tranny overdrie on 2000 Pontiac Montana

my 2000 montana has 140000 mi. on it
transmission works good just no overdrive, what could be the problem

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1 answer
i work at a tranny shop and fixed this problem a few times. the overdrive drum has a short shaft at the end of it with very fine splines. after a while the splines wear out and strip, causing the drum not to spin. the tranny wont blow up, but i recomend getting it fixed asap because of the fine metal shavings in the tranny.