R/C Tech Forums - Ball Diff Instructions...Want Pro's Opinion...

Introduction: Hey guys I have been wanting to write a paper on building and breaking in ball differentials and have finally gotten around to it. After reading it I welcome any feedback good or bad,your opinions, and anything you think should be added.

"How to Properly Build and Break- In a Ball Differential and Slipper Clutch"

Author: Racer53

The purpose of this article is to give instructions on how to properly build and break in a ball differential and slipper clutch for a Team Associated RC10B4, RC10T4, and SC10.These instructions will also work for any 1/10th scale ball diff or slipper clutch. I do not claim to be an expert in Rc or claim to know everything about our hobby, but there has been a great deal of confusion about this topic with all of the new racers entering 1/10th scale racing. This article is meant to clear up some of the confusion and make it an easier and more enjoyable process. There are as many different opinions on this topic as there are racers, this is just mine.

Removing the Transmission Case

To get to the diff we must first disassemble the back end of the buggy and the transmission case. Start by removing the two 4/40 size screws that hold the transmission case to the rear brace. Next remove the 4/40 size screws that hold the wing mounts to the rear shock tower, and push the wing mounts up out of the way. Now pop the rear turnbuckles off of the rear brace and let the CVD’s hand freely to the sides of the buggy. You will now need to remove the top and bottom 4/40 size screw that hold the motor guard to the transmission case. Now with a little force the transmission case will pop free. Make sure to remove the motor or unplug the leads from the E.S.C. Set the transmission case on a clean white pit towel, and push the rest of the buggy aside for now.

Disassembling the Transmission Case

Now remove the gear cover from the motor plate be unscrewing the two 4/40 size screws. If you haven’t already, you will want to remove the motor. You will now need to remove the slipper clutch assembly by removing the ¼ size nut and sliding the slipper clutch assembly, along with the spur gear off to the side. Next remove the four, long 4/40 size screws that hold the transmission case to the motor plate. Set the motor plate, wing mounts, and 4/40 size screws aside. The final screw holding the transmission together is the small 4/40 size screw on the bottom, left, corner of the transmission case. Remove this screw and split the transmission halves apart, remove the differential, and set it on your white pit towel, pushing aside the remainder of the transmission case.

The Differential

Disassembling the Diff

Now that we have the diff isolated we can disassemble it. Start by working on a clean pit towel, preferably white so that small parts will be easy to see. Insert a 5/64th size hex driver into the right side of the diff, and unscrew the thrust bolt. Separate the diff into its two halves. Clean all of the parts using motor cleaning spray or de-natured alcohol, once done organize all the parts so they are easy to find.

Next check the diff gear’s teeth for wear and chipped teeth, and replace if necessary. Now take the diff rings out of the outdrives, and feel the diff rings with your fingernail to see if there is a small ridge that the diff balls have created. If there is a small ridge, flip the diff rings over to the smooth un-used side, if both sides have been used it is time to replace the diff rings. Now take some 400 grit sandpaper and sand the diff rings in a circular pattern, until there is no shine or ridge on the diff rings. Most diff rings come too polished and cause the diff to slip because the balls have nothing to grab on to. Many diff rings also have minor imperfections, and are not completely flat. Sanding fixes both of these problems. You need only to sand the side facing the diff balls, however sanding both sides does no harm.

Building the Diff

Now it is time to build the diff. Make sure all the parts are clean and free of debris, grit, and dirt. Start by applying a small amount of Team Associated’s Diff Lube to both sides of the outdrive’s rims, where the diff rings sit. You don’t need to use much Diff Lube, just enough to cover evenly. Now set the diff rings on the outdrives. Apply Diff Lube onto the top of the diff rings, being more generous this time. Now place the diff gear onto the left outdrive[the outdrive with the nipple]. Apply more Diff Lube to the holes in the gear and place the diff balls in the holes. It is important to make sure no debris gets into the diff, so be careful. Now set the outdrives aside and we will look at the thrust bearing assembly.

If you are re-using your thrust washers check to make sure there is no ridge on the washers that the thrust balls have created. If there is flip them over to the smooth, un-used side. If both sides have been used it's time to replace the thrust washers. Now, find the diff thrust bolt and put it on the end of your 5/64th hex driver. Now slip one of the thrust washers onto the bolt, and apply a generous amount of Team Associated’s Black Grease to the top side of the washer. Next set the six thrust balls onto the top side of the washer, and apply a little more Black Grease on top of these. Slide the second washer on top of the diff balls, then slide the bolt up into the right outdrive[outdrive without nipple].

Now install the diff bearings into the diff by sliding them into the slot on the right outdrive. Apply a little more Diff Lube onto the right outdrive, and slide both outdrives together, and set aside for a moment.

