Final wheel drive

Note: If you are likely to change your back diff liquid yourself, (or you intend on opening the diff up for assistance) before you let the fluid out, make sure the fill port can be opened. Absolutely 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 mounted, which implies that rotational torque is established parallel to the direction that the tires must rotate. You don’t have to modify/pivot the path of rotation in the ultimate drive. The ultimate drive pinion equipment will sit on the end of the output shaft. (multiple result shafts and pinion gears are possible) The pinion gear(s) will mesh with the ultimate drive ring gear. In almost all instances the pinion and ring gear will have helical cut the teeth just like the remaining tranny/transaxle. The pinion gear will be smaller sized and have a lower tooth count than the ring equipment. This produces the final drive ratio. The ring gear will drive the differential. (Differential operation will be explained in the differential portion of this article) Rotational torque is delivered to the front wheels through CV shafts. (CV shafts are commonly referred to as axles)
An open up differential is the most common type of differential within passenger vehicles today. It is usually a very simple (cheap) design 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” can be a slang term that is commonly used to spell it out all of the differential gears. There are two different types of spider gears, the differential pinion gears and the axle part gears. The differential case (not casing) gets rotational torque through the band equipment and uses it to drive the differential pin. The differential pinion gears ride on this pin and 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 tires. If the vehicle is travelling in a directly line, there is absolutely no differential actions and the differential pinion gears will simply drive the axle aspect gears. If the vehicle enters a change, the external wheel must rotate faster compared to the inside wheel. The differential pinion gears will begin to rotate because they drive the axle side gears, allowing the external wheel to increase and the within wheel to slow down. This design works well so long as both of the powered wheels possess traction. If one wheel does not have enough traction, rotational torque will follow the path of least level of resistance and the wheel with small traction will spin while the wheel with traction will not rotate at all. Since the wheel with traction isn’t rotating, the automobile 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 normal cornering), an LSD will limit the quickness difference. This is an advantage over a regular open differential design. If one drive wheel looses traction, the LSD actions allows the wheel with traction to obtain rotational torque and invite 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 are based on a open up differential design. They possess another clutch pack on each of the axle side gears or axle shafts inside the final drive housing. 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 material is used to split up the clutch discs. Springs put strain on the axle aspect gears which put pressure on the clutch. If an axle shaft wants to spin quicker or slower than the differential case, it must conquer the clutch to do so. If one axle shaft attempts to rotate quicker than the differential case then your other will try to rotate slower. Both clutches will resist this action. As the speed difference increases, it turns into harder to overcome 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 goes to that wheel, the clutches resistance becomes a lot more apparent and the wheel with traction will rotate at (close to) the acceleration of the differential case. This kind of differential will most likely require a special type of liquid or some kind of additive. If the liquid is not changed at the proper intervals, the clutches can become less effective. Resulting in little to no LSD actions. Fluid change intervals vary between Final wheel drive applications. There is usually nothing incorrect with this design, but keep in mind that they are only as strong as a plain open differential.
Solid/spool differentials are mostly used in drag racing. Solid differentials, like the name implies, are totally solid and will not enable any difference in drive wheel acceleration. The drive wheels usually rotate at the same speed, even in a change. This is not an issue on a drag race vehicle as drag vehicles are traveling in a straight line 99% of the time. This can also be an advantage for vehicles that are getting set-up for drifting. A welded differential is a normal open differential that has acquired the spider gears welded to create a solid differential. Solid differentials certainly are a fine modification for vehicles created for track use. As for street use, a LSD option would be advisable over a solid differential. Every change a vehicle takes may cause the axles to wind-up and tire slippage. That is most visible when generating through a gradual turn (parking). The effect is accelerated tire wear and also premature axle failing. One big benefit of the solid differential over the other styles is its strength. Since torque is applied right to each axle, there is absolutely no spider gears, which will be the weak spot of open differentials.