Shimming differentials

[ohmygahitscoby]

Hey guys,

How will I know if my differential is perfectly shimmed? Is there a specific number of shims to put on each shaft? Please help me, thanks!

It's for a Savage25 with Aluminum differential cups and spider gear mods.

-Coby

 

[Scrogg]

You want the ring and pinion to be set as tight as possible but still spin smoothly. If it has one slight rough spot in it, don't sweat it. That is better than being too loose.
Use just enough shims to remove all the side to side play of the whole diff assembly. If you use tooo many shims it will side load the bearings and cause them to fail.
There is a nice sticky on savage-central on diff building.

 

[olds97_lss]

There is a nice sticky on savage-central on diff building.

Talking about this one I copied a long time ago?

https://www.rcnitrotalk.com/forum/showthread.php?t=47876&highlight=shim

 

[ohmygahitscoby]

Awesome, thanks! Just wondering, but should I shim the little bevel gears inside the differential cup?

 

[olds97_lss]

I didn't have any need when I did it. The gear lash inside the cup is pretty fixed, so you shouldn't have to worry about it.

I would suggest though upgrading to the new alloy HPI cups. I bought two XL diffs off ebay not too long ago and they are built a lot better than the older diffs. The cups are alloy and the main ring/pinion gears look to be milled vs cast.

The only downside the the XL diffs is that the outdrive cups are too big to fit many alloy aftermarket diff cases. I bought Hot Racing diff cases to help prolong the life of my diffs (due to less case flex) and the stupid cups were too big. So, I had to tear down my old diffs and re-use the cups/shafts from those. Everything sure fit nice and pretty after that. Nothings better than a well built/shimmed diff!