Personally, if you want a ratchet style locking differential , especially for a Ford 8 or 9 inch, I would scrape up the extra money and buy a real Detroit Locker. All these cheapy lockers that fit inside the existing diff case, put all the power thru a pin that was originally designed to mount the spider gears. Where a real Detroit Locker has its own case, and the locking mechanism is mounted inside, and transfers the power thru a series of splines located all the way around the locking unit and inside the case. Much stronger. And due to the 9" (and 8" as well), having the rear pinion support bearing, the design requires a severely stepped down diff case to clear that bearing, which precludes using clutch packs on both sides, like virtually any other clutch type limited slip unit employes. As well, since it appears that the 9" was designed without a limited slip in mind, when Ford did decide to make their own clutch style limited slip unit, not only were they restricted to having clutch plates on only one side, they could only carve away enough material inside the case and side cover to allow a few clutch plates, typically less than 1/2 of what a GM, MoPar, or even a Ford Traction Lok for a 8.8 contains. Which plays a big factor in why it is so common to see a 9" Traction Lok either spinning only 1 tire, due to minimal clutch surface and preload, and if the spring pressure is increased, or driven hard, the side cover split around the ring gear bolts, where the case and cover have been cut away to fit the few clutches in that they could squeeze in there.