Yukon Gear Mini Spool For Ford 8.8in w/ 31 Spline Axles
If your Ford 8.8 rear end leaves one black stripe at the drag strip, spins a single tire on a rock ledge, or you are building a dirt track or pulling truck that never needs to turn on pavement, the Yukon YP MINSF8.8-31 mini spool is the cheapest way to make both rear wheels turn together all the time. It is built for the 8.8 inch Ford ring gear axle with 31-spline axle shafts, the version found under many F-150s, Explorers, Expeditions, Mustangs and Rangers once Ford moved past the earlier 28-spline shafts. It drops into the open carrier you already have, so there is no ring gear to remove and no carrier bearings to set up.
In a stock open 8.8, the two side gears and two spider gears let the inside tire turn slower than the outside tire in a corner. The same freedom lets all the torque escape to whichever tire has the least grip. A mini spool replaces those four gears with a solid steel center that engages both 31-spline axle shafts and is held in the carrier by the cross pin. The result is a locked axle: 100 percent of the torque goes to both tires at all times, the axle shafts can never turn at different speeds, and the factory open carrier and ring gear simply become a housing for a solid driveline. The YP MINSF8.8-31 is built around the 7/8 inch cross pin used in the 31-spline open carrier. Because the 8.8 is a C-clip axle, the C-clips still sit in the carrier and keep the shafts in the housing.
Before you choose a spool for a daily driver, read our open vs limited slip vs locker comparison. Yukon does not recommend mini spools for street-driven vehicles, because a locked axle hops, scrubs tires and pushes the front end in every turn on pavement. For a truck that still commutes, the 31-spline Ford 8.8 locker or a Traction-Lok clutch rebuild kit is the better fit. Yukon also recommends a full spool instead of a mini spool for vehicles with large tires or high horsepower.
The only thing that matters is the axle shaft spline count and that the carrier is an open one. With the cover off and the oil drained, remove the cross pin lock bolt and pin, push each shaft in, pull the C-clips, and slide a shaft out far enough to count the splines. Our Ford 8.8 28 vs 31 spline guide walks through the count and the shaft diameter check. If the axle is already noisy, the Ford 8.8 rear axle problems guide will help you decide whether bearings or gears need attention while it is apart.
This spool fits the Ford 8.8 inch rear axle with 31-spline axle shafts and an open differential carrier using the 7/8 inch cross pin. It does not fit 28-spline axles, the Super 8.8 with 34-spline shafts used in 2015-up F-150s and the S550 Mustang, or the reverse-rotation 8.8 front axles used under Ford IFS trucks. It will not install in a Traction-Lok carrier; that carrier must be replaced with an open case first. Ford built the 8.8 for decades in many trucks and cars, so do not order by year alone. Count your splines, look at the carrier, or send us your year and VIN and we will check it.
Drain the gear oil, remove the cover, then remove the cross pin bolt, cross pin, spider gears and side gears. Push the axles in, remove the C-clips and the original gears, then set the spool in the carrier window. Yukon notes that the factory C-clips may need a small amount of grinding so they seat properly with the spool in place. Reinstall the C-clips, pull the axles out against them, install the cross pin through the spool and torque the lock bolt with thread locker. Refill with 75W-90 or 75W-140 gear oil; friction modifier is not needed because there are no clutches. With the cover off, this is a good time to renew bearings with the Ford 8.8 master overhaul kit or lock in pinion preload with the Yukon crush sleeve eliminator.
| Brand | Yukon Gear & Axle |
| Part number | YP MINSF8.8-31 |
| Fits | Yukon Gear Mini Spool For Ford 8.8in w/ 31 Spline Axles |
| Type | Differentials |
| Condition | New |
| Ships | Same business day (in stock), from the USA |
| Warranty | 1-year |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
No. A mini spool replaces the spider and side gears in an open carrier. A Traction-Lok carrier has clutch packs and a different internal layout, so you would need an open 8.8 carrier first.
Yukon does not recommend mini spools for street-driven vehicles. Both tires are locked together, so the axle scrubs tires and pushes the front end in every turn on pavement. Use a locker or limited slip for a daily driver.
Pull an axle shaft and count the splines, or measure the splined end. The 31-spline shaft is thicker than the 28-spline shaft. The axle tag shows ratio but does not prove spline count.
No friction modifier is needed because there are no clutch plates. Standard 75W-90 or 75W-140 gear oil is fine, filled to the bottom of the fill hole with the vehicle level.
Yukon recommends a full spool for vehicles with large tires or high horsepower. The mini spool uses the factory carrier and cross pin, so it is the budget option for lighter duty full-time lockup.
