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Question: Rear end
What is the difference between a posi, trac-loc, Detroit locker and
limited slip differential as applied to a '71 Mustang with toploader?


[Image: 1_11_11_13_11_50_27.png]
from this link http://www.f150forum.com/f38/differentia...ed-118873/
I found the following to be helpful. See a video after this text below.

Types of Differentials
Differentials can be generally classified into 4 categories. Open Differentials, Limited Slip Differentials, Locking Differentials and Spools. Spools are really just the elimination of the differential, so really, there are three categories.
Beyond the open differential, the various types of "non-open" differentials will provide varying degrees of limiting of the spin or slip of an open differential. What also varies is the feel of these differentials, which translates into varying degrees of handling characteristics on road and offroad.
Open / Standard Carrier Differential

The standard differential, or what is referred to as an open carrier, is what comes with most OEM vehicles. The open carrier holds the ring gear in place and within the open carrier is generally a set of gears called spider gears. These spider gears are responsible for allowing a vehicle to negotiate a turn and allow the outside wheel to travel farther and turn faster than the inside wheel. This type of open design works great for most of vehicles on the road today. However when a vehicle with an open differential meets a lack of traction, it directs power to the wheel with the least amount of resistance. The result is the wheel on the traction-less surface spins free, while the opposite wheel of that axle on the better traction surface provides little or no power.
Limited Slip Differentials, Posi-Traction (Posi, Posis)
Limited Slip and positraction (posi) differentials are designed to "limit" the tendency of open differential to send power to a wheel that lacks traction and redirect the power to a degree to the other wheel of the axle. The Limited Slip and Positraction differential will send power to both wheels equally when traveling straight, however when one wheel spins due to a lack of traction, the differential will automatically provide torque to the other wheel with traction. Limited Slip and Positraction (posi) differentials limit the loss of torque to a slipping wheel through various mechanisms such as clutches, gears cones, and other methods dependant on the unit. The limited slip and positraction will not provide 100% lock up of the differential in extreme situations such as when a wheel completely looses traction. Limited Slip and Positraction (posi) differentials are recommended for daily driven vehicles and are used in many applications where traction is sometimes needed as in emergency vehicles. They are also ideal for front axles of 4x4 vehicles that are not equipped with front hubs that can be disengaged. The term "positraction" ("posi" for short) was used by General Motors years ago for their limited slip differential and has been used to refer to limited slips since.
Lockers, Locking Differentials
A locking differential or "Locker" uses a mechanism that allows left and right wheels to "lock" relative to each other and turn at the same speed regardless of which axle has traction and regardless of how little traction a slipping wheel has. In this state, the axle acts more as a "Spool". This means traction can be sent to a wheel that may be planted firmly on the ground while the other wheel of the axle is completely off the ground. In this situation an open differential will spin the free (lifted) wheel sending absolutely no torque to the wheel in the ground. A limited slip in this situation will send some torque to the wheel on the ground but possibly no enough to provide any forward momentum.
Lockers use various mechanisms to provide lock-up and can be divided into two categories, Automatic Lockers and On-Command, or selectable Lockers.
Automatic Lockers:
Automatic locking differentials are designed to lock both wheels of an axle automatically when torque is applied so that both wheels are providing power. When torque is not being applied such as when the clutch is press down, the differential is allowed to unlock, permitting a variance in wheel speed while negotiating turns. Automatic lockers tend to create odd handling characteristics on the street as they lock and unlock and take some getting used to.

On-Command Lockers (Selectable, Manually Operated):
On-command lockers are the best of both worlds providing the benefits of a locking differential and an open differential. An on-command locker uses a switch activated electric motor or vacuum diaphragm or a cable / lever to engage the locker. When an on-command locker is not engaged, it acts like a standard open differential with none of the quirky handling characteristics of an automatic locker. When the on-command locker is engaged, the differential locks the axle shafts together where it is now more like a spool with no differential of speed between the wheels of that axle. Some OEM on-command locker designs are available on the market including 1998 and newer Toyota Tacoma and Land Cruiser and the Jeep TJ and JK Rubicons.

Spools, Mini Spools
Spools are actually the lack of a differential. Spools are a 100% lock-up between both wheels of an axle all the time. Spools are generally used for racing and serious offroad use where little or no street driving is seen by the vehicle and a stronger, lighter rear end is needed.



1971 Boss 351  
1972 Q code 4 speed convertible 
1971 Mustang Sportsroof  351-2V FMX 
1973 Mach 1 (parts car)
The most commonly known locking differential is the Detroit Locker, which acts pretty much like a spool when it locks. It is also the one that clicks (ratchets) when turning and not locked. My '71 has a hard shifting C6 and a Detroit Locker and things can get exciting when I'm turning with a heavy foot and it shifts from 1st to 2nd and the locker turns the differential into a "spool".
The Torsen is also a mechanical unit, but uses gears to multiply the torque to the wheel that has traction.
Trac-Loc is Ford's name for the clutch type limited slip differential, the posi name comes from GM's version.

“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
All good info above. For a street driven performance Ford car a T-Loc is great. In reality an open rear works fine unless you regularly launch your car at every stop.

Previous to T-Loc Ford called it Equa-Loc. I think it changed names in 68.

[Image: 386_07_10_13_5_58_42.jpeg]
My Mustangs:
71 M-code Mach 1, Medium Blue/White Sport, 4R70W, 3L50, Factory Ram Air.
72 Q-code Mach 1, Pewter/Black Sport, 4-spd, 3L25.
65 Convertible, Britney Blue/White/White, more modified than original.
05 Convertible, Legend Lime/Tan/Tan, future classic??
According to Marti my car came with a "9", 3.25 standard axle ratio.
What would I be looking for as a replacement?


[Image: 1_11_11_13_11_50_27.png]
goodnigh;88297 Wrote:According to Marti my car came with a "9", 3.25 standard axle ratio.
What would I be looking for as a replacement?

...an "open" rear end if you are going back to "original."


Do the RIGHT thing.
cobra3073;88299 Wrote:...an "open" rear end if you are going back to "original."


Don of OMS may have something for me.
That would mean nearly half this car came
from Don Cool


[Image: 1_11_11_13_11_50_27.png]
Don't feel bad I told him his boys can fight it out as to which one I'll be putting through college by the time I'm done! Tongue

[Image: 2rr7aiv.png]

Just cruising along minding our own business when BAM!!! The LAWS show up.
I have the Detroit TruTrac in my '68. It's set up for road racing and driving on the street. It's very durable, handles a ton of power and is very smooth in the corners. I suppose it depends in your intended purpose.
THe detroit locker is much better suited for straight road driving. Its a little unruly for the hills and turns of East Tn.
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