Originally Posted by LandYaghtLover

Newbie question. Do these transmission use steel or vulcanized rubber check balls? On the Ford 4-speed with OD they used rubber. Which is fine. However, standard trans fluid deteriorates them so Ford issued a TSB to use Merc V synthetic blend.

Anyway. If vulcanized, I would replace them with new since a reduction in diameter can cause all sorts of issues. Also, in my case, one was shrunk down so much it was wedged into the separator plate! Oddly, it caused no issues. Found it when doing a performance mod.