Yukon Ford 9" Steel Full Spool – 40 Spline
YUKYP FSF9-40
The Yukon Ford 9" Steel Full Spool provides permanent axle lockup for dedicated off-road, rock crawling, mud racing, drag racing, and competition vehicles. Unlike a conventional differential or automatic locker, a full spool mechanically connects both axle shafts so equal torque is delivered to both wheels at all times.
Manufactured from heat-treated 8620 steel, this spool is built to handle the shock loads created by high horsepower, aggressive launches, oversized tires, and severe off-road use. Designed specifically for Ford 9" differentials using 40-spline axle shafts, it replaces the factory differential carrier with a simple, durable traction solution for vehicles where maximum strength and consistent wheel speed are more important than street-driving manners.
Includes:
- (1) Yukon Ford 9" Steel Full Spool
Note: Designed for 40-spline axle shafts. Not recommended for street-driven vehicles.
Specifications
| Specification | Details |
|---|---|
| Manufacturer | Yukon Gear & Axle |
| Part Number | YP FSF9-40 |
| Product Type | Full Differential Spool |
| Differential Application | Ford 9" |
| Spline Count | 40 Spline |
| Material | 8620 Heat-Treated Steel |
| Traction Type | Permanent 100% Axle Lockup |
| Carrier Replacement | Yes |
| Recommended Use | Racing and Dedicated Off-Road Applications |
| Street Use | Not Recommended |
| Quantity | Sold Individually |
Fitment
| Make | Model | Year Range | Differential |
|---|---|---|---|
| Ford | Bronco | 1966–1986 | Ford 9" |
| Ford | E-100 / E-150 / E-200 / E-250 Econoline | 1969–1980 | Ford 9" |
| Ford | F-100 / F-150 | 1957–1987 | Ford 9" |
| Ford | Fairlane | 1957–1970 | Ford 9" |
| Ford | Falcon | 1960–1970 | Ford 9" |
| Ford | Galaxie / Galaxie 500 | 1959–1974 | Ford 9" |
| Ford | Gran Torino | 1972–1976 | Ford 9" |
| Ford | Granada | 1975–1979 | Ford 9" |
| Ford | LTD | 1965–1979 | Ford 9" |
| Ford | Maverick | 1970–1977 | Ford 9" |
| Ford | Mustang | 1965–1973 | Ford 9" |
| Ford | Ranchero | 1957–1979 | Ford 9" |
| Ford | Thunderbird | 1955–1979 | Ford 9" |
| Lincoln | Continental | 1958–1979 | Ford 9" |
| Lincoln | Mark III | 1968–1971 | Ford 9" |
| Mercury | Comet | 1964–1977 | Ford 9" |
| Mercury | Cougar | 1967–1979 | Ford 9" |
| Mercury | Grand Marquis | 1975–1980 | Ford 9" |
Fitment Notes:
- Fits Ford 9" differentials configured for 40-spline axle shafts.
- Replaces the differential carrier assembly.
- Compatible with many aftermarket Ford 9" third members.
- Vehicle fitment alone does not confirm compatibility; the axle must be equipped with a Ford 9" differential and 40-spline shafts.
- Verify spline count, carrier configuration, bearing requirements, and third-member setup before ordering.
- Professional differential setup is recommended.
FAQ
What is a full spool?
A full spool replaces the differential carrier and permanently connects both axle shafts. This eliminates differential action and sends equal torque to both wheels at all times.
Is a full spool stronger than a locker?
A spool contains no internal locking mechanisms or moving differential components, making it a simple and highly durable option for extreme racing and off-road applications.
Can this spool be used on the street?
Street use is not recommended. Because both rear wheels remain locked together, the tires must scrub during turns, which increases tire wear and negatively affects handling on pavement.
What axle shafts are required?
This spool is designed specifically for Ford 9" differentials using 40-spline axle shafts. It will not fit lower-spline-count axle shafts.
Is a spool a good choice for rock crawling?
Yes, for dedicated off-road builds. A spool provides constant traction and eliminates the possibility of a locker disengaging or failing under load. It is commonly used in competition crawlers, rock bouncers, mud trucks, and drag racing vehicles.
Does a spool affect turning?
Yes. Since both axle shafts rotate at the same speed, the inside tire cannot slow down during a turn. This causes tire scrub and increases stress on axle shafts, tires, and other drivetrain components when operating on high-traction surfaces.
