all, but picking up a car and spinning a buttery smooth diff is always a buzz for me, so I do it to any diff I build.
With motor and electronics in the car, and a fully charged battery, turn on your radio and car, and hold the car off of the work surface by ONE rear tire. While holding the one tire with the other rear firmly on the surface, run the car at 1/4 throttle for 30 second, then to 1/2 throttle for another 30 seconds. Do the exact same thing to the other rear tire, then repeat the process one more time. Your diff is now fully broken in and should be cocoa butter smooth.
Fanatical? Hell yeah. But I enjoy the build process more than anything with R/C cars, so it's what I do. My cars are all race-ready and built as perfect as I can make them, and it's not just about how they look. They all could be raced right now if I wanted to.
