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How often should I change my transmission fluid?(WIP)

What does a limited-slip differential do?


The job of the drive wheels are to move the car, and it seems logical that more wheels that are supplied torque the more traction will be available to accelerate the car. If all we did was drive in a straight line, we could connect the drive wheels with a solid axle, slap a ring gear on it, and turn it with the pinion coming off the driveshaft. This is not too far from the basic idea of a “spool.” But when a car corners, the wheels on each side must travel different distances. The inside wheel has less ground to cover than the outside wheel. With the above mentioned setup, either the inside wheel would slip along the pavement as it spun too fast, the outside wheel would slip along the pavement as it spun too slow, or some combination of both. Or perhaps the axle would break from the stress. Enter the differential. A device that derives its name from the ability to allow the drive wheels to operate at a speed differential.

Open Differential

The most common and simple type of differential that is found on a wide variety of cars is known as the Open Differential. In this system, the input pinion at the tail of the driveshaft spins a ring gear that is perpendicular to it (as an aside, it is the ratio of teeth on the ring gear to the input pinion that determines the “rear end ratio”). This ring gear is connected to mounting points of two pinion gears. These mounts are referred to as the cage. The pinion gears mesh with the side gears that are on the end of each axle, but are free to spin in their mounts to the ring gear. When both wheels are on the pavement and the vehicle is traveling straight, the input pinion spins the ring, which causes the cage to rotate with it. Because the car is traveling straight, both wheels must rotate at the same speed. Therefore, the pinion gears do not spin in their housings, and both wheels are driven equally, effectively locked to the cage.

In a corner, the wheels have to spin at different speeds. The grip of the tires on the road prevents the wheels from slipping, so the pinion gears must spin in their mounts. In this situation, the axles are not locked to the cage, but allowed to slip. In a way, it is the wheels traveling at different speeds that allow the differential to function and not the other way around. The “direction” that one wheel slips, relative to the cage, is opposite to the “direction” that the other will slip. This makes sense since we know that one wheel must travel faster than the other one.

So what if one wheel loses its grip? Remember, the pinion gears are free to spin in the cage. This means that there is practically no limit to the slip that each axle can have with respect to the cage. Additionally, because of its design the open differential supplies the same amount of torque to each wheel. But, this amount of torque that is delivered to both wheels depends on the amount of traction. Maximum torque is available only when both wheels are spinning at the same speed because they are locked to the cage. When one wheel loses traction, it wants to spin faster than the other one. The other wheel doesn’t want to spin any faster because it has plenty of grip. So the pinion gears begin to spin. The tire that lost traction is free to slip as much as it wants, but torque is cut to both wheels.

Most people think that when one wheel is spinning with an open differential that the other wheel is getting no torque. This is due to seeing the open differential in action with one wheel stuck in the mud or ice while the other one has some traction. Remember that as stated above the open differential always supplies an equal amount of torque to each wheel. When you have one wheel stuck in the mud and the other has traction, the muddy tire is free to spin very quickly. Since there is very little traction, there is little load and little torque is required. The wheel with traction receives the same miniscule amount of torque, but it is usually not enough to propel the vehicle forward and the car remains stationary.

Locking Differentials

Sometimes referred to simply as lockers, these differentials contain a mechanism that will lock pinions and therefore the axles to the cage to prevent slipping. The mechanism may be electric, hydraulic, or pneumatic. It may be controlled manually, or it may operate automatically. They are very popular among off-road circles and it isn’t hard to imagine why. There are many situations in which the wheels could see differing traction, and an open differential would be constantly slipping and reducing available torque. And because the axles are locked, if one wheel comes off the ground, both will still rotate at the same speed. This is the only differential that will allow this.

When unlocked, they perform like an open differential. However, users may typically notice clicking noises when cornering, which is a side effect of the design. If you are cornering and the inside wheel lifts, it could potentially lose traction and you will then lose torque to both drive wheels. You may be tempted to lock the differential in that situation, but that could result in unpredictable results (like hitting a wall).

Limited Slip Differentials

Limited Slip Differentials (LSD for short) are an attempt to remedy the problems that an open differential has when the drive wheels do not have the same traction. This applies not only during launches, but also in cornering. The two types of mechanical LSDs are Clutch Based and Gear Based. There is a fluid based LSD known as a Viscous Coupling, and there are Electronically controlled LSDs, but neither will be covered as there are none for available for our applications.

