Note: If you are likely to change your rear diff fluid yourself, (or you plan on opening the diff up for program) before you allow fluid out, make sure the fill port can be opened. Absolutely nothing worse than letting fluid out and having no way of getting new fluid back.
FWD final drives are very simple compared to RWD set-ups. Virtually all FWD engines are transverse installed, which means that rotational torque is created parallel to the path that the wheels must rotate. You don’t have to modify/pivot the path of rotation in the ultimate drive. The final drive pinion gear will sit on the finish of the result shaft. (multiple result shafts and pinion gears are possible) The pinion equipment(s) will mesh with the final drive ring equipment. In almost all cases the pinion and ring gear could have helical cut the teeth just like the remaining tranny/transaxle. The pinion gear will be smaller and have a much lower tooth count than the ring gear. This produces the ultimate drive ratio. The ring equipment will drive the differential. (Differential operation will be described in the differential section of this article) Rotational torque is delivered to the front wheels Final wheel drive through CV shafts. (CV shafts are generally referred to as axles)
An open up differential is the most common type of differential found in passenger cars and trucks today. It is definitely 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 necessary. “Spider gears” is certainly 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 aspect gears. The differential case (not housing) receives rotational torque through the ring equipment and uses it to drive the differential pin. The differential pinion gears ride on this pin and so are driven by it. Rotational torpue is certainly then transferred to the axle aspect gears and out through the CV shafts/axle shafts to the tires. If the automobile is travelling in a straight line, there is no differential actions and the differential pinion gears only will drive the axle side gears. If the vehicle enters a turn, the external wheel must rotate faster than the inside wheel. The differential pinion gears will begin to rotate as they drive the axle side gears, allowing the external wheel to speed up and the within wheel to decelerate. This design is effective provided that both of the driven wheels have traction. If one wheel does not have enough traction, rotational torque will observe the path of least resistance and the wheel with small traction will spin as the wheel with traction won’t rotate at all. Since the wheel with traction isn’t rotating, the vehicle cannot move.
Limited-slip differentials limit the quantity of differential action allowed. If one wheel starts spinning excessively faster compared to the other (more so than durring regular cornering), an LSD will limit the swiftness difference. That is an advantage over a normal open differential design. If one drive wheel looses traction, the LSD action allows the wheel with traction to get rotational torque and allow the vehicle to go. There are several different designs currently used 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 casing. 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. Friction material is used to separate the clutch discs. Springs place pressure on the axle aspect gears which put pressure on the clutch. If an axle shaft really wants to spin faster or slower than the differential case, it must overcome the clutch to take action. If one axle shaft tries to rotate faster than the differential case then the other will attempt to rotate slower. Both clutches will withstand this step. As the quickness difference increases, it turns into harder to conquer the clutches. When the automobile is making a good turn at low velocity (parking), the clutches offer little level of 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 apparent and the wheel with traction will rotate at (near) the rate of the differential case. This type of differential will likely need a special type of fluid or some kind of additive. If the liquid is not changed at the proper intervals, the clutches may become less effective. Leading to little to no LSD action. Fluid change intervals differ between applications. There is nothing wrong with this style, but keep in mind that they are just as strong as a plain open differential.
Solid/spool differentials are mostly found in drag racing. Solid differentials, like the name implies, are totally solid and will not really enable any difference in drive wheel velocity. The drive wheels at all times rotate at the same velocity, even in a convert. This is not an issue on a drag race vehicle as drag vehicles are traveling in a directly line 99% of the time. This can also be an advantage for cars that are getting set-up for drifting. A welded differential is a normal open differential that has experienced the spider gears welded to make a solid differential. Solid differentials are a good modification for vehicles created for track use. As for street use, a LSD option will be advisable over a good differential. Every convert a vehicle takes will cause the axles to wind-up and tire slippage. That is most obvious when driving through a sluggish turn (parking). The effect is accelerated tire use as well as premature axle failing. One big advantage of the solid differential over the other styles is its strength. Since torque is used directly to each axle, there is no spider gears, which are the weak spot of open differentials.