Note: If you are likely to change your rear diff liquid yourself, (or you plan on opening the diff up for program) before you allow fluid out, make certain the fill port can be opened. Nothing worse than letting fluid out and then having no way of getting new fluid back in.
FWD last drives are very simple in comparison to RWD set-ups. Almost all FWD engines are transverse installed, which means that rotational torque is created parallel to the direction that the wheels must rotate. You don’t have to change/pivot the path of rotation in the final drive. The final drive pinion gear will sit on the finish of the output shaft. (multiple output shafts and pinion gears are possible) The pinion equipment(s) will mesh with the final drive ring gear. In almost all cases the pinion and band gear will have helical cut the teeth just like the rest of the transmission/transaxle. The pinion equipment will be smaller and have a much lower tooth count than the ring equipment. This produces the final drive ratio. The ring gear will drive the differential. (Differential procedure will be explained in the differential portion of this article) Rotational torque is sent to the front tires through CV shafts. (CV shafts are generally referred to as axles)
An open differential is the most common type of differential within passenger vehicles today. It is a very simple (cheap) design that uses 4 gears (occasionally 6), that are referred to as spider gears, to drive the axle shafts but also permit them to rotate at different speeds if necessary. “Spider gears” is a slang term that’s commonly used to describe all the differential gears. There are two various kinds of spider gears, the differential pinion gears and the axle part gears. The differential case (not casing) receives rotational torque through the ring gear and uses it to operate a vehicle the differential pin. The differential pinion gears ride on this pin and so are driven because of it. Rotational torpue can be then transferred to the axle aspect gears and out through the CV shafts/axle shafts to the wheels. If the vehicle is venturing in a straight line, there is no differential actions and the differential pinion gears will simply drive the axle part gears. If the automobile enters a convert, the outer wheel must rotate quicker than the inside wheel. The differential pinion gears will start to rotate because they drive the axle side gears, allowing the outer wheel to increase and the inside wheel to decelerate. This design works well so long as both of the powered wheels possess traction. If one wheel doesn’t have enough traction, rotational torque will observe the road of least level of resistance and the wheel with little traction will spin as the wheel with traction will not rotate at all. Because the wheel with traction isn’t rotating, the vehicle cannot move.
Limited-slip differentials limit the quantity of differential action allowed. If one wheel begins spinning excessively faster than the other (way more than durring normal cornering), an LSD will limit the speed difference. This is an benefit over a regular open differential design. If one drive wheel looses traction, the LSD action will allow the wheel with traction to obtain rotational torque and invite the vehicle to go. There are many different designs currently used today. Some work better than others based on the application.
Clutch style LSDs derive from a open differential design. They possess Final wheel drive another clutch pack on each one of the axle aspect gears or axle shafts in the final drive casing. Clutch discs sit between your axle shafts’ splines and the differential case. Half of the discs are splined to the axle shaft and the others are splined to the differential case. Friction material is used to split up the clutch discs. Springs place pressure on the axle aspect gears which put strain on the clutch. If an axle shaft wants to spin faster or slower compared to the differential case, it must get over the clutch to do so. If one axle shaft tries to rotate quicker than the differential case then the other will attempt to rotate slower. Both clutches will resist this step. As the rate difference increases, it turns into harder to overcome the clutches. When the automobile is making a good turn at low swiftness (parking), the clutches provide little level of resistance. When one drive wheel looses traction and all the torque would go to that wheel, the clutches resistance becomes much more apparent and the wheel with traction will rotate at (close to) the swiftness of the differential case. This type of differential will most likely require a special type of fluid or some kind of additive. If the liquid is not changed at the proper intervals, the clutches may become less effective. Resulting in little to no LSD actions. Fluid change intervals vary between applications. There is nothing incorrect with this style, but remember that they are only as strong as an ordinary open differential.
Solid/spool differentials are mostly found in drag racing. Solid differentials, like the name implies, are completely solid and will not really enable any difference in drive wheel speed. The drive wheels at all times rotate at the same speed, even in a convert. This is not an issue on a drag competition vehicle as drag vehicles are traveling in a straight line 99% of that time period. This can also be an advantage for vehicles that are being set-up for drifting. A welded differential is a regular open differential that has had the spider gears welded to make a solid differential. Solid differentials certainly are a fine modification for vehicles created for track use. For street use, a LSD option will be advisable over a solid differential. Every switch a vehicle takes will cause the axles to wind-up and tire slippage. This is most noticeable when generating through a 
gradual turn (parking). The result is accelerated tire wear along with premature axle failure. One big benefit of the solid differential over the other styles is its power. Since torque is used directly to each axle, there is no spider gears, which will be the weak spot of open differentials.
