Detroit locker offered as OE in some Ford Dana 80 rear axles.
1 Case Assy.
2 Thrust Washer
3 Side Gear
4 Preload Dampener Kit
5 Spring Retainer
6 Spring
7 Clutch Assy.
8 Central Driver Assy.
9 Case Bolt (8 Req'd.)
The locking differential differs from the limited slip differential in that the latter is torque sensitive. The locking differential, however, is speed sensitive but not torque sensitive. The limited slip differential accomplishes its function of torque transfer via a set of friction plates. The amount of torque that is transferred varies with the type of slip condition (torque sensitive), and the speed of the slipping wheel will not increase the torque once it has reached its maximum. The Detroit Locker® locking differential accomplishes torque transfer via the central locking system that transfers 50 percent of the torque to both wheels as though no differential existed and the axle shafts were joined together. But the Detroit Locker® is speed sensitive in that, when cornering, the outer wheel must travel faster than ring gear speed, which will cause that wheel to disengage or cam out from the central driver inside the differential case (4204). When the turn is completed, the outer wheel slows back down to ring gear speed and a preloaded spring pushes the outer wheel clutch back into the lock position. When the outer wheel is disengaged, 100 percent of the available torque goes to the inner wheel. The 50 percent torque transfer and 100 percent torque transfer when turning are known as non-torque biasing, and greatly increase the vehicle's ability to climb out of deep mud, dirt, sand or snow.
The teeth on the central driver assembly and the right and left wheel clutches are dovetailed at a five-degree negative angle so that when they mesh, they cannot inadvertently cam out. When the vehicle is traveling straight, the teeth push more tightly together. Without the dovetail cut of the meshing teeth, the clutches would cam out causing the wheels to disengage from the central driver. Instead, the dovetail cut allows the teeth to mesh together as tightly as possible without the clutches camming out.
As long as the vehicle is operated in a straight forward or reverse direction over a smooth surface, the driven clutch assemblies remain locked to the central driver assembly. The Detroit Locker® differential allows the vehicle to perform as if the axle halfshafts had been welded -- the axle is completely locked. This means both wheels turn at the same speed. If one wheel loses traction or leaves the ground, the opposite wheel, which still has traction, continues to drive the vehicle until traction is regained by both wheels. There can be no one-wheel spinout.
When the vehicle turns a corner, or when one wheel passes over an obstruction, the outside wheel, or the wheel passing over the obstruction, must travel a greater distance and therefore faster than the other wheel. When this occurs, the Detroit Locker® differential automatically allows for the necessary difference in wheel speed.
During a turn, the inside driven clutch remains completely engaged with the central driver and continues to drive the vehicle. The outside driven clutch automatically disengages from the central driver, allowing the outer wheel to rotate at ground speed in the turn. When the vehicle completes the turn, the outside driven clutch automatically re-engages the central driver, and both wheels again travel at the same speed.
The Detroit Locker® differential powers both wheels yet freely permits wheel speed differentiation when required.
Prime Functions
1. Assures 100 percent of the available torque and increases drawbar pull.
2. Prevents wheel spin and power loss when one wheel loses traction.
3. Compensates for differences in wheel travel when turning or operating on uneven surfaces.
Note that there are no spider gears, but rather two drive members called driven clutch assemblies. They mate with a central driver assembly, which is driven by the ring gear through the differential case assembly.
Operation in Forward or Reverse
When a Detroit Locker® differential-equipped vehicle is operated in straight forward or reverse direction, over smooth terrain, the central driver assembly and driven clutch assemblies remain fully engaged. The Detroit Locker® differential operates as a locked unit; both wheels are driven at ring gear speed and in ring gear direction.
Operation in Turns
When making a turn, differential action is required to permit the outside wheel to travel a greater distance, and faster than the inside wheel. Therefore, the Detroit Locker® differential allows the outside wheel to turn faster than the ring gear speed, but does not permit either wheel to turn slower than the ring gear when engine power is applied.
When negotiating a right turn, for example, the right driven clutch of the Detroit Locker® differential remains fully engaged with the central driver. The central driver transmits power to the right driven clutch, which drives the right (inside) wheel at ring gear speed. The left (outside) wheel covers a greater arc than the right (inside) wheel, and, driven by the traction of the road, turns faster than ring gear speed. Likewise, the left driven clutch turns faster than the central driver. The springs act as return devices for the driven clutches when their speeds are again equal.
