A spacer is a shade tree work-around to substitute for having the right ring gear carrier assembly. The most common problem with using a spacer is a rhythmic hum caused by variations in the runout of the ring gear. It's OK to run a spacer on a race car where the noise is masked by open exhaust headers, but I'd be reluctant to do it on a street-driven vehicle. Even us deaf old geezers can hear a low-pitched hum!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!