Note: If you're likely to change your rear diff fluid yourself, (or you intend on starting the diff up for assistance) before you let the fluid out, make sure the fill port can be opened. Nothing worse than letting liquid out and having no way to getting new fluid back in.
FWD final drives are very simple compared to RWD set-ups. Almost all FWD engines are transverse installed, which implies that rotational torque is established parallel to the direction that the tires must rotate. You don't have to alter/pivot the direction of rotation in the final drive. The ultimate drive pinion gear will sit on the finish of the result 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 ring gear will have helical cut teeth just like the rest of the transmitting/transaxle. The pinion equipment will be smaller and have a lower tooth count compared to the ring gear. This produces the ultimate drive ratio. The ring equipment will drive the differential. (Differential procedure will be explained in the differential section of this article) Rotational torque is sent to the front wheels through CV shafts. (CV shafts are commonly known as axles)
An open differential is the most typical type of differential within passenger vehicles today. It is certainly a simple (cheap) design that uses 4 gears (occasionally 6), that are known as spider gears, to operate a vehicle the axle shafts but also allow them to rotate at different speeds if required. “Spider gears” is definitely 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 aspect gears. The differential case (not casing) receives rotational torque through the ring gear and uses it to drive the differential pin. The differential pinion gears ride on this pin and are driven by 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 traveling in a straight line, there is absolutely no differential action and the differential pinion gears only will drive the axle part gears. If the vehicle enters a change, the external wheel must rotate faster than the inside wheel. The differential pinion gears will begin to rotate because they drive the axle side gears, allowing the outer wheel to speed up and the within wheel to slow down. This design is effective provided that both of the driven wheels have traction. If one wheel does not have enough traction, rotational torque will follow the path of least level of resistance and the wheel with little traction will spin while 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 actions allowed. If one wheel begins spinning excessively faster compared to the other (more so than durring regular cornering), an LSD will limit the quickness difference. That is an benefit over a regular open differential design. If one drive wheel looses traction, the LSD actions allows the wheel with traction to get rotational torque and invite the vehicle to go. There are several different designs currently used today. Some are better than others based on the application.
Clutch style LSDs derive from a open up differential design. They possess a separate clutch pack on each of the axle part gears or axle shafts inside the final drive housing. Clutch discs sit between your axle shafts' splines and the differential case. Half of 
the discs are splined to the axle shaft and others are splined to the differential case. Final wheel drive Friction materials is used to split up the clutch discs. Springs put pressure on the axle side gears which put strain on the clutch. If an axle shaft really wants to spin quicker or slower than the differential case, it must conquer the clutch to take action. If one axle shaft attempts to rotate quicker compared to the differential case then your other will try to rotate slower. Both clutches will resist this step. As the quickness difference increases, it becomes harder to get over the clutches. When the vehicle is making a good turn at low velocity (parking), the clutches offer little resistance. When one drive wheel looses traction and all of the torque would go to that wheel, the clutches level of resistance becomes a lot more obvious and the wheel with traction will rotate at (close to) the swiftness of the differential case. This kind of differential will most likely require a special type of fluid or some type of additive. If the liquid isn't changed at the proper intervals, the clutches can become less effective. Leading to small to no LSD action. Fluid change intervals vary between applications. There can be nothing incorrect with this design, but keep in mind that they are only as strong as an ordinary open differential.
Solid/spool differentials are mostly found in drag racing. Solid differentials, just like the name implies, are totally solid and will not really enable any difference in drive wheel swiftness. The drive wheels generally rotate at the same speed, even in a switch. This is not a concern on a drag competition vehicle as drag automobiles are generating in a directly line 99% of the time. This may also be an advantage for cars that are getting set-up for drifting. A welded differential is a normal open differential that has acquired the spider gears welded to make a solid differential. Solid differentials certainly are a fine modification for vehicles made for track use. For street make use of, a LSD option will be advisable over a solid differential. Every change a vehicle takes may cause the axles to wind-up and tire slippage. This is most apparent when driving through a sluggish turn (parking). The effect is accelerated tire wear in addition to premature axle failing. One big benefit of the solid differential over the other types is its power. Since torque is applied directly to each axle, there is no spider gears, which are the weak point of open differentials.
