Note: If you are going to change your back diff fluid yourself, (or you plan on starting the diff up for support) before you allow fluid out, make sure the fill port could be opened. Nothing worse than letting liquid out and having no way to getting new fluid back in.
FWD last drives are very simple in comparison to RWD set-ups. Almost all FWD engines are transverse mounted, which means 
that rotational torque is created parallel to the path that the tires must rotate. There is no need to change/pivot the direction of rotation in the ultimate drive. The ultimate drive pinion gear will sit on the end of the result shaft. (multiple output shafts and pinion gears are possible) The pinion equipment(s) will mesh with the final drive ring equipment. In almost all situations the pinion and band gear could have helical cut the teeth just like the remaining 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 band equipment will drive the differential. (Final wheel drive differential operation will be described in the differential section of this article) Rotational torque is sent to the front tires through CV shafts. (CV shafts are commonly known as axles)
An open up differential is the most common type of differential found in passenger vehicles today. It is certainly a simple (cheap) style that uses 4 gears (sometimes 6), that are referred to as spider gears, to operate a vehicle the axle shafts but also allow them to rotate at different speeds if required. “Spider gears” is a slang term that’s commonly used to spell it out all of 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 equipment and uses it to drive the differential pin. The differential pinion gears ride upon this pin and are driven because of it. Rotational torpue is certainly then transferred to the axle part gears and out through the CV shafts/axle shafts to the wheels. If the automobile is travelling in a directly 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 external wheel must rotate faster than the inside wheel. The differential pinion gears will start to rotate as they drive the axle side gears, allowing the external wheel to increase and the within wheel to decelerate. This design works well provided that both of the driven wheels have traction. If one wheel does not have enough traction, rotational torque will follow the road of least resistance and the wheel with small traction will spin while the wheel with traction will not rotate at all. Since the wheel with traction is not rotating, the vehicle cannot move.
Limited-slip differentials limit the amount of differential actions allowed. If one wheel starts spinning excessively faster than the other (way more than durring regular cornering), an LSD will limit the velocity difference. That is an benefit over a regular open differential style. If one drive wheel looses traction, the LSD action allows the wheel with traction to obtain rotational torque and allow the vehicle to move. There are several different designs currently in use today. Some work better than others depending on the application.
Clutch style LSDs derive from a open differential design. They possess another clutch pack on each one of the axle aspect gears or axle shafts inside the final drive housing. Clutch discs sit down 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. Friction material is used to separate the clutch discs. Springs place strain on the axle side gears which put strain on the clutch. If an axle shaft wants to spin quicker or slower compared to the differential case, it must overcome the clutch to do so. If one axle shaft attempts to rotate faster compared to the differential case then the other will try to rotate slower. Both clutches will resist this step. As the speed difference increases, it becomes harder to conquer the clutches. When the vehicle is making a good turn at low rate (parking), the clutches offer little resistance. When one drive wheel looses traction and all the torque would go to that wheel, the clutches resistance becomes much more obvious and the wheel with traction will rotate at (close to) the rate of the differential case. This kind of differential will likely require a special type of liquid or some form of additive. If the fluid isn’t changed at the proper intervals, the clutches may become less effective. Leading to little to no LSD action. Fluid change intervals vary between applications. There is usually nothing incorrect with this design, 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 totally solid and will not enable any difference in drive wheel swiftness. The drive wheels always rotate at the same rate, even in a switch. This is not an issue on a drag competition vehicle as drag automobiles are traveling in a straight line 99% of that time period. This may also be an edge for vehicles that are being set-up for drifting. A welded differential is a regular open differential that has got the spider gears welded to make a solid differential. Solid differentials certainly are a great modification for vehicles made for track use. As for street use, a LSD option will be advisable over a solid differential. Every change a vehicle takes will cause the axles to wind-up and tire slippage. That is most obvious when generating through a slower turn (parking). The result is accelerated tire put on and also premature axle failure. One big benefit of the solid differential over the other styles is its strength. Since torque is used right to each axle, there is no spider gears, which will be the weak spot of open differentials.