A lot of people complain about the performance of the kits front differential. Most problems relate to the way it was built, and causes the diff to feel gritty and tight. This leads many people to spend money on the front one-way diff. I have always thought of a one-way diff as a tuning option, not a performance upgrade, but many people think that one-way diffs are always better then a stock gear or ball diff. This is not the case. I too was disappointed at the way I first built the Micro RS4's front gear diff, so I took it apart and figured out a way to make it work. Most of what I will describe will not require any special tools, but there is an optional step to break in the diff faster. First you are going to have to take your diff out, completely disassemble it and clean as much of the grease off as you can. Lets first look at the two large plastic gears (part# 73403[5]). When you removed them from the parts tree, you may have neglected to get every last bit of "sprew" off of the gears. No problem, just take your hobby or x-acto knife and carefully shave this extra plastic off. Just to be safe, it's ok if you actually put slight flat spots on the gear to make sure you get all of it off. The next step is to take the spring (part# 73403c) and stretch it so it's about 50% to 75% longer. This will help to keep the two brass gears (part# 73403a) pressed out so that they mesh correctly with the plastic gears. Believe it or not, we are done. You can reassemble the diff now. To start the reassembly, put the spring between the two brass gears and slide it into the diff case (part# 73404[1]). Line it up with the holes, and insert the steel pin (part# 73403b) to hold it all in place. Next take your plastic gears and put one on each side, but opposing ends. Then simultaneously push both plastic gears towards the centerline of the diff, and the brass gears will pull them in. Make sure they are even and equally spaced within the diff case. Squeeze a blob of grease into one of the openings, and cover the opening with a diff cover (part# 73404[6]). Flip it to the other opening and insert the two polished washers (part# Z694) on each end between the diff case and the plastic gears. Then put one more blob of grease in this opening and close it up with the remaining diff cover. Lastly, slide the purple diff tube (part# 72338) back on to keep everything together. Now you can put your outdrives (part# 73404[3]) back in. If you did everything correctly, you should notice that the diff action is much more consistent, and doesn't have any gritty spots. You may also notice that the diff may still feel a little tight. This is normal, especially in a brand new kit. You can run a few packs in the car and let the gears break themselves in. But on these cars, a battery pack can last upwards of one hour! This leads me to the optional step I mentioned at the beginning. Take a cordless drill (DeWalt, Makita) and insert the diff, with outdrives and a bearing on one end (don't put the belt pulley on). You want to insert one of the outdrives into the chuck. Use only enough pressure to grip the outdrive as too much pressure can crush it. Then hold the diff by the purple diff tube or the other outdrive and slowly run the drill. If everything is working correctly, you should see the other outdrive or the purple diff tube spinning. Start off slow, and gradually increase the speed of the drill. Then after three or four minutes, reverse the direction on the drill and repeat the same process. Note: It is not recommended that you use an A/C power drill, as these have higher rpms, and you may actually melt the diff. If all you have is a power drill, please use caution, and slower speeds. So that's pretty much it, your diff should now be a lot smoother and not as tight. Reassemble your car, and you should notice an increase in steering and turning radius.

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