Now find your diff thrust spring and t-nut. Please note that if it is a new diff thrust spring you will need to compress it first, with a pair of pliers. Slide the thrust spring into the left outdrive, followed by the t-nut. Make sure the t-nut is facing the right direction, and has the tabs on the top, not the bottom. Slowly tighten the diff, making sure the t-nut is compressing the thrust spring. Only tighten the diff enough to when you can not move the diff gear while holding both outdrives. DO NOT FULL TIGHTEN THE DIFF, AS THIS CAN CAUSE THE DIFF BALLS TO FLATTEN OUT ON ONE SIDE. Before reassembling the transmission clean out all of the old grease in the transmission gears with motor cleaner spray, and apply a couple of drops of 50wt shock oil to get a quite, smooth transmission. Now reassemble the transmission and the rear end of the buggy by reversing the steps you took in disassembly.

Setting the Diff

This next part can be confusing, so you might want to read thru it before continuing. With your car back together you can now set the diff. First, you will need to tighten your slipper clutch all the way down. Next hold the spur gear and the right wheel with your right hand and try to turn the left wheel with your left hand. You should not be able to move the wheel,[you only need to use moderate force, if it doesn’t turn don’t apply an extreme amount of force] if you can move the wheel your diff is slipping, tighten your diff about 1/16th of a turn and try again. If you can not turn the wheel loosen the diff just a little, and then tighten 1/16th of a turn when it starts to slip. You are trying to get the diff as loose as you can without it slipping, and as tight as it can without binding. After a couple of tries you should be able to find the “sweet spot”. Now that you have set your diff, we can break it in. Before you do this loosen your slipper clutch back to normal.

Breaking-In the Diff

Breaking in the diff is important and you will have a much smoother diff after this is done. To break in the diff hold one tire and give the car a small amount of throttle for about 10-15 seconds, then change sides and hold the opposite tire. Do this three or four times,increasing the throttle a little each time[Do not go higher than 1/4th throttle] then tighten the slipper and check the diff, making sure it hasn’t loosened or tightened any. You may have to tighten the diff about 1/16th of a turn as things settle in. Now loosen your slipper and do this process of 1/4th throttle, then check the diff, two to three times.

Once done put the gear cover back on the buggy and grab the left and right wheels. Slowly turn them in opposite directions, the diff should feel smooth without any binding or gritty feeling. You now have a smooth diff that is properly set up. [If any are interested I recommend running carbide diff balls and ceramic thrust balls. The reason to not use ceramic diff balls is that they are so hard and smooth; it's hard to get the diff to stop slipping.]

Setting the Slipper Clutch

I will now go over how to set the slipper clutch. To properly set the slipper clutch start by tightening the slipper nut down 3 and ½ turns from when it is flush with the bolt. Now hold both rear tires and have someone pull the throttle, give it a good pull as you are trying to simulate accelerating away from a hard landing. The front end of the vehicle should pop up about three inches. If it does not, stop and tighten the slipper nut about 1/4th of a turn and try again. If it comes up too high, loosen the slipper nut about 1/4th of a turn and try again. Every time you rebuild the diff check the slipper pads and make sure they do not have shiny spots on them, this is called glazing, and can be fixed by carefully scraping the pads with the trailing edge of an X-Acto blade or by replacing the pads. The purpose of the slipper clutch is to protect the transmission by slipping when coming down hard after a jump or accelerating hard. If a sharp whining noise is heard when accelerating, tighten the slipper nut by 1/4th of a turn and try again. Make sure you set your diff before your slipper clutch.

First Time At the Track

You just rebuilt your diff and set your slipper. Now it is time to get on the track. After rebuilding the diff and setting the slipper, you must take the first couple of laps slowly. Do not punch the car's throttle,or try and take that triple. You are trying to get all the parts in the diff settled in, so be slow and smooth on the throttle. Check the diff multiple times during the first battery pack's worth of run time. You will probably have to tighten your diff a little as it may have loosened up some as you used it. As long as you take this process patiently you will not have any problems. However if you skip this process you will have a gritty diff in no time.
Now you have a smooth diff that is broken in and a slipper clutch that is properly set up. Your diff should last quite a while, just check it every three to four runs. Rebuild the diff if it feels tight, gritty, or not as smooth as you like. The thrust balls and diff balls should last two to three rebuilds. The thrust washers, and diff rings need to be checked during each rebuild. Now the only problem you will have with your differential are people asking you to help with theirs.
Final Thoughts

Like I stated in the beginning of this article there are many different techniques and tricks to building and breaking in a differential and slipper clutch, this is just the way I do mine. This article may be shared and used be anyone, all I ask is that the author be listed as Racer53.
Good Luck,
Racer53