Note: If you’re likely to change your rear diff fluid yourself, (or you intend on opening the diff up for support) before you allow fluid out, make certain the fill port can be opened. Nothing worse than letting fluid out and then having no way to getting new fluid back.
FWD final drives are extremely simple compared to RWD set-ups. Virtually all FWD engines are transverse mounted, which means that rotational torque is established parallel to the direction that the wheels must rotate. There is no need to modify/pivot the path of rotation in the ultimate drive. The ultimate drive Final wheel drive pinion equipment will sit on the finish of the result shaft. (multiple output shafts and pinion gears are possible) The pinion gear(s) will mesh with the ultimate drive ring equipment. In almost all cases the pinion and band 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 than the ring equipment. This produces the ultimate drive ratio. The band equipment will drive the differential. (Differential procedure will be explained in the differential section of this article) Rotational torque is delivered to the front tires through CV shafts. (CV shafts are commonly known as axles)
An open up differential is the most typical type of differential within passenger cars and trucks today. It is definitely a very simple (cheap) style that uses 4 gears (occasionally 6), that are known as spider gears, to operate a vehicle the axle shafts but also permit them to rotate at different speeds if required. “Spider gears” is certainly a slang term that is commonly used to spell it out all the differential gears. There are two different types of spider gears, the differential pinion gears and the axle side 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 trip on this pin and are driven because of it. Rotational torpue can be then used in the axle part gears and out through the CV shafts/axle shafts to the tires. If the automobile is travelling in a directly line, there is no differential action and the differential pinion gears will simply drive the axle part gears. If the automobile enters a convert, the outer 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 increase and the inside wheel to slow down. This design works well as long as both of the powered wheels have got traction. If one wheel doesn’t have enough traction, rotational torque will observe the path of least level of resistance and the wheel with small traction will spin as the wheel with traction will not rotate at all. Because the wheel with traction isn’t rotating, the automobile cannot move.
Limited-slide differentials limit the amount of differential actions allowed. If one wheel starts spinning excessively faster compared to the other (more so than durring normal cornering), an LSD will limit the swiftness difference. That is an advantage over a normal open differential style. If one drive wheel looses traction, the LSD action will allow the wheel with traction to obtain rotational torque and allow the vehicle to go. There are many different designs currently in use today. Some work better than others depending on the application.
Clutch style LSDs derive from a open up differential design. They possess another clutch pack on each one of the axle side gears or axle shafts in the final drive casing. Clutch discs sit down between the 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 separate the clutch discs. Springs place pressure on the axle side gears which put strain on the clutch. If an axle shaft really wants to spin faster or slower compared to the differential case, it must overcome the clutch to do so. If one axle shaft attempts to rotate quicker than the differential case then the other will try to rotate slower. Both clutches will resist this step. As the swiftness difference increases, it turns into harder to overcome the clutches. When the vehicle is making a tight turn at low velocity (parking), the clutches provide little level of resistance. When one drive wheel looses traction and all of the torque goes to that wheel, the clutches level of resistance becomes a lot more obvious and the wheel with traction will rotate at (close to) the velocity of the differential case. This type of differential will most likely need a special type of liquid or some kind of additive. If the fluid is not changed at the proper intervals, the clutches may 
become less effective. Resulting in little to no LSD action. Fluid change intervals vary between applications. There is nothing wrong 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 totally solid and will not enable any difference in drive wheel speed. The drive wheels often rotate at the same speed, even in a change. 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 may also be an edge for vehicles that are being 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 are a fine modification for vehicles made for track use. For street use, a LSD option would be advisable over a good differential. Every turn a vehicle takes may cause the axles to wind-up and tire slippage. This is most apparent when traveling through a sluggish turn (parking). The result is accelerated tire wear and also premature axle failure. One big benefit of the solid differential over the other types is its strength. Since torque is used directly to each axle, there is no spider gears, which are the weak spot of open differentials.
