Differential Types


There were several types of differentials available from Ford, in the rear ends, over the years. Types included: Conventional, Limited-Slip, Traction-Lok, and Detroit-Locker. (Notice the term "Posi" was never used. --that's a nasty Chevrolet term!).

2-pinion conventional differential (left) compared to 4-pinion Traction-Lok differential (right). Notice "shrouding" around ring gear bolt holes on Traction-Lok differential and the "flat" area around the ring gear bolt holes in the conventional differential.

2-pinion conventional differential (left) compared to 4-pinion Traction-Lok differential (right).

Inside of 2-pinion conventional differential (left) and inside of 4-pinion Traction-Lok differential (right)


The most basic, as well as the most common type of differential, is the Conventional style differential (also known as a "Single-track"). This is the oldest type of differential which is still commonly used today. With the Conventional, the wheel of the car which first grips under load (the load in this case being the road surface) transfers the power to the opposite wheel. This is never noticed in normal driving where both wheels share the load equally, but during hard acceleration, cornering, or less-than-desirable driving surfaces (snow, ice, or gravel), one wheel will grip the road and the other will spin. This slippage makes the Conventional differential inadequate for high-performance use.
This assembly was available with either Ford's intergral or removable carrier assemblies. Generally, Ford integrals with Conventional differentials can come equipped with 7 ¼ through 8-inch ring gears (years '65-'73), while removable models used ring gear sizes ranging from 7 ¾ to 9-inches. 

LIMITED-SLIP DIFFERENTIALS: (Closed differential) 

This type of Ford differential uses four steel clutch plates which are locked into the differential cover. Three bronzed-bonded clutch plates are splined to a clutch hub, which, in turn, is splined to the left-hand axle shaft. A belveled spring plate provides constant pressure between the steel and the bonded clutch plates, assuring that the clutch is always engaged. This provides equal disbursment of power to both wheels. (In the very early model Ford trucks, this Limited-Slip differential was called an "Equa-lock"). Differential action between wheels is accomplished through clutch plate slippage. 
Limited-slip differentials were available on a few intergrals with 3.20:1 or 3.50:1 gearing. Generally, gear sizes of 7 ¼ through 8-inches were utilized. However, as stated before, this type of rear is not really suited for true performance work. By contrast, the removable carrier was commonly equipped with the Limited-Slip and generally uses gear sizes of 7 ¾ through 9-inches, in conjunction with gear ratios of 2.80:1 through 4.30:1. Differences in ring gear sizes occured depending on the engine size used and the year of the car (1965-1973).
Although there are several gear set sizes available with the removable carrier cases, the 9-inch ring gear is considered the "ultimate" from a high-performance/competition standpoint. The smaller 8 through 8 ¾-inch ring gear equipped rear ends are aduqate enough to hold up to the stock engines that were originally installed in front of them, but if engine tweaking becomes more serious, it can easily put the performace of the otherwise stock engine beyond what these smaller rear ends are capable of handling.


This type, although very similar to the Ford Limited-Slip differential, has some important differences. Both types employ a multi-clutch plate system for positive locking action. (the Limited -Slip has three clutch plates while the Traction-Lok has more surface area with four clutch plates). In turning, the Limited-Slip model allows differential action by slipping the clutch plates. This produces a noise level higher than with Conventional differential types. 
The Traction-Lok differential uses a pre-load spring plate and center block between the pinion gears (sometimes refered to as "spider gears") and side gears. It has (4) pre-loaded tension springs which release the pinion gears to rotate only under precalculated side gear loads. Therefore, the clutch plates remain engaged at all times, and are never required to slip for differential purposes. The result is a much improved, quieter operation during turns. 
Traction-Lok is considered the best all-around street differential for Fords. Beginning in 1969, the Traction-Lok differential system was made available on removable carrier systems only, and after '69, it replaced the older style Limited-Slip units in the 9-inch rear ends. These Traction-Lok differentials cannot be inserted into the intergral carrier. All Traction-Loks utilize the 9-inch ring gear. 

4-pinion Traction-Lok differential with example of 4-pinion arrangement assembled outside of differential case, as well as "exploded" view of 4-pinion block, cross shafts, springs & spring cover plate.


Whereas the standard 9-inch Ford removable carrier is completely adequate for street machines (even when the stock engine is slightly modified), constant racing usage requires something extra in the area of strength and durability. The Detroit-Locker is designed for racing purposes...Period! 
The Detroit-Locker uses a super-strong splined ring-clutch system which provides positive engagement at all times. Differential action is accomplished via a ratchet tooth-jumping mechanism which is primitive yet highly effective. This mechanism provides the very distinctive trademark "clunking" noises heard in turns which have made the locker famous. Considering that the optional Limited-Slip or Traction-Lok will accomplish virtually everything a Detroit-Locker does, lockers are really not practical for street use. 
The Detroit-Locker was an over-the-counter replacement which could be installed by a Ford dealer. They were designed for the 9-inch removable carrier assembly only and cannot be interchanged with integrals. 


All big-block Mustangs came with the removable carrier type using gear sizes of 8 ¾ or 9-inches (1967-1973). The 427 and 428 engines were always mated to 9-inch ring gear (all years) while some 1967 and 1968 390 GT Mustangs came with 8 ¾-inch ring gears, and others used 9-inch gears when an optional gear ratio was ordered. High performance 289, 302, and 351 Windsors all used removable carrier rears with ring gears ranging from 8 ¾-inches (1965-1966) to both 8 ¾ and 9-inches in later years (1967-1973). Standard 2-barrel, 289, 302 and all 6-cylinders used ring gears varying from 7 ¾ to 8 ¾ inches, and, as previously stated, some combinations used the non-desirable integral rears. 


The Ford differentials, whether a Conventional style or Traction-Lok style, came in either two or four-pinion configurations. The slang-term most often heard for these pinion gears is "spider gears". 
The four pinion setup is clearly stronger than the two pinion derivatives because the load is spread out over a greater surface area. 
It is interesting to note that while BOTH the Conventional & Traction-Lok differentials were available in either two or four pinion arrangements, the Limited-Slip was a two pinion differential ONLY.