For those that know me and my racing habits, you can easily tell I like to keep my race cars in tip top shape. After every race day I go through the car and clean it. I take most of the car apart and do what I call the “weekly maintenance” to it. After all, these are race cars and if you neglect and overlook these little land rockets you will find yourself scratching your head on race day saying “something on my car doesn’t feel right”. So in order to get you’re car to perform to it’s maximum ability you must stay on top off diff maintenance! I actually rebuild my diff after single race day. I’m not saying you have to go to that extent, but try not to let it go more than 3 races. I race just about every single weekend and I have been on that pace for that last 3 years or so. Do the math……yup, I have built (a lot) of diffs over the years so I have learned through time what to do and what not to do to achieve an absolute winning diff!
Step #1: Make sure you’re work bench is covered with a clean pit towel and try to work under a desk lamp so you have good light to work under. Take the diff apart and clean all components. My favorite solvent to use is just your typical motor cleaner. Don’t use the motor cleaner on the thrust bearing, just wipe off it with a clean rag. Go through all diff parts and get rid off any diff grease and dirt that it has gathered from the race track. As you can see, I’m soaking the diff balls in the motor cleaner while I work on other parts of the diff. Let them sit for at least 5 minutes. The best diff balls you can get are by far Acer Ceramics! They are ultra smooth and last a good quarter of a race season. You will not be able to get your diff on the next level unless you have them.
Step #2: You have to clean the inside diameter of the pulley where the balls sit and make their home. I take a rag and dip it in my motor cleaner bowl then pinch it tight so it’s able to slip and pull through the other side. Take it and go back and forth a few times. Do this to all the holes in the pulley.
Step #3: Take the diff balls that have been marinating and wipe then dry one by one. Place them down on your pit towel in a nice, safe place.
Step #4: This step is the most crucial. Sanding the diff rings makes all the difference in the world. The absolute best procedure to go about this is to start off with 600 grit sand paper. Do this on a hard, flat solid surface. Go in a up and down motion, press down somewhat hard and move your hand fast. Sanding in circles doesn’t work. Give the rings a nice consistent pattern by going up and down throughout the whole procedure. Don’t sit there and sand slow and lazy. If your arm starts getting sore, you are doing it correctly! Sand both sides of the ring for max performance and a smoother diff! Now go to a less gritty sand paper in the range of 1000-1200 grit. Proceed with the same routine. After this you should notice the rings almost develop a nice shine to them. Don’t rush through this. It’s a 5 to 10 minute step. When you are done sanding the rings, simply take a rag and wipe them clean by using the same technique you used to sand them. Place rag on solid surface and motion up and down with the ring to add a wonderful shine. Don’t use a polish/waxer to shine up diff rings! Only the rag technique. The polish adds a film to it and makes it too shiny and slippery so the diff balls have a hard time grabbing the surface.
Step #5: Now we start assembly. I’ve been using AE Stealth diff lube for the last few years. It seems to be the most neutral and consistent lube out there. I’ve tried others, but always end up using Stealth. The other lubes out there just don’t feel right to me. Place a little dab of grease in each whole of the pulley where the balls will be placed.
Step #6: Apply diff lube to rings. *Don’t put too much lube on rings, it’s not nescessary. If you build a diff, go out and hit the track and you notice after the first run that lube has spit out around your pulley and collected dust……you put too much on.
Step #7: Proceed with the rest of the diff assembly. Most diff adjustments are fairly similar to each other. Screw diff adjustment down until it completely stops and hits bottom. Double check because sometimes it might fool you into thinking your at the bottom but need to give it an extra half turn until it fully stops. Typically at this point back off the screw a quarter to a half of a turn. Lately, I’ve been doing mine a good half of turn. At this point, feel the diff. Motion the outdrives back and forth in your hand. It should feel ultra smooth. If you feel a slight wave or hump as you motion the assembly that usually means the rings were not sanded enough.
The actual diff adjustment is vital to the set-up of the entire car and to the way it performs. I often see many racers with an over tightened diff. This will make the car loose feeling and touchy on power. Pay close attention to your car coming off the starting line and also how it comes out of the corners. That’s when the diff is working it’s hardest. If you have built your diff with my procedure you should notice more snap coming off the holeshot and more burst as you get on power to carve the infield.
*Other tips to note*
Stay on top of the ball thrust bearing. Once they get worn out, your diff will never be right. A good rule of thumb is to replace the thrust bearing every 2 months.
You should be able to use the diff rings multiple times by using the sanding technique I described. Sometimes I find they get better through each build!