Clutch Based

These are the more common types of LSDs and were produced much earlier than the gear based type. Different manufacturers marketed them differently, but Chevrolet’s label of Positraction became the most famous and so clutch based are often affectionately referred to as “posi.” During typical operation, posi performs like an open differential and is similar in construction. But there are a few important differences.

Within the differential there are two clutches, one for each side gear, and a mechanism to detect slip and apply the gears to the clutches. When one wheel begins to slip, the spring pack applies force on the side gear of the wheel with traction and it is pressed against the clutch. The clutch is connected to the cage, and the friction generated increases the torque applied to the wheel with traction. The extra torque applied is proportional to the force needed to overcome the clutch, which in turn depends on the clutch and the stiffness of the spring. But the main limitation of the clutch differential is that you are still losing torque in this situation, but fortunately not nearly as much as with an open differential. Additionally, the clutch operation may not always be seamless, which could lead to some suspense around corners. Lastly, another limitation is that the clutches will eventually wear out.

You may have heard of 1, 1.5, or 2 way differentials. In a 1 way differential, the center cam is designed in such a way that it can apply the gear to the clutch only under acceleration. In a 1.5 way, it can apply in both acceleration and deceleration, but takes twice as much slip to apply during deceleration. A 2 way provides the same limited slip effect in acceleration and deceleration (although typically it is a little less during deceleration).

Eaton and Auburn make popular clutch based differentials that tend to be very durable. One of the reason clutch based units are still produced is that there are a wide variety of units rated to take the torque in high power applications.

Gear Based

Vernon Gleasman invented the Torsen (Torque Sensing) differential in 1958, although it was not marketed until 1982. The Torsen is a gear based LSD with many advantages over the clutch based system. The Torsen uses a helical planetary gear set to sense slip. When one wheel begins to lose traction, the Torsen can transfer torque to the stickier side. A big advantage of the Torsen is that not only can it distribute torque unevenly, but it will always transfer more torque to the wheel with traction and it does so before slipping actually occurs. The amount that it transfers depends on the torque bias built into the unit. The OEM Torsen in Fbodies (T2) has a torque bias of 2:1. The beefier T2R unit has a bias ratio of 4:1. Torsen differentials used on the HMMWV have a bias of 5:1. The higher the torque bias, the less likely you are to do a one wheel burnout, but it does make the car less forgiving (albeit faster if driven properly) in the corners.

Detroit Locker (part of Eaton now) makes a gear based unit called the TrueTrac. It similar in operation to the Torsen and has a torque bias of 3.5:1. It is stronger than the OEM Torsen.

An oddity of the Torsen occurs when one wheel has no traction, like if one wheel is off the ground completely. Because the amount of torque delivered depends on the torque bias ratio, and because the wheel in the air has no load and is getting zero torque, the Torsen cannot transfer any torque to wheel on the ground (transferred torque equals 2 times 0). If you are in this situation, you can load the wheel by applying the brakes, and the differential will resume supplying torque.

For a visual demostration of how an open differential works, try watching the animations available at this link: http://auto.howstuffworks.com/differential3.htm

What are the benefits of an aftermarket torque converter?(WIP)

Should I install a transmission cooler on my car?

Although this modification comes into debate, the answer is yes. The argument against transmission coolers is that they are dead weight, offering no performance advantage. Although a transmission cooler does not offer direct advantages, a transmission cooler does exactly what the name implies- it cools your automatic transmission. With a stock setup on a car that does not hit the track often, a transmission cooler would be little more than something to add life to your transmission. However, ANY car with a torque converter NEEDS to have a transmission cooler. Torque converters are capable of burning through an improperly cooled transmission very quickly. They are cheap and the weight is insignificant to the car.

What rear-end gears should I run?(WIP)

My stock clutch (M5) is going out. What should I replace it with?(WIP)

F-Body: Can I use an aluminum LS1 drive shaft on my V6 car?

The answer is yes. The LS1 aluminum driveshaft is fully compatible with ALL 1984 to 2002 F-Bodies as long as it had a 5 or 6 speed manual, the 700r4 automatic, or the 4L60E automatic transmissions. That means it will fit ALL fourth generation V6 F-Bodies. The aluminum driveshaft offers increased performance through weight reduction. Rotational mass has the biggest effect on performance hindrance in a car, so lightening the weight of the driveshaft is always a plus. The 1LE aluminum driveshaft (the aluminum driveshaft from the LS1) weighs 10 pounds. The stock 1-piece steel driveshaft weighs 22 pounds. The stock 2-piece steel driveshaft weighs 25 pounds.

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