Bulletproof HPI Savage X SS 4.6 - How to Shim Savage Differentials
One of the major steps I took when building this version of the BulletProof Savage was the conversion from the stock Savage X “easy access” differentials to the old school Savage Setup - a multi piece, Alloy Metal, differential which included the new Savage X SS alloy diff cups shimmed internally and externally.
The internal shims include thin shims and square shims to make the spider gears inside the diff cups mesh together better. Also, the new alloy diff cups from HPI do not flex! With the older versions of differential cups, they used plastic, which under stress would distort and compromise the mesh of all those spider gears. When that happens, they strip.
An ESSENTIAL step you MUST take if you want rock solid differentials is to shim for side to side clearance. This is BEST done with the alloy diff CASES as opposed to the plastic diff cases because the alloy cases don’t flex, don’t wear at the bearing races, and are generally more ridgid.
To shim the savage differentials, you need to get the hpi hellfire shims, which will take out the clearance between the crown gear and the pinion gear. You want them to mesh to where they are tight, but not crushing up against each other. One shim on the crown gear side and one on the cup side is what worked for me with the GPM diff cases. For you, it may turn out different…but that’s a start!
Here are some pics installed…to reduce weight, you may want to go with the diff cases only, using the plastic bulkheads. I got the gpm bulkheads for the bling factor (and I don’t think the bulks are vulnerable to bending).
Notice the thick piece of foam I have down in there between the bumper and the diff…this acts as a bumper for those hard landings when I happen to land on either end:
Here’s another shot of the savage differential, shimmed and installed:
