Originally Posted by
zaraz
what is the trick to build the rear diff, I have tried toothpaste, rubbing compound, etc etc, the gear diff is not smooth, you can still feel the meshing, with the 417x, the diff was smooth as butter, does getting the xceed gears help with smoothness, i know they are lighter, but are they smoother, thanks
I ended up using a medium valve lapping compound, its pretty gritty though. I took out the seals, and put the diff together with the compound in it, then I put it in a drill press, on low speed, and locked the frre end of the diff up and let it spin for about 3-4 minutes, then turned it over and spun it the other way for the same amount of time. Clean everything up, this is important as the lapping compound is very tough to get cleaned. Now put the diff back together, but I leave out the big washer that goes between the big gear and the o-ring. I use a little bit of green slime on the o-ring and the output shafts and fill the diff with LOSI 90wt oil to the cross shaft pin. I green slime the outer o-ring on the housing and button it all up. The diff is very smooth now, and will spin a couple of rotations if you spin the opposite wheel, like a looser ball diff. So far I have no leaks and it works very well.
A couple of things to take note. The shim washers, the big ones and the little ones when you do the lapping compound break in will actually show the high and low spots of the big and small gears. With that you could possibly get a smooth diff by sanding the backs of the gears, but you will still need to do a slight break in of the gear teeth. If you do the lapping compound you should probably polish the small washers after you break it in, like you would for a ball diff, and polish the cross shaft pin. The small washers are used to set the backlash of the gears, but I don't feel that running without the big shim between the gear and o-ring is a problem, if I could get a washer half as thick I might try that.
I can't stress how abrasive the lapping compound is, so the less time on the drill press the better. The problem is that it could create slop in the bushing part of the gear cases. If I where to do another breakin I would use some cheap o-rings in the cases between the gear and housing just to make sure that none of the compound weeps into that area. Better to be save.