The teeth on the right side of the center cam mesh securely with the teeth on the right driven clutch. With the center cam locked in this position (so that it cannot rotate with respect to the central driver), the cams on the left side of the center cam serve as ramps upon which the mating teeth on the left driven clutch can rise, enabling that driven clutch to disengage from the central driver.
After the left driven clutch assembly rotates forward, the slot in the left holdout ring contacts the central driver key, and positions its lugs ahead of the slots in the center cam. This prevents the left driven clutch from re-engaging with the central driver as it rotates faster than ring gear speed. When this overrunning action ceases and the relative speed of the central driver and overrunning clutch become the same, the left holdout ring lugs re-engage the center cam slots, permitting the left driven clutch to return to full engagement with the central driver.
When negotiating a left turn, this procedure is reversed. However, the operating principle is identical.
Central Driver Assembly
This assembly consists of the central driver, center cam and snap ring. The central driver has splined teeth on its outer circumference. These splines mate with internal teeth on the inner circumference of the flanged case half. The central driver has teeth that mate with teeth on the driven clutches. These teeth transmit torque from the ring gear to the axle shafts and wheels. The center cam is mounted inside the central driver. The center cam is held in position by a centrally mounted snap ring which permits the center cam to rotate within the central driver.
The center cam, which is symmetrical, has the same number of lifts as there are driving teeth on the central driver. These lifts have low-friction ramps for disengaging the driven clutches.
The center cam has slots at the outer circumference -- one narrow slot to mate with the long-tooth key and three wider slots to mate with lugs protruding axially inward from the holdout ring.
The central driver has one key (longer tooth) protruding radially inward from its inner diameter to restrict the rotation of the center cam and holdout rings.
Driven Clutch Assembly
This assembly consists of a driven clutch and holdout ring. Two identical driven clutch assemblies are located on each side of the central driver assembly.
Each driven clutch has radial teeth that mate with teeth on the central driver. The inner driven clutch teeth mesh with the cams of the center cam. The internal diameter of each driven clutch has splines which engage the external splines of the side gears.
When assembling the two driven clutch assemblies to the central driver assembly, the slot in each holdout ring must mesh with the long tooth in the central driver, and the axial lugs on each holdout ring must mate with the center cam slots.
Spring
Detroit Locker® differentials have two identical springs. Their primary function is to ensure proper return of the driven clutches to the central driver. The spring is not utilized to hold the driven clutches and central driver together. (The central driver and driven clutches have a five-degree negative angle on their teeth which serves to hold the two components together.) Thus, replacement of springs will not correct erratic disengagement of the driven clutches and central driver.
The large diameter of the spring bears against the outer face of the driven clutch and the small diameter of the spring bears against the spring retainer, maintaining pressure against the driven clutch. As their name implies, external springs are visible when the Detroit Locker® differential is bolted together.
Spring Retainer
Detroit Locker® differentials have two identical spring retainers, which serve as shoulders for the springs.
Detroit Locker® differentials with external springs use retainers that slip over the external splines of the side gears and seat against their external flanges. The spring retainer is positioned so that the spring seats in the concave rim of the spring retainer.
Side Gear
Detroit Locker® differentials have two side gears that are splined internally to accept the axle shafts. The hub of the side gear is installed in the bore of the differential case assembly. The external splines of the side gears engage the internal splines of the driven clutch assemblies.
Preload Dampener Kit
The preload dampener kit consists of three belleville springs, a thrust block and a snap ring. Three belleville springs are installed in parallel into the side gear counterbore with the concave side of the springs facing downward into the counterbore. When assembling the thrust block into the side gear, the side with the oil slots must be visible. The snap ring is used to hold all the components inside the side gear during final assembly.
Thrust Washer
Detroit Locker® differentials with preload have two (2) thrust washers located at each end of the differential assembly. The thrust washers have two tabs or ears on them and fit into special slots inside the differential case to prevent rotation and unnecessary wear. The oil grooves stamped into one side of each thrust washer must be visible when installed in the case bore slots.
Differential Case Assembly
A differential case assembly manufactured by Tractech is supplied with Detroit Locker® differentials. The differential case assembly is splined internally to accept the central driver. The differential case is machined to accept the thrust washer tabs and the side gear hub. Match numbers are stamped on the outside diameter of each case half to ensure proper alignment during final assembly.
Backlash
The Tractech Detroit Locker® differential is designed to have mean backlash of 6.7 degrees, which when multiplied by the axle ratio gives a system backlash at the driveshaft end yoke of 30 ± 6 degrees. This is about one-tenth of a revolution in the maximum case tolerance stackup. This backlash is built into the system for proper operation and it is not adjustable.
See also:
What's the DIFF? 
