Note: If you are likely to change your back diff liquid yourself, (or you intend on starting the diff up for services) 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 in comparison to RWD set-ups. Virtually all FWD engines are transverse mounted, which means that rotational torque is created parallel to the direction that the tires must rotate. You don’t have to modify/pivot the direction of rotation in the final drive. The final drive pinion equipment will sit on the end of the result shaft. (multiple result shafts and pinion gears are feasible) The pinion gear(s) will mesh with the ultimate drive ring equipment. In almost all situations the pinion and ring gear will have helical cut the teeth just like the rest of the transmitting/transaxle. The pinion equipment will be smaller and have a much lower tooth count compared to the ring gear. This produces the final drive ratio. The band gear will drive the differential. (Differential operation will be explained in the differential section of this content) Rotational torque is sent to the front wheels through CV shafts. (CV shafts are generally known as axles)
An open differential is the most typical type of differential found in passenger vehicles today. It is certainly a very simple (cheap) design that uses 4 gears (sometimes 6), that are known as spider gears, to drive 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 the differential gears. There are two various kinds of spider gears, the differential pinion gears and the axle aspect gears. The differential case (not housing) gets rotational torque through the band equipment and uses it to operate a vehicle the differential pin. The differential pinion gears trip on this pin and so are driven by it. Rotational torpue is definitely then used in the axle aspect gears and out through the CV shafts/axle shafts to the tires. If the vehicle is travelling in a straight line, there is no differential action and the differential pinion gears will simply drive the axle aspect gears. If the vehicle enters a switch, the external wheel must rotate quicker 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 as long as both of the powered wheels have traction. If one wheel does not have enough traction, rotational torque will observe the road of least resistance and the wheel with little traction will spin while the wheel with traction won’t rotate at all. Since the wheel with traction isn’t Final wheel drive rotating, the automobile cannot move.
Limited-slip differentials limit the amount of differential action allowed. If one wheel starts spinning excessively faster than the other (way more than durring normal cornering), an LSD will limit the rate difference. This is an benefit over a normal open differential style. If one drive wheel looses traction, the LSD action allows 
the wheel with traction to obtain rotational torque and invite the vehicle to go. There are several different designs currently in use today. Some are better than others based on the application.
Clutch style LSDs derive from a open differential design. They have another clutch pack on each one of the axle part 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 materials is used to split up the clutch discs. Springs place strain on the axle side gears which put pressure on the clutch. If an axle shaft wants to spin faster or slower than the differential case, it must overcome the clutch to take action. If one axle shaft attempts to rotate quicker compared to the differential case then the other will try to rotate slower. Both clutches will resist this step. As the acceleration difference increases, it turns into harder to get over the clutches. When the vehicle is making a good turn at low quickness (parking), the clutches offer little resistance. When one drive wheel looses traction and all of the torque goes to that wheel, the clutches resistance becomes a lot more obvious and the wheel with traction will rotate at (close to) the swiftness of the differential case. This type of differential will likely require a special type of fluid or some kind of additive. If the fluid isn’t changed at the correct intervals, the clutches may become less effective. Leading to little to no LSD actions. Fluid change intervals differ between applications. There is nothing incorrect with this design, but remember that they are just 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 really allow any difference in drive wheel speed. The drive wheels generally rotate at the same quickness, even in a turn. This is not an issue on a drag race vehicle as drag automobiles are generating in a directly line 99% of that time period. This may also be an advantage for vehicles that are getting set-up for drifting. A welded differential is a regular open differential which has got the spider gears welded to make a solid differential. Solid differentials certainly are a great modification for vehicles created for track use. As for street make use of, a LSD option would be advisable over a solid differential. Every convert a vehicle takes may cause the axles to wind-up and tire slippage. That is most obvious when traveling through a gradual turn (parking). The result is accelerated tire use in addition to premature axle failing. One big benefit of the solid differential over the other types is its strength. Since torque is applied right to each axle, there is no spider gears, which will be the weak point of open differentials.
