Drive shaft shim?

[JGRacing]

I did not even question this on my car until this weekend and wanted to get some opinions.  My car came with a thin shim (made from that aluminum pre-painted sheet metal used to make body panels) between the drive shaft adapter on the engine and the drive shaft yoke.  It looks like the drive shaft yoke and adapter will bolt up fine, so not sure what purpose the shim serves.  I just kept putting it back on and did not really think about it.  Does anyone use a shim like this or have any idea why it would be on my car? 

[racerrad8]

Back in the late 90's 600 changes driveshaft yokes to a heavier/larger unit. The change of the yoke also meant it had a thicker internal centering shoulder on the yoke. This thicker shoulder then bottomed out in the coupler before the actual bolt flange made contact with the coupler. This left the gap and the bolts would not tighten properly. Many driveshafts came flying out due to the bolts coming loose. The fix provided by 600 was the aluminum shim.

If the flange, at the bolts, contacts the coupler then the shim is not needed. If a gap is between the flange & the couple then keep using the shim. If you don't want to use the shim, have the shoulder on the yoke machined down to .005" shorted then the coupler recess.

Randy - RPM

[JGRacing]

Thanks for the information.  I figured that someone had a reason for making the shim, but could not figure out what it was for.  I will see if it fits tight without